Status of theNorthern Leopard Frog

(Rana pipiens) in Alberta

Greg Wagner

Alberta Wildlife Status Report No. 9

Published By:

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Publication No. T/372ISBN: 0-7732-5134-8

ISSN: 1206-4912

Series Editor: David R. C. PrescottIllustrations: Brian Huffman

For copies of this report, contact:

Information Centre - PublicationsAlberta Environmental Protection

Natural Resources ServiceMain Floor, Bramalea Building

9920 - 108 StreetEdmonton, Alberta, Canada T5K 2M4

Telephone: (403) 422-2079

OR

Communications DivisionAlberta Environmental Protection

#100, 3115 - 12 Street NECalgary, Alberta, Canada T2E 7J2

Telephone: (403) 297-3362

This publication may be cited as:

Wagner, G. 1997. Status of the Northern Leopard Frog (Rana pipiens) in Alberta. AlbertaEnvironmental Protection, Wildlife Management Division, Wildlife Status Report No. 9,

Edmonton, AB. 46 pp.

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PREFACE

Every five years, the Wildlife Management Division of Alberta Natural Resources Service reviewsthe status of wildlife species in Alberta. These overviews, which have been conducted in 1991 and1996, assign individual species to �color� lists which reflect the perceived level of risk to populationswhich occur in the province. Such designations are determined from extensive consultations withprofessional and amateur biologists, and from a variety of readily-available sources of populationdata. A primary objective of these reviews is to identify species which may be considered for moredetailed status determinations.

The Alberta Wildlife Status Report Series is an extension of the 1996 Status of Alberta Wildlifereview process, and provides comprehensive current summaries of the biological status of selectedwildlife species in Alberta. Priority is given to species that are potentially at risk in the province (Redor Blue listed), that are of uncertain status (Status Undetermined), or which are considered to be atrisk at a national level by the Committee on the Status of Endangered Wildlife in Canada(COSEWIC).

Reports in this series are published and distributed by the Wildlife Management Division of AlbertaEnvironmental Protection, and are intended to provide detailed and up-to-date information which willbe useful to resource professionals for managing populations of species and their habitats in theprovince. The reports are also designed to provide current information which will assist the proposedAlberta Endangered Species Conservation Committee to identify species that may be formallydesignated as endangered or threatened under the Alberta Wildlife Act. To achieve these goals, thereports have been authored and/or reviewed by individuals with unique local expertise in the biologyand management of each species.

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EXECUTIVE SUMMARY

The Northern Leopard Frog has been designated as a �Red List� species in Alberta since 1991. InJanuary 1997 it was afforded with legal designation and protection as an �endangered� species underthe provincial Wildlife Act.

The species was formerly widely distributed and locally abundant in the prairies, foothills and centralparkland in the southern half of the province, but abrupt and dramatic population declines were notedin the late 1970s and early 1980s. Populations have remained at a low level since that time. Thespecies now appears to be extirpated over most of central Alberta, and with the exception of onerepatriated population, is apparently now absent from the entire North Saskatchewan River drainage. In southern Alberta, populations are absent or greatly reduced. Since 1981, the Northern LeopardFrog has been reported from 84 locations in the province, although evidence of breeding has onlybeen reported from 27 sites, and only seven sites in southeastern Alberta are considered to supportmajor breeding populations. The vast majority of these records have occurred since 1990. Monitoring data suggests that at least three of the major breeding populations are stable andreproducing successfully on an annual basis.

The cause(s) of population declines in Alberta is unknown. Although little studied, the decline inAlberta does not appear to be part of a regular cycle. Instead, it appears to be related to a singular,widespread factor affecting the survivorship of the species. The abrupt declines observed in Albertaappear to follow a similar pattern of sudden and massive declines witnessed in the upper mid-westernstates and prairie provinces during the 1970s.

Small population recoveries have been noted recently in Saskatchewan and Manitoba, providingpromise that recoveries may also occur in Alberta. Re-establishment of populations in formerlyoccupied areas with suitable habitat may occur as a result of dispersal from the remaining populationsin southern Alberta. However, our understanding of dispersal in the Northern Leopard Frog is limitedand it is difficult to predict the extent to which recolonization will occur. In some instances frogs mayhave to be transplanted from existing populations in order to establish populations elsewhere. Thismay be particularly true for central Alberta, which is separated from the remaining populations insouthern Alberta by vast stretches of arid land.

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ACKNOWLEDGEMENTS

This report was prepared with the cooperation, input and assistance of a number of individuals andI would like to extend my appreciation to the following: Wayne Roberts (Museum of Zoology,University of Alberta, Edmonton) for fruitful discussion and for making available museum records;Andy Didiuk (Environment Canada, Saskatoon) for making available survey data from the SuffieldNational Wildlife Area; Carolyn and David Seburn (Seburn Ecological Services, Kemptville, ON) forproviding references; Francis Cook (Canadian Museum of Nature, Ottawa) for reviewing museumrecords from northern Alberta; Cleve Wershler (Sweetgrass Consultants Ltd., Calgary) for providingbackground information and historic Leopard Frog observations; Tony Russell (University ofCalgary), Mark Steinhilber (Provincial Museum of Alberta, Edmonton), and the Field Museum ofNatural History (Chicago, IL) for making available museum records; Larry Powell (University ofCalgary) for providing references and recent Leopard Frog observations; Stephen Corn (AldoLeopold Research Institute, Missoula, MT) for providing references; Richard Lauzon (AxysEnvironmental Consulting Ltd., Calgary) and Mike Houser (Express Pipelines, Calgary) for providedrecent Leopard Frog observations; Dave Elphinstone (Parks and Recreation, City of Calgary) forproviding historic observation records; I. A. (Penny) Ohanjanian (Independent consultant, Kimberley,BC) for providing recent distributional information from British Columbia; Archie Balaski (DucksUnlimited, Brooks) and Don Watson (Ducks Unlimited, Lethbridge) for providing information onmanagement of Leopard Frogs at the Circle E project; and Kevin Wingert (Alberta EnvironmentalProtection, Red Deer) for providing observational records from Bocquene Lake.

This report also benefited from review comments provided by Dave Prescott and Steve Brechtel(Alberta Environmental Protection, Edmonton), Cynthia Paszkowski (University of Alberta), LarryPowell and Andy Didiuk. I would like to thank Steve Brechtel and Dave Prescott for giving me theopportunity to work on this project, and Jane Horb for producing the maps.

Preparation of the report was funded by the Wildlife Management Enhancement Fund of AlbertaNatural Resources Service, and the Alberta Conservation Association.

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TABLE OF CONTENTS

PREFACE ................................................................................................................................. iii

EXECUTIVE SUMMARY........................................................................................................ iv

ACKNOWLEDGEMENTS......................................................................................................... v

INTRODUCTION ......................................................................................................................1

HABITAT ..................................................................................................................................1

CONSERVATION BIOLOGY ...................................................................................................2

DISTRIBUTION ........................................................................................................................41. Alberta ........................................................................................................................42. Other Areas .................................................................................................................9

POPULATION SIZE AND TRENDS.........................................................................................91. Alberta ........................................................................................................................92. Other Areas ............................................................................................................... 13

LIMITING FACTORS.............................................................................................................. 151. Climate ...................................................................................................................... 152. Disease ...................................................................................................................... 163. Habitat Loss and Fragmentation................................................................................. 164. Livestock Activity...................................................................................................... 175. Road Kills.................................................................................................................. 176. Water Management.................................................................................................... 177. Harvest...................................................................................................................... 188. Introduction of Game Fish and Exotic Species ........................................................... 189. Contaminants and Wetland Acidification .................................................................... 18

10. Summary................................................................................................................... 19

STATUS DESIGNATIONS ..................................................................................................... 201. Alberta ...................................................................................................................... 202. Other Areas ............................................................................................................... 21

RECENT MANAGEMENT IN ALBERTA.............................................................................. 211. Planning..................................................................................................................... 212. Population Monitorig................................................................................................. 213. Habitat Securement, Protection and Enhancement...................................................... 224. Research.................................................................................................................... 225. Repatriation of Northern Leopard Frog Populations................................................... 23

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6. Public Awareness and Education................................................................................ 23

SYNTHESIS ............................................................................................................................ 23

LITERATURE CITED ............................................................................................................. 25

APPENDIX 1. .......................................................................................................................... 35

APPENDIX 2 ........................................................................................................................... 36

APPENDIX 3 ........................................................................................................................... 41

APPENDIX 4 ........................................................................................................................... 44

1

INTRODUCTION

Over the last 35 years, Northern Leopard Frog(Rana pipiens) populations have declineddramatically over much of the species� rangein North America. Abrupt population declineswere first noted in Alberta in 1979. Sincethen, populations appear to have beenextirpated over much of central Alberta andare absent or greatly reduced in southernAlberta. Only a handful of viable breedingpopulations currently remain in south-easternAlberta. Because of its virtual disappearancefrom the province, the Northern Leopard Froghas been designated as an �endangeredspecies*� under the Alberta Wildlife Act.

Since 1990, considerable effort has beenexpended trying to locate Northern LeopardFrogs in Alberta. Known breeding populationshave also been routinely monitored and studieshave been carried out on two of the breedingpopulations to provide more information ondispersal and the general ecology of thespecies in the province. This information, aswell as information from other jurisdictions, isreviewed in this report to provide an update onthe status of the Northern Leopard Frog inAlberta.

HABITAT

The Northern Leopard Frog requires a mosaicof habitat types to meet the annualrequirements of all life history stages. Generally, separate sites are used for breedingand overwintering. However, in some casesbreeding and overwintering may occur in thesame pond. This is particularly true in spring-fed wetlands. In Alberta, Northern LeopardFrogs are typically associated with clear waterthat is relatively fresh to moderately saline

* See Appendix 1 for definitions of selected statusdesignations

(Wershler 1992a). Other parameters of waterquality, however, vary widely between sites(Seburn 1992a).

Breeding occurs in shallow and warm standingwater associated with permanent andsemi-permanent wetlands, springs, dugouts,borrow pits, lakes, beaverponds, and thebackwaters and oxbows of rivers (Cook 1966,1984, Cottonwood Consultants 1986, Hine etal. 1981, Merrell 1977, Roberts 1981,Wershler 1992a). Temporary ponds andshallow lakes that are unsuitable for fish, andthat contain water until late July or August areconsidered to be the most favourable spawningsites for Northern Leopard Frogs (Hine et al.1981, Merrell 1977, Roberts 1981). Mostbreeding ponds contain a mixture of openwater and emergent vegetation. Although atsome sites in Alberta, breeding ponds aretotally encompassed by emergent vegetation(Wershler 1992a). Leopard Frog tadpoles aregenerally poorly adapted to cope with currentsand thus can develop successfully only in slowreaches of streams or backwaters (Roberts1981). In Minnesota, Leopard Frog densitieswere lower in stream habitats relative to ponds(Merrell 1977).

Following breeding and transformation, adult,juvenile and young-of-the-year frogs move tosummer feeding areas. Most often, these areasare located along the margins of waterbodies(Hine et al. 1981, Merrell 1977, Wershler1991a). Smaller, immature frogs appear to bemore closely tied to water; adults willoccasionally venture some distance from waterin the summer (Dole 1965b, Merrell 1977, C.Seburn 1994, Wershler 1991a). Thisdifference may be related to the greatersurface-area-to-volume ratio of smaller frogs,

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which makes them more prone to desiccation(C. Seburn 1994).

Preferred summer feeding habitat generallyconsists of open and semi-open areas withshorter vegetation (Cottonwood Consultants1986, Dole 1965a,b, Merrell 1977, Wershler1992a). Areas lacking vegetation or withclosely-clipped vegetation, such as found onheavily-grazed pasture, are avoided by frogs. Areas with tall, dense marsh vegetation,grasses or extensive shrub cover are alsoavoided, particularly by smaller frogs. Merrell(1977) notes that �in tall grass the frogs areless able to capture insects which tend to beout of their reach�. Merrell (1977) also notedthat Northern Leopard Frogs were seldomfound in heavily-wooded areas away fromwater. Seburn (1994), however, found nodifference in the density of frogs occupyingwooded versus non-wooded habitats in theCypress Hills of southeastern Alberta.

Unlike most of Alberta�s other species ofamphibians, Northern Leopard Frogsoverwinter in water (Russell and Bauer 1993). Overwintering frogs require well-oxygenatedwater that does not freeze to the bottomduring the winter. Hibernacula are most oftenlocated in springs, streams, spillways belowdams, or in deeper lakes and ponds (Cunjak1986, Emery et al. 1972, Merrell 1977,Roberts 1981). Frogs have been foundhibernating under rocks, logs, leaf litter orvegetation, or in depressions in sand or mud. Shallow breeding ponds and lakes areunsuitable for overwintering because of thedepletion of oxygen in the water column,which can lead to winterkill (see Babin andPrepas 1985). In southern Alberta, springsappear to provide critical overwintering habitatduring periods of drought when deeperpermanent water sources become limited(Wershler 1991a).

CONSERVATION BIOLOGY

Northern Leopard Frogs emerge fromoverwintering sites shortly after the ice beginsto melt and narrow strips of open, warmerwater form along the shoreline. Increasingtemperature probably acts as a stimulus,causing hibernating frogs to become moreactive and to move from deeper overwinteringareas to shallow water areas along the shore(Merrell 1977). Pace (1974) noted thatmigration from overwintering sites beginswhen water temperatures reach 9 to 12oC. Merrell (1977) observed that frogs did notleave the hibernacula until the air temperatureexceeded 13oC, or rose above the temperatureof the water. Short overland migrations maybe made between overwintering sites andbreeding ponds. In some instances, breedingmay also occur in overwintering habitats.

The timing and duration of breeding alsoappears to be temperature dependent. InAlberta, breeding occurs from late April to lateJune and breeding behaviour may occur whileice is still on ponds (Wershler 1992a). Yaremko (1994) observed males calling inearly May in southern Alberta when the airtemperature was 17.3oC and the watertemperature was 14.8oC. Cooler airtemperatures can suppress breeding activity,resulting in two or more mating periods andseveral size classes of larvae (Hine et al. 1981,Merrell 1977).

Sexually-mature males arrive at the breedingpond first and call while floating on the surfaceof the water. Males typically congregate insmall groups in the warmest parts of thebreeding ponds. Sexually-mature females areattracted to the calling of the males and arrivewithin a few days to a few weeks after themales (Hine et al. 1981). Egg laying occurs

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shortly thereafter. Egg masses are typicallylaid in shallow water on vegetation, branches,and, rarely, on the pond bottom (Corn andVivo 1989, Hine et al. 1981, Merrell 1977,Seburn 1992a, 1993, Yaremko 1994).

Females are believed to produce only oneclutch per year (Corn and Livo 1989) and it isthought that all eggs are laid in one mass(Noble and Aronson 1942). Egg masses maycontain between 600 and 7,000 eggs (see Cornand Livo 1989). Female body size has beenpositively correlated with clutch size in mostanurans (Slathe and Duellman 1973 cited inCorn and Livo 1989) and Corn and Livo(1989) suggest that the frequency distributionof the number of eggs in clutches could beused as a method to determine age structure ofbreeding females in Northern Leopard Frogpopulations.

The time of hatching is variable and is alsodependent on water temperature (Russell andBauer 1993). Hine et al. (1981) observedhatching five to nine days after egg laying. Cool weather, however can extend hatching to14 days or more after egg laying (Hine et al.1981). Merrell (1977) found that hatchingsuccess was greater in egg masses locatedbelow the surface of the water relative to eggmasses laid on the surface. In Wisconsin,about five percent of the eggs in each eggmass were lost to parasites, disease or otherfactors (Hine et al. 1981). Within a pond,Corn and Livo (1989) reported hatchingsuccess of between 70 and 99 %, althoughhatching success of individual egg masses wasas low as 30 %. They also note that factorssuch as flooding, droughts or periods of coldtemperatures can produce high mortality ofeggs, including failure of entire clutches.

Tadpoles remain close to egg masses afterhatching but disperse after a few days (Eddy

1976). Time to metamorphosis is temperature,and, perhaps, density dependent (Seburn1993), ranging from 60 to 90 days and mayoccur over several weeks at a single site. Survivorship, from total egg tometamorphosed young, averaged three percentin Minnesota (Merrell 1977) and from one tosix percent in Wisconsin (Hine et al. 1981). Mortality, however, can be complete ifbreeding ponds dry up before tadpoles becomefully transformed (Hine et al. 1981, Merrell1977). Seburn (1993) also observed that coolweather delayed the development of tadpoleswell into September in the Cypress Hills ofAlberta. She felt that these frogs would notsurvive because of the lack of time for them togain nutrient reserves before the onset ofwinter. In Alberta, tranformation generallyoccurs in July and early August (Seburn1992a, 1993, Wershler 1991a, Yaremko1994).

Tadpoles feed on floating vegetation anddetritus. At metamorphosis, frogs becomecarnivorous, taking only moving prey. Theirdiet includes insects, arachnids and other smallinvertebrates as well as small birds, gartersnakes, frogs and fish (Hine et al. 1981, Mooreand Strickland 1954, Rittschof 1975, Russelland Bauer 1993). Adults will also cannibilizenewly-transformed young (Russell and Bauer1993, Wershler 1992a).

Individuals take two or more years to becomesexually mature. However, in Minnesota it wasshown that in less dense populations youngfrogs grew rapidly and sexual maturity wasreached in one year (Merrell 1977). In denserpopulations, growth during the first summerwas minimal and young frogs may have takenthree years to reach sexual maturity (Merrell1977).

Annual adult mortality has been estimated to

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be approximately 60 % (Merrell and Rodell1968). In Manitoba, frogs decreased inrelative abundance in the population towardthe end of their fourth summer (Eddy 1976). Mortality rates of immature frogs arerelatively high. The ratio of young-of-the-year(YOY) frogs to sexually mature frogs rangedfrom about 15:1 to 20:1 in Minnesota (Merrell1977). Similar values were reported inWisconsin (Hine et al. 1981). In Alberta, C.Seburn (1994) observed ratios ofapproximately 120:1 in a breeding populationin the Cypress Hills. In 1994, overwinteringmortality of YOY frogs in this samepopulation was estimated at 93 % (Yaremko1994). This estimate may, however be highbecause it was based on the assumption thatthere was little dispersal from natal areas (C.Paszkowski, pers. comm.).

Following breeding, adults may remain in thevicinity of breeding ponds or disperse tosummer feeding ranges (Eddy 1975, Hine et al.1981, Merrell 1977, Seburn 1993). Usuallythese feeding ranges are located near water. Adults appear to establish home ranges in thesummer (Dole 1965a,b, Hine et al. 1981). InMichigan, home ranges tended to be smaller inareas where habitat was localized and limitedrelative to areas where habitat was morereadily available (Dole 1965b). In late summeror early fall, adults begin to migrate fromsummer feeding areas to overwintering sites(Eddy 1975, Merrell 1977). Roberts (1981)reports that Northern Leopard Frogs are activein Alberta until October, and exceptionally intoNovember. Little is known about theoverwintering ecology of Northern LeopardFrogs.

Following transformation, young-of-the-yearfrogs disperse away from natal ponds. InMichigan, Dole (1971) found that YOY frogsdisperse up to 800 m per night, and recaptured

two as adults five kilometers from their natalpond. Dole noted that this distance could haveonly been travelled overland. In the CypressHills, YOY frogs dispersed up to 2.1 km fromnatal ponds along aquatic corridors (Seburn etal., in press). However, the greatest distancetravelled over land was 0.4 km. One of thefrogs marked as a YOY in the Cypress Hills in1993 was recaptured in 1994 at a distance of8 km from the natal pond.

DISTRIBUTION

1. Alberta. - Northern Leopard Frogpopulations experienced drastic declines inAlberta near the end of the 1970s (see�Population Size and Trends�). Such declinesin population were accompanied by changes indistribution in the province. Accordingly,descriptions of the distribution of NorthernLeopard Frogs in Alberta are divided into�historic� and �current�, based on whetherobservations were collected before and during,or after, 1980.

Many authors (Cook 1984, Schueler 1982,Stebbins 1951, Wright and Wright 1949) haveshown the historic distribution of the NorthernLeopard Frog to be continuous in Alberta,with the range including most of southernAlberta and a band running along the easternborder of the province north to the NorthwestTerritories. However, a review of museumcollections (Appendix 2), and naturalists�records and published sources of information(Appendix 3) suggests that the species� rangewas largely restricted to two discontinuousparts of the province (Figure 1). These twoareas include the Slave River valley and KazanUplands in extreme northeastern Alberta andthe prairies, parkland and foothills of southernAlberta.

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Figure 1. Known observation and collection sites for Northern Leopard Frogs in Alberta prior to1981. See Appendices 2 and 3 for descriptions of sites.

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The occurrence of the species in northeasternAlberta is based on published accounts fromthe Slave River at Fitzgerald Settlement(Smith Landing) and Fort Smith near the turnof century (Preble 1908). Other records alsoexist from nearby sites in Saskatchewan andthe Northwest Territories (Harper 1931a,Hodge 1976, Logier and Toner 1961, Museumof Zoology, University of Alberta, unpubl.data). There is also a museum specimen fromthe Rocher River at the western end of LakeAthabasca (Appendix 2 - specimen NMC593),but it is likely that catalogue information forthe specimen is in error. This specimen wascollected by F. Harper, but he does notmention the specimen in subsequent reportsabout his trips in the area (Harper 1931a,b). The collection date for the specimen, 5 August1914, also corresponds to the date thatNorthern Leopard Frogs were collected at theNatla Rapids on the Talston River, NorthwestTerritories (Harper 1931a). Considering thesefactors, it is likely that the specimen wasactually collected at the Talston River and notat the Rocher River (F. Cook pers. comm.).

In the southern half of the province, thespecies� range extended across the prairies,foothills and parkland from the U.S. bordernorth to Edmonton. Within this region, theNorthern Leopard Frog was continuouslydistributed along major rivers and tributarieswith scattered populations associated withlakes, springs and irrigation reservoirs. Although the species appears to have beenwidely distributed in the western half of thecentral parkland, there are only a handful ofrecords from the eastern portion of theparkland north of the Battle River (Figure 1).

In southern Alberta, the western extent of therange was the foothills and the easternperiphery of the Rockies at lower elevations. There are records from the northeastern and

eastern edges of Waterton Lakes NationalPark and from the Bow Valley corridor nearBow Valley Provincial Park and the YamnuskaCentre (Appendix 2 and 3, Salt 1977). Historic records from the mountains arelacking (Bow Valley Naturalists 1978,Holroyd and Van Tighem 1983, McIvor 1994,McIvor and McIvor 1995, 1996 - BanffNational Park and Bow Valley Corridor;Holroyd and Van Tighem 1983 - JasperNational Park; C. Wershler pers. comm. -Waterton Lakes National Park; Salt 1977 -Kananaskis Country) and Salt (1979)considered the species to be of �hypothetical�occurrence in Alberta�s Rockies. It should benoted, however, that many of the amphibiansurveys from the Rocky Mountains wereconducted after abrupt population declineswere observed elsewhere in the province. Salt(1979) also mentions a museum specimencollected near Jasper, but that record could notbe located during research conducted for thispaper.

Outside of the extreme northeastern corner ofAlberta, there are few historical records fromnorth of Edmonton and Russell and Bauer(1993) indicate that �the true distributionnorth of 55oN is poorly known�. It should benoted, however, that the National Museum ofCanada and the University of Alberta (in 1976,W. Roberts, pers. comm.) have both madeextensive amphibian collections in northernAlberta, but have not encountered NorthernLeopard Frogs. In some areas, extensivebiophysical surveys have also failed to locatethe species (e.g. Roberts and Lewin 1979). Although information on the historicdistribution of herpetofauna in northernAlberta is largely lacking, the data that doesexist suggests that the Northern Leopard wasonly locally and sparsely distributed in theboreal forest. North of Edmonton, museumspecimens have been collected at Valleyview,

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Whitecourt and at sites along the Smoky Riverthat were initially identified as NorthernLeopard Frogs (Appendix 2). Thesespecimens are of tadpoles, which can bedifficult to identify. A recent preliminaryexamination of the specimens indicates thatthey may have been misidentified (F. Cook,pers. comm.). Until further confirmation,these records must be considered dubious. There is also a specimen record (USNM 9343)from the late 1880s with the site locality of�Athabaska River, British America R.�(Yarrow 1882, pg. 179; Cope 1889, pg. 403). The exact location of this record is, however,difficult to pinpoint. Northern Leopard Frogshave also been observed along the LesserSlave River (Wershler 1991a), at Lesser SlaveLake Provincial Park (Griffiths 1976 cited inBradley 1980), and at Thunder Lake, LongLake and Cross Lake Provincial Parks(Spalding 1980, Wershler 1991a). It should benoted, however that Griffiths does not mentionNorthern Leopard Frogs in her account of thewildlife of Lesser Slave Lake Provincial Parkpresented in Spalding (1980). The Fort Smithsite location shown in CottonwoodConsultants Ltd. (1986), Alberta Fish andWildlife (1991) and Wershler (1991a) is basedon an unconfirmed sightings reported toRoberts and Lewin (1977).

Since 1980, there has been a southerncontraction of the provincial range of theNorthern Leopard Frog, and the species nowappears to be largely extirpated from thecentral parkland, and is apparently absent fromthe entire North Saskatchewan River drainage (Figure 2). With the exception of the KazanUplands in northeastern Alberta, where therewere observational records from BocqueneLake in 1991 (K. Wingert, pers. comm.) andfrom Wylie Lake in 1983 (Wallis and Wershler1983), there have been no observations ofNorthern Leopard Frogs north of the Red

Deer region since 1979.

In 1990 and 1991, extensive presence/absencesurveys were conducted at sites in southernAlberta where Northern Leopard Frogs wereknown to occur historically, or where therehad been recent unconfirmed sightings of thespecies (Hofman 1991, Seburn 1992a,Wershler 1991a, 1992a). These surveysrevealed that Leopard Frog populations werelocally abundant at three sites in the CypressHills, along the Milk and South Saskatchewanrivers, along the lower reaches of the Bow andRed Deer rivers, and at sites along the LittleBow River, and Canal and Manyberries creeks(Figure 2). Leopard Frogs were also found tobe present at a few sites in the central parklandnear Red Deer (Figure 2). Population surveysconducted at the proposed Suffield NationalWildlife Area from 1994 to 1996 locatedadditional populations along the SouthSaskatchewan River (A. Didiuk, pers. comm.). Since 1990, additional populations have alsobeen discovered along Willow Creek (D. A.Westworth and Associates 1993), along theRed Deer (R. Lauzon, pers. comm.), Milk (L.Powell, pers. comm., Wershler and Smith1996) and Sheep (Alberta AmphibianMonitoring Program, unpubl. data) rivers, andalong an irrigation drainage near Bow City(pers. obs.).

In total, Northern Leopard Frogs have beenobserved at 84 locations since 1981 (with thevast majority occurring since 1990; Figure 2,Appendix 4), but direct (tadpoles ordeveloping or recently transformed young) orindirect (calling males) evidence of breedinghas been reported from only 27 sites in theprovince (Figure 2, Appendix 4). Only sevenof these sites appear to be of major breedingpopulations (>100 young-of-the-year

8

Figure 2. Known site records for Northern Leopard Frogs in Alberta since 1981. Detaileddescriptions of observations are given in Appendix 4.

observed; Figure 2, Appendix 4). Thesepopulations are located at Bow City, EmpressCreek, Jenner Pond, Kennedy�s Coulee, LittleBow River, Prince�s Spring (near Bindloss),and Sexton Creek (Cypress Hills).

2. Continental Range. - The NorthernLeopard Frog is widely distributed over muchof central North America (Figure 3), and withthe exception of range contractions resultingfrom local extirpations of breeding populations(particularly in western North America), thecurrent and historical ranges are generallysimilar. The species is broadly distributedacross the southern half of Canada east of theRockies. The range extends as far north assouth-central Northwest Territories, and adisjunct population occurs in southernLabrador (Cook 1984). In eastern BritishColumbia, the Northern Leopard Frog occursin the Kootenay and Columbia river valleysand in the vicinity of Creston at the southernend of Kootenay Lake (Orchard 1992). Thespecies has also been successfully introducedon Vancouver Island and Newfoundland(Cook 1984, Green 1978).

In the United States, the species� rangeextends from the Canadian border south alongeastern Washington and Oregon to California,Arizona and extreme southern New Mexicoand then north into the northern plains states,and east through the Ohio Valley to NewEngland (Baxter and Stone 1980, Russell andBauer 1993, Stebbins 1951).

POPULATION SIZE AND TRENDS

1. Alberta. - Until recently, the herpetofaunaof Alberta has received little attention fromeither scientists or naturalists (Russell andBauer 1993, Wershler 1991a). The NorthernLeopard Frog is no exception. Populationsurveys were not conducted before the 1980s,and there is little formal documentation ofhistoric population levels in the province. Much of our understanding of the historicdistribution and abundance of the species isbased on biophysical inventories in specificareas of the province, museum collections, andthe records and recollections of naturalists. These sources indicate, however, thatNorthern Leopard Frogs were historicallycommon and widely distributed south ofEdmonton, south and west of the Battle River(Cottonwood Consultants 1986, Roberts1981, 1987, 1992, Russell and Bauer 1993,Wershler 1991a). Documented reportsindicate that the species was common insoutheastern Alberta (Lewin 1963), along theMilk River valley (Wallis 1976), in the CypressHills (Halladay 1965), at several natural areasin Calgary (Bird 1973, 1974, Pinel 1980),south and west of Red Deer along the Ravenand Red Deer rivers and Kneehill Creek(Roberts 1981), and along Kilini Creek west ofEdmonton (W. Roberts pers. comm., Spalding1980). Specimen records of the NationalMuseum of Canada and Museum of Zoology,University of Alberta, also reveal that LeopardFrogs could readily be collected at a number oflocations in small geographical areas in theprairies and foothills of southern Albertaduring the 1950s and 1960s. Extensive field

9

surveys conducted in southern Alberta in the1970s indicate, however, that relative to theStriped Chorus Frog (Pseudacris triseriata),Leopard Frogs were only locally abundant(Wershler 1991a). This is no doubt related tothe species� need for well-oxygenatedoverwintering sites (Lewin 1963). In

summary, although quantitative survey dataare lacking, the information that does existindicates that Northern Leopard Frogs werehistorically widely distributed but locallyabundant south of Edmonton, and south andwest of the Battle River.

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Figure 3. North American range of the Northern Leopard Frog (adapted from Stebbins 1985).In Alberta, abrupt population declines were first noted south and west of Red Deer in 1979

11

(Roberts 1981). Between 1976 and 1978,Northern Leopard Frogs were abundant atsites along Kneehill Creek, along the Ravenand Clearwater rivers, and along the upper andmiddle reaches of the Red Deer River, andpopulations were reproducing successfully(Roberts 1981). However, extensive searchingin the area in 1979 and 1980 failed to locateany Leopard Frogs (Roberts 1981), andongoing annual surveys have not yieldedsubsequent records in these areas (Roberts1987, 1992, 1995, pers. comm.). A similarpattern has been noted in Calgary, whereannual monitoring of natural areas within thecity by the Calgary Field Naturalists Societyhas not produced records of Northern LeopardFrogs since the late 1970s (M. Babey, pers.comm.). In 1979, extensive searches werealso conducted at other sites where LeopardFrogs had been known to occur but only oneindividual was found overwintering in the MilkRiver (Wershler 1991a). At the same time,naturalists, scientists, fishermen and farmers insouthern Alberta were queried as to whetherthey had seen any Leopard Frogs. Theseenquiries yielded no recent records, althoughmany of the people recalled that the specieswas previously abundant in many areas(Roberts 1987).

It is unknown when population declines firstoccurred in other parts of southern Alberta,but declines appear to have been complete inmany areas by at least the early- to mid-1980s(Cottonwood Consultants 1986, Roberts1981, 1987, Wershler 1991a). Between 1979and 1989 there were few reports of NorthernLeopard Frogs from anywhere in the province. In the early 1980s, naturalists were asked toincrease their surveillance of reptile andamphibian populations in Alberta (Roberts1981, 1982), but few reports of Leopard Frogsresulted. Many of the reports that did come in

turned out to be other species (Wershler1991a). Field surveys conducted in southernAlberta in the early and mid-1980s revealedthat Leopard Frogs were absent from manyhistorically-occupied sites and, where they didexist, populations were greatly reduced fromhistoric levels (Cottonwood Consultants 1986,Roberts 1987, Wershler 1991a). Thesesurveys located a few individuals along the St.Mary�s River and Pinepound Creek, andlocally-abundant populations at Prince�sSpring (near Bindloss), along the Milk Riverand along the lower Bow River (CottonwoodConsultants 1986, Roberts 1987, Wershler1991a).

Populations at Prince�s Spring, Sexton Creekand Empress Creek have been monitored since1990 (Table 1). Censusing amphibianpopulations can be problematic andpopulations can fluctuate widely between years(Pechmann et al. 1991), so caution must beexercised when comparing population trendsbetween sites and between years. Nonetheless, the available data indicates thatthe breeding populations at these three sitesare stable and reproducing successfully on anannual basis.

It should be cautioned that data limitationsmake it somewhat difficult to identifylong-term population trends in the province. At some locations there are long-term,qualitative data that indicate dramaticpopulation declines have occurred over the last20 years. However, elsewhere in southernAlberta population trends have largely beendetermined from presence/absence surveysconducted in 1990 and 1991 at locationswhere historic occurrence was recorded frommuseum specimens, naturalists� records orpublished accounts in the literature (Hofman1991, Seburn 1992a, Wershler 1991a, 1992a).

Table 1. Northern Leopard Frog census results from Prince�s Spring, Empress, and Sexton Creek

12

populations. Numbers for Prince�s Spring are maximum individuals observed; valuesfor other populations are maximum linear density per 100 m (unless otherwise noted).

Prince�s Spring EmpressSexton Creek

(Upper Marsh)Sexton Creek

(Lower Marsh)

Year Adults YOY Adults YOY Adults YOY Adults YOY

1990 5 >272 - - 2 62 16 594

1991 0 >388 9 397(a) 6 9 21 629

1992 3 213-245 8 62 28 162 28 276

1993 12 >300 12 191 7 676(a) 11 28

1994 >12 >119 8 109 9 441 12 496

1995 17 >74 - - - - -

Sources: Prince�s Spring - Hofman 1992, 1994a, b, 1995, Wershler 1991b, 1992b; Empress - Seburn 1992a, 1993, 1994, Yaremko1994; Sexton Creek - Seburn 1992a, 1993, 1994, Wershler 1991a, Yaremko 1994.(a) Minimum estimate based on mark-recapture census

Because of time constraints and the largegeographic area surveyed, many of thelocations surveyed were visited on only oneoccasion and many of the sites were visitedoutside of the breeding season. Repeat visitswere generally only made to sites whereevidence of breeding was found on the initialsite visit or from other earlier surveys of thesite. Corn (1994) notes that there can be someproblems with using such surveys to determinelong-term population trends. First, single sitevisits may fail to detect individuals that areactually present, which would result in anoverestimation of population declines (Corn1994). For example, during the breedingseason Northern Leopard Frogs may not callon certain day or at certain times of the day(Cook 1994) and breeding populations may goundetected during brief, single call surveys ata site. After the breeding season, adults mayalso be difficult to find because of dispersal

away from breeding ponds (Corn 1994). Second, the use of museum, naturalists� andpublished records may not provide an accuratebaseline of historic population levels, and mayignore population trends resulting from thenatural processes of local extinction andrecolonization (Corn 1994). This isparticularly true if records are combined overseveral decades. Furthermore, museum recordsand anecdotal accounts do not alwaysrepresent breeding populations, or they mayrepresent records from marginal habitatswhere breeding may occur but is rarelysuccessful (Corn 1994).

Giving due consideration to data limitations, itis still apparent that Northern Leopard Frogpopulations have declined dramatically insouthern and central Alberta over the lasttwenty years. Within the central parkland,declines occurred abruptly in 1979 (Roberts

13

1981).

2. Other Areas. - Northern Leopard Frogshave long been used as laboratory and researchanimals in North America and wild frogs havetraditionally supplied this market. Beginning inthe early 1960s, harvesters for biologicalsupply houses noted sudden and dramaticdeclines in leopard frog numbers in manylocalities in the midwestern U. S. andCalifornia (Gibbs et al. 1971, Hine et al.1975). Biological supply houses also observeda general decline in the health of the animals(Gibbs et al. 1971, Hine et al. 1975). Frogsoften died in holding tanks before they couldbe shipped to customers, and it was notuncommon for 50 to 90 % of the frogs to diefrom a septicemia resulting fromoverwhelming infection with the bacteriaAeromona hydrophila. This was not surprisingas most frogs were placed under a great dealof stress between the time of capture anddelivery to end users, and were probably verysusceptible to disease (Gibbs et al. 1971). Approximately five to 10 % of the frogscaught in the northeastern and north-centralUnited States also had kidney tumours (Gibbset al 1971). Based on the difficulty ofobtaining frogs for laboratory use and reportsof frog declines from harvesters, Gibbs et al.(1971) estimated that Northern Leopard Frogpopulations declined by 50 % in the U. S.during the 1960s. They blamed the decline onoverzealous harvesting and habitat loss.

The abrupt and widespread populationdeclines previously described for Albertaappear to have been parallelled over much ofthe species� range in the upper midwesternstates and prairie provinces during the 1970s. The initial declines were noted in centres ofhigh frog densities in the upper midwest states,most notably in Michigan, Minnesota,Wisconsin and South Dakota in the late 1960s

and early 1970s (Hine et al. 1975, 1981,Rittschof 1975) The die-off spread rapidlyand, within a year or two, declines of NorthernLeopard Frogs and other related species ofLeopard Frog were noted as far south asMexico (Koonz 1992).

Abrupt population declines occurred shortlyafterward in Manitoba (Hine et al. 1981,Koonz 1992, Wershler 1991a). Traditionally,the Northern Leopard Frog harvest inManitoba has made up a large portion of theNorth American market, with as much as50,000 kg of frogs being shipped annually tobiological supply houses in the U.S. (Koonz1992). By 1976, however, no exports weremade, as Northern Leopard Frogs had virtuallydisappeared from the province, particularlyfrom areas such as Lake Manitoba, thatformerly supported the greatest densities offrogs (Koonz 1992). Windrows of dead frogswere observed on shorelines along LakeManitoba and piles nearly a metre high werenoted in artesian wells (�frog holes�) used ashibernacula. Small, isolated populations (e.g.,on golf courses, stock ponds and islands)survived through to 1983, when somerecovery was noted and exports resumed atmuch reduced levels (Koonz 1992). Sincethen, Northern Leopard Frog populations haveincreased in some areas while remainingextremely low in others (Koonz 1992). Thespecies has not reoccupied frog holes, andappears to be only slowly occupying whatwere once major centres of population. Although Northern Leopard Frogs havemoved back into much of their traditionalrange, they have not approached historicpopulation densities. Habitats once supportingthe highest frog densities continue to showconsiderable population fluctuations (Koonz1992).

From Manitoba, the die-offs apparently spread

14

westward. As in Alberta, there is little data onthe historic distribution and abundance ofNorthern Leopard Frogs in Saskatchewan. However, available data suggest thatpopulation levels reached a low in the early tomid-1970s (Seburn 1992b). Over the last fiveyears there has been an increased number ofreports in the province, which suggests thatthe species may be increasing locally (A.Didiuk, pers. comm.). In many areas,however, population densities are still lowrelative to historic levels (W. Harris, pers.comm.). It should also be noted that increasedreporting in recent years may also be related toincreased interest in the species brought aboutby the establishment of the SaskatchewanAmphibian Monitoring Project andSaskatchewan Herpetology Atlas Project. Major populations increases have been notedrecently in some areas of the province. In thelate 1980s, for example, Northern LeopardFrogs were difficult to find in GrasslandsNational Park (W. Harris, pers. comm.). However, in 1991 the species was found to becommon in many areas of the park (W.Roberts, pers. comm.) and in 1995 and 1996,it was observed to be common along both theFrenchman River valley and along Rock Creek(L. Powell, pers. comm.). Various age classes,including a large number of adults wererecorded during the 1995 and 1996 surveys.

Recent population surveys have beenconducted over much of the historic range ofthe Northern Leopard Frog in the Kootenayand Columbia river valleys of southeasternBritish Columbia (Ohanjanian and Teske 1996,I. Ohanjanian, pers. comm., Orchard 1992). Frogs, however, have only been found nearCreston (I. Ohanjanian, pers. comm., Orchard1992). The exact timing of the declines inBritish Columbia is unknown, but they appearto have occurred over the last 10 to 15 years(Orchard 1992). The cause of the decline is

unknown, but in some areas it may be relatedto habitat loss (Orchard 1992).

Population declines have been reported from avariety of other jurisdictions in the westernU.S. As was the case in Alberta, mostpopulations have been poorly studied andthere is lack of historical data. Most declineshave also been noted after the fact, soattributed causes for the declines have beenbased more on correlative rather thanexperimental evidence (Corn 1994). To date,researchers have not linked the declinesobserved in the western U.S. with the abruptand widespread population die-offs observedin the upper midwestern states and prairieprovinces during the 1970s.

The Northern Leopard Frog was formerlywidely distributed across Montana, but is nowapparently absent over much of the westernhalf of the state (Reichel and Flath 1995). Thespecies is still common in the southeasterncorner of the state, but its status is uncertain incentral and northeastern Montana (Reichel andFlath 1995). Population declines appear tohave occurred over the last 10 to 15 years. Elsewhere in the western U. S., declines havebeen noted in eastern Washington (Andelmanand McAllister 1994, Koch et al. 1996,Leonard and McAllister 1996), eastern Oregonand southern Idaho (Koch et al. 1996),Colorado and Wyoming (Baxter and Stone1980, Corn and Fogleman 1984, Corn et al.1989, Hammerson 1982, Weise 1990), Nevada(Panik and Barrett 1994), and Arizona andCalifornia (Clarkson and Rorabough 1989,Fernandez and Bagnara 1995, Hayes andJennings 1986, Schwalbe and Rosen 1988,Sredl and Waters 1995).Recent major populations declines have notbeen noted in eastern Canada (Bishop andPetit 1992), but Gilbert et al. (1994) note thatlocal population declines have occurred in

15

Quebec because of habitat loss.

LIMITING FACTORS

Over the last 30 to 50 years, amphibianpopulations have declined dramatically andaround the globe, a relatively large number ofspecies are in jeopardy (Barinaga 1990,Blaustein and Wake 1990, Wyman 1990). This is true of many species found in Canada(Bishop and Petit 1992, Cook 1970, Quinn1991), including the Northern Leopard Frog. In this, and other, species, declines can oftenbe explained in relation to natural populationfluctuations (Pechmann et al. 1991), extremesin climatic conditions (Barinaga 1990) oranthropogenic factors such as habitat loss,acidification, contaminant releases and theintroduction of non-native species (Baringa1990). However, in many other cases thedeclines cannot be explained and haveoccurred in relatively pristine environments orin areas where there has been no recentobvious disturbance. Such declines are oftencharacterized by abrupt, massive andwidespread population declines of one or morespecies. At the same time, populations ofother amphibian species occupying the samearea and similar habitats show no signs ofdecline.

In the past few years, comprehensive researchand monitoring programs have been initiatedworld-wide to determine the extent andcause(s) of amphibian declines. Among thefactors being examined are disease, thereduction in the ozone layer and accompanyingincrease in ultraviolet radiation, changingweather patterns and climatic extremes, acidrain and chemical contaminants, theintroduction of exotic species, and habitat lossor fragmentation. The following sectionsoutline factors which may be applicable todeclines in Northern Leopard Frog populations

in Alberta. Although the focus of this sectionis on human-induced factors, a number ofnaturally-occurring factors are also includedbecause of their possible synergistic impactswith other factors.

1. Climate. - Climatic conditions have a majorinfluence on Northern Leopard Frogpopulations (Merrell 1977). In general, duringwet years there will be increase in the amountof breeding and overwintering habitat allowingpopulations to expand and providingopportunities for dispersal and colonization ofunoccupied areas of suitable habitat. In drieryears, available habitat will diminish causing areduction in population levels. Some localpopulations will also become extinct becauseof a lack of habitat. For example, drought inthe 1930s caused a general decline inamphibian populations in southern Alberta(Fowler 1935). Drought has been suggestedas a possible reason for the decline anddisappearance of Northern Leopard Frogpopulations in Washington, Oregon, Idaho,Montana and Colorado (Corn and Fogelman1984, Koch et al. 1996).

During the late 1970s and 1980s, droughtconditions prevailed over much of southernAlberta. The accompanying loss of wetlandhabitat probably caused general populationdeclines and the extinction of some localpopulations in that area during this period(Wershler 1991a). Drought, however, hasbeen dismissed as the cause of the abrupt andwidespread population declines observed insouthern Alberta since 1979 (Roberts 1981,1987, 1992, Wershler 1991a). These authorsargue that while reduction in wetland habitatand reduced winter stream flows might explainthe disappearance of frogs in some areas, itwould not explain the simultaneousdisappearance of frogs in spring-rich areassuch as along Kilini Creek and the Clearwater

16

River or at deep-water overwintering sites atmajor lakes and reservoirs. These assertions,however are based on limited data and there isthe need for further research to determine theextent to which Northern Leopard Frogpopulations are affected by climatic conditionsin southern Alberta.

2. Disease. - Mass mortality of amphibiansfrom disease is not uncommon and may be anatural feature of the biology of a species, orit may be induced by environmental stressors(Corn 1994, Crawshaw 1992). Amphibiansare known to be susceptible to a variety ofdiseases including many diseases of fish(Crawshaw 1992). Mortality in NorthernLeopard Frogs has often been associated withthe condition of �red leg� (Gibbs et al. 1971,Hine et al. 1981, Koonz 1992), which is not adisease itself but rather a condition of kidneyfailure (Koonz 1992). It is often associatedwith infection by Aeromona hydrophila, anaturally-occurring and widespread bacterium. Ordinarily, this pathogen only affectsindividuals whose immune systems have beenweakened by stress, and not entirepopulations. Overwintering mortality inNorthern Leopard Frogs has also beenattributed to a herpesvirus (Lucke tumourvirus) that causes renal carcinomas (Hunter etal. 1989, McKinnel 1973, 1980).

Roberts (1995) suggests that the pattern ofdecline observed in the upper midwesternstates and the prairie provinces �was like thatexpected if a plague started in the east andspread across the continent�. However, thereis little conclusive evidence that disease wasresponsible for the abrupt and dramaticpopulation declines observed in Alberta andelsewhere (Hine et al. 1981). The lack ofcalling males in the Red Deer area during thespring of 1979 suggests that mortalityoccurred in the fall or winter (Roberts 1981).

This is similar to the pattern of mortalityobserved in Wisconsin (Hine et al. 1981). Incidences of overwintering mortality werenoted in the Clearwater River in 1976 (Roberts1992). Similar to other locations, mortality inthe Clearwater River was associated with thecondition of �red leg�. In this case, however,only individuals were affected and healthypopulations persisted in the area for the nexttwo years.

3. Habitat Loss and Fragmentation. - Habitatloss and fragmentation can impact LeopardFrog populations at two levels. Locally,populations are dependent on a variety ofhabitat types to meet the annual requirementsof various life history stages (Merrell 1977).The loss of any one of these habitats or theimpairment of movement between habitattypes could result in the demise of the entirepopulation. Relative to many otheramphibians, this requirement for a seasonalmosaic of habitat types makes NorthernLeopard Frogs particularly vulnerable tohabitat loss or alteration. On a regional basis,many amphibian populations exist asmetapopulations, represented by a set of linkedbut geographically discrete local populationsoccupying suitable habitats (see Blaustein et al.1994). Local populations will fluctuatebecause of environmental factors and naturalstochastic mechanisms and local extinctionsmay occur. But regionally, populations will bemaintained through dispersal of individualsbetween populations and recolonization ofvacant habitat. However, habitat loss canresult in populations becoming isolated orseparated by greater distances. This can limitimmigration from neighbouring populations,which can lead to a decrease in the fitness ofindividuals in the isolated population becauseof reduced gene flow and increase thelikelihood that the isolated population willbecome extinct because of random population

17

fluctuations (Blaustein et al. 1994, Corn1994).

Habitat loss is believed to be one of the causesof Northern Leopard Frog declines inWashington, Oregon, Idaho and Montana(Koch et al. 1996) and in Dickson County,Iowa, habitat loss has caused populations todecline by two to three orders of magnitudeover the last 70 years (Lannoo et al. 1994). Over the last half of this century, wetlanddrainage has been extensive in southernAlberta. For example, it is estimated that 60 %of the wetlands have been lost in the aspenparkland (Alberta Water ResourcesCommission 1990), and over 90 % of wetlandmargins in the prairie and parkland have beenimpacted by agricultural activities (Turner etal. 1987). The extent to which wetland lossand alteration have impacted NorthernLeopard Frog population in the province isunknown, but in some areas populationdeclines have no doubt been substantial.

4. Livestock Activity. - In California, Jennings(1988) considered alterations to riparianvegetation by livestock grazing to be animportant factor in the decline of ranid frogspecies. Livestock have been present at anumber of sites in southern Alberta whereLeopard Frogs have been found (Seburn1992), and livestock disturbance is considereda threat to frog populations at Prince�s Spring,Empress Creek and Sexton Creek (Seburn1992a, 1993, Wershler 1991b, 1992b,Yaremko 1994). Livestock activity hasresulted, or could result, in the followingdisturbances: 1) grazing and trampling havereduced vegetation cover and created drier soilconditions in riparian areas, reducing thequality of summer habitats; 2) cattle tramplingalong the shores and in the water have causedan increase in water turbidity, which couldhave negative effects on tadpole and egg

development; and 3) cattle movements alongthe shoreline and wetlands could potentiallydislodge or trample egg masses. Livestockdefecation in or around overwintering pondscould result in increased nutrient loading in thepond and increase the likelihood of winterkill.

5. Road Kills. - In Minnesota and Ontario,road kills account for the death of a largenumber of Northern Leopard Frogs,particularly in the spring and fall when frogsare moving between overwintering andbreeding sites (Ashley and Robinson 1996,Merrell 1977). Until recently, road kills werenot thought to be a major concern in Alberta. In 1994, Yaremko (1994) reported the deathof a small number of frogs along a frequently-travelled trail in a meadow adjacent to theupper marsh at Sexton Creek. This area wasused as summer habitat by the frogs and largenumbers of YOY that disperse through thearea.

6. Water Management. - Wershler (1991a)noted that a number of water-managementpractices could negatively impact NorthernLeopard Frogs in Alberta. The raising andstabilization of water levels to enhancerecreational activities or to improve habitat forother species, such as fish or waterfowl, canlower the habitat potential for frogs byreducing the amount of wetland vegetation. Drawdowns of wetlands for vegetationmanagement can impact tadpoles if thedrawdown occurs before transformation. Similarly, flooding of artificial wetlands in thespring could dislodge eggs. Wershler (1991a)also indicated that onstream dams alterphysical processes along rivers. This couldlimit the creation of side channels and oxbows,which are important habitats for frogs. Onstream dams can also reduce winterstreamflow levels, which could increaseoverwintering mortality.

18

Seburn (1993) raised concerns that thedestruction of beaver dams could reduceavailable Leopard Frog habitat in the CypressHills.

7. Harvest. - Throughout its range, theNorthern Leopard Frog has been collected forteaching and research needs, bait and evenfood (Gibbs et al. 1971, Koonz 1992,Wershler 1991a). In Alberta, commercialharvest has long been illegal, so the extent ofcollecting has probably been limited to thecapture of frogs for fish bait and to thecollecting and raising of tadpoles and frogs bychildren. In the past, these were probablyrelatively benign activities, but with the recentpopulation declines, any loss must beconsidered unacceptable. The collecting offrogs by children has been noted recently inMedicine Hat and at Writing-on-StoneProvincial Park (Wershler 1991a).

With the recent designation of the NorthernLeopard Frog as an �endangered species� (see�Status Designations�, below) it is now illegalto collect frogs for any purposes. With therecent designation, ongoing efforts will have tobe made to inform the public, particularlychildren, that collecting could be detrimentalto frog populations.

8. Introduction of Game Fish and ExoticSpecies. - In many parts of western NorthAmerica, declines of amphibian populationshave been linked to the introduction of gameand other species of fish (Corn 1994, Corn andPeterson 1996). Fish introductions are alsothought to pose a threat to Northern LeopardFrogs. The species is believed to select againstfish-bearing waterbodies for spawning as manyfish species are known to prey on tadpoles. Game fish are also known to prey onoverwintering frogs (Emery et al. 1972). In the

White Mountains of Arizona, populationdeclines have also been linked to theintroduction of crayfish (Orconectes virilis,Fernandez and Bagnara 1995).

The extent to which sport fish introductionshave impacted Leopard Frog populations inthe province is unknown, but the matter is acause for concern. Seburn (1992a) noted thatan individual had wanted to introduce sportfish into a beaver pond at Sexton Creek. Thiscould potentially have had dire consequencesfor the important Leopard Frog populationoccupying the site.

The introduction of Bullfrogs (Ranacatesbeiana) has also been implicated in thedecline of Northern Leopard Frog populations(Hammerson 1992, Koch et al. 1996, Lannooet al. 1994, Panik and Barrett 1994, Schwalbeand Rosen 1988, Weise 1990). Bullfrogs havenot been introduced into Alberta. However,Bullfrogs have recently been introduced intowestern Montana, which coincidentally iswhere the greatest Leopard Frog declines havebeen noted (Reichel and Flath 1995). WhetherBullfrogs have played a role in the decline isunknown. It is also unknown whether thespecies will expand its range into this province,but the potential impacts on amphibianpopulations, and on biodiversity in general, iscause for concern.

9. Contaminants and Wetland Acidification.- Because of their use of subcutaneousrespiration, use of water for egg laying,reliance on both terrestrial and aquaticenvironments, and the different positions oflarvae and adults in the food chain, amphibiansare particularly vulnerable to a variety ofcontaminants, including pesticides (Bishop1992, Harfenist et al. 1989). There is,however, no evidence linking NorthernLeopard Frog declines in Alberta to use of

19

pesticides or other toxic compounds. Research in Wisconsin also failed to establisha link between pesticide use and populationdeclines, although research has pointed out theneed for further study into the possible role ofherbicides in the decline (Hine et al. 1981).

The distribution of many amphibian species isrelated to the acidity of wetland habitats, andconcerns have been raised that acid rain couldlower the pH of wetlands causing populationdeclines in many species (Clark 1992). Laboratory studies have shown that wetlandacidification can lead to increased mortality inembryos and disrupt sodium and chloridebalances and increase the rate of heavy metaluptake in larvae (Clark 1992, Freda andMacDonald 1990, Freda et al. 1990). Decreased pH levels can also have indirecteffects by altering food chain dynamics andhabitat characteristics in wetlands (Clark1992).

Acid deposition is of greatest concern in theCanadian Shield in eastern Canada. To date,however there has been no data linkingpopulation declines relative to increasedhabitat acidity (Clark 1992, Corn 1994). Aciddeposition is of less concern in western NorthAmerica, and episodic acidification has beendismissed as a cause of Northern LeopardFrog declines in montane areas in Colorado(Corn et al. 1989).

10. Summary. - The cause of NorthernLeopard Frog population declines in Alberta isunknown. Initial population declines wentlargely unnoticed and in many areas were socomplete that there was little or noopportunity to examine the reason(s) for thedecline. Although little studied, populationdeclines in Alberta do not appear to be part ofa regular cycle. Instead, the declines appear tobe related to a singular, widespread factor

affecting the survival of the species(Cottonwood Consultants 1986, Koonz 1992,Powell and Russell 1996, Roberts 1981, 1987,1992, 1994, Vial and Saylor 1993).

The abrupt population declines observed inAlberta appear to follow a similar pattern ofabrupt and massive population die-offswitnessed over much of the species� range inthe upper midwestern states and prairieprovinces during the 1970s. Despiteinvestigations into the cause(s) of thesedeclines, the underlying causes remain amystery. Hine et al. (1975, 1981) conducteda three-year study to determine the cause ofthe massive population die-off observed inWisconsin in the early 1970s. The studyrevealed that there had been a dramaticreduction in Northern Leopard Frogpopulations across the state and that only asmall percentage of suitable ponds showedevidence of breeding activity. Despitediminished population densities, breedingphenology, sex and age ratios, size andcondition of adults and young, egg production,metamorphosis and movements appeared to benormal relative to other published studies. There was also no evidence of mortality at thebreeding ponds. Widespread mortality was,however, noted with the onset of colderweather in the fall. Low-levels of mortalitywere noted soon after frogs began to gather atoverwintering sites, and increased to a peakjust before freeze-up when the frogs wereentering the water for hibernation. There werealso some indications that mortality continuedthrough the winter. Winterkill, resulting fromoxygen depletion in the water column, wasdismissed as a cause of the mortality becausehigh incidences of mortality were observed atdeep (non-winterkill) lakes, along troutstreams and at spring fed ponds. Extensivepathological studies were conducted on sickand dying frogs. Laboratory observations

20

revealed a variety of internal and externalabnormalities including ventral skindiscoloration (�red leg�), hard muscles,eroded appendages, subcutaneoushaemorrhages, eye haemorrhages, bodyemaciation and various liver abnormalities. Histological examination of liver sectionsrevealed necrotic tissue similar to thatproduced by toxic accumulation. Many adultfemale frogs also had normally-developed, butunpigmented eggs, suggesting a diversion fromnormal oogenesis patterns or pathologicaloogenesis. Incidents of egg resorbtion werealso noted, as were incidents of unusualbehaviour. Specifically, frogs were observedcrawling out of the water onto ice, and deadfrogs were found on the ice of partially frozenlakes in November and December. Theseobservations lead Hine et al. (1981) to suggestthat frogs were possibly unable �to enter andremain in the water at hibernation time, whichin turn may be related to abnormal watermetabolism beneath the skin and the changefrom lung to skin respiration�.

The study failed to identify a specific cause forthe mortality observed in Wisconsin Based onthe technology available at the time, viral andbacterial infection were ruled out as majorcauses of mortality. Hine et al. (1981) notedthat there was a need for additional studies todetermine if pesticides, particularly theherbicide Atrazine, played a role in thedeclines. Population monitoring andlaboratory studies also failed to determine thecause of similar die-offs in Manitoba (Koonz1992). As in Wisconsin, mortality wasgenerally associated with conditions of �redleg�.

STATUS DESIGNATIONS

1. Alberta. - In 1984, the Northern LeopardFrog was listed as a �declining� species in

Alberta, and the goals of monitoringpopulation status and ensuring viablepopulations were established (Alberta Fish andWildlife 1984). In the following year, thespecies was categorized as �statusundetermined� in A Draft Policy for theManagement of Threatened Wildlife inAlberta (Alberta Fish and Wildlife 1985). Cottonwood Consultants (1986)recommended that the species be regarded as�threatened� in Alberta. Roberts (1987, 1991)suggested that Northern Leopard Frog wasendangered, requiring management to preventfurther declines and to aid in recovery. Because of concerns over widespreadpopulation declines in southern Alberta, theofficial status was upgraded in 1991 and theNorthern Leopard Frog was designated as a�Red List� species (Alberta Fish and Wildlife1991a). This status was reaffirmed in 1996(Alberta Wildlife Management Division 1996).

In 1991, a provincial status report wasprepared (Wershler 1991a). It recommendedthat the Northern Leopard Frog be designatedas a �threatened� species and that its legalstatus under the Alberta Wildlife Act bechanged from an �unlicensed [non-liscence]species�, which allowed for the collection orharvesting of the species but prohibitedexportation, buying or selling, to a �licensed[nongame] species� to afford the speciesprotection from collecting. A draft provincialmanagement plan was prepared in 1992(Seburn 1992c). The management planestablished the goal of maintaining or restoring�a minimum of 30 viable subpopulations in sixdrainage systems across the historic range inAlberta�. It also recommended that theNorthern Leopard Frog be designated as an�endangered� species under the AlbertaWildlife Act. In January 1997, the species wasdesignated as an �endangered species� underthe Alberta Wildlife Act.

21

2. Other Areas. - In British Columbia, theNorthern Leopard Frog was regarded as a�Blue List� species in 1991 (Seburn 1992c). Since then, the Leopard Frog has beenupgraded to the �Red List� of species whichare currently being considered for designationas �threatened� or �endangered� under theprovincial Wildlife Act (L. Fries, pers. comm.). No formal ranking system exists inSaskatchewan, but restrictions are in place toprevent human development in breeding areas(W. Harris, pers. comm.). In Manitoba, apermit is required for commercial collecting ofLeopard Frogs (Preston 1987). The NorthernLeopard Frog was identified as a �species ofconcern� in the Prairie Conservation ActionPlan (World Wildlife Fund Canada 1988).

The Northern Leopard Frog has currently notbeen assigned a designation by the Committeeon the Status of Endangered Wildlife inCanada (COSEWIC). A draft status reporthas recently been prepared for populations inwestern Canada (Seburn and Seburn 1996),and a status designation will be assigned in thenear future (C. Seburn, pers. comm.).

The Northern Leopard Frog has been placedon a candidate list of species of specialconcern by the State of Colorado (Livo 1986).

RECENT MANAGEMENT INALBERTA

1. Planning. - The planning of managementactivities for Northern Leopard Frogs has beenguided by the preparation of a provincial statusreport and draft management plan. The statusreport (Wershler 1991a) presented informationon the general ecology of the species, andcurrent and historic distribution and abundancedata, and outlined potential threats to Leopard

Frogs in the province. The draft provincialmanagement plan (Seburn 1992b) outlinedobjectives for population and habitatmanagement and for informing and educatingthe public about the plight and conservation ofthe Leopard Frog in Alberta. The report alsodiscussed the possible need to re-establishpopulations by transplanting individuals fromexisting populations to areas containingsuitable habitat.

The species was also considered as part ofplanning exercises conducted by the NorthAmerican Waterfowl Management Plan(NAWMP) in Alberta. It was ranked as apriority vertebrate species in relation toNAWMP program delivery in the prairie andaspen parkland biomes (Patriquin 1993).

2. Population Monitoring. - The Alberta Fishand Wildlife Division launched a postercampaign in 1989, which asked the generalpublic to report all sightings of NorthernLeopard Frogs. Over 150 reports werereceived in response to the campaign (Seburn1991, D. Seburn 1994, Wershler 1991a). Many of these reports turned out to be otherspecies, or were thought to be unreliableobservations (Wershler 1991a). Nevertheless,many of the reports led to the discovery ofnew population centres, proving the value ofthe program.

During 1991 and 1992, field surveys wereconducted to update and expand theinformation base on Leopard Frog habitats,populations and distribution in southernAlberta. Sightings reported during the postercampaign were also checked during the fieldprogram. In 1994, the Alberta AmphibianMonitoring Program was initiated (AlbertaFish and Wildlife 1994, Powell and Russell1996, Yaremko 1996). This program wasimplemented under the auspices of the

22

Declining Amphibian Population Task Forceestablished by the Species SurvivalCommission of the World ConservationUnion. The monitoring program was designedto gather basic presence/absence data onamphibians using volunteers. Volunteers areprovided with a handbook (Alberta WildlifeManagement Division, no date) and a tape ofcalls to assist with identification. To date,over 300 individuals have become involvedwith the program. Data obtained by thevolunteers have been, or will be, entered intothe Biodiversity/Species Observation Databasedeveloped by Alberta Natural ResourcesService. Confirmed observations from the1990 poster campaign as well as observationsfrom surveys sponsored by the Albertagovernment have also been entered into thedatabase.

3. Habitat Securement, Protection andEnhancement. - In 1991, a management planwas developed for the Prince�s Spring area,which contains a major breeding population ofNorthern Leopard Frogs (Wershler 1991b). The plan outlined the need for fencing aroundspring-fed streams to protect fragile riparianhabitats from cattle damage. The springsthemselves were fenced sometime before 1980(Hofman 1992). Revisions to the fencing planwere made in 1992 (Wershler 1992b) andfences were established around the streams in1992 (Hofman 1992).

The significant Leopard Frog habitat at SextonCreek in the Cypress Hills is located within theproposed Eagle�s Nest Ranch Natural Area(Biota Consultants 1992). Managementconsiderations for the proposed natural areainclude restricting livestock activity aroundwetlands to protect Northern Leopard Froghabitat (Biota Consultants 1992).

In the fall of 1994, a population of Northern

Leopard Frogs was discovered along a smallcreek (Drain K) extending from LonesomeLake to the Bow River about 8 km south ofBow City (D. Watson, pers. comm.). Portionsof the creek are dominated by small spring-fedwetlands, which may provide importantbreeding or overwintering habitat. Levelportions of the creek are also dominated bylarge cattail marsh complexes. Most of thecreek flows across the Circle E project, whichis being developed for waterfowl productionunder the NAWMP. Project developmentbegan in 1995 and management plans for theproject recognised the importance of the creekas Leopard Frog habitat. In 1996, crossfencing was erected across pastures borderingportions of the creek to prevent disturbance ofthe wetlands by cattle during the breedingseason (A. Balaski, pers. comm.).

4. Research. - In addition to the previously-discussed survey and monitoring programs,three research projects with applications forLeopard Frog management have beenconducted in recent years. Seburn (1993)examined the feasibility of using pondenclosures to assess growth rates of transplantand control populations of tadpoles. Themethodology was found, however to beinadequate because of high predation rates andlow growth rates within the enclosures. In1993, habitat use and YOY dispersal studieswere conducted at Sexton Creek (Seburn1994, Seburn et al., in press). The results ofthese studies were discussed previously. YOYdispersal and overwintering survivorship werealso studied at Sexton Creek in 1994(Yaremko 1994).

5. Repatriation of Northern Leopard FrogPopulations. - The recovery andre-establishment of Northern Leopard Frogpopulations over much of their former range insouthern Alberta will be dependent on the

23

dispersal of individuals from existingpopulations. However, we know very littleabout dispersal in Northern Leopard Frogs andit is therefore difficult to predict the extent towhich dispersal may lead to recolonization ofunoccupied areas of suitable habitat. It maywell be that the relative isolation of somepopulations may limit opportunities forpopulation expansion because of the inabilityof individuals to disperse to other areas(Roberts 1994). Furthermore, some areas ofsuitable habitat may now be unavailable forrecolonization because of habitat alterationsthat have eliminated dispersal corridors. Thismay be particularly true of large areas in theparkland, which are separated from theremaining breeding populations in the south bylarge expanses of dry upland habitat (Roberts1994). Re-establishment of Northern LeopardFrogs in many parts of their former range maytherefore be dependent on transplantingindividuals from major breeding populations insouthern Alberta (Cottonwood Consultants1986; Roberts 1987, 1991, 1992, 1994,Seburn 1992c, Wershler 1991a). Majorreview papers about the pros and cons of usingtransplants to re-establish amphibianpopulations are presented in Burke (1991),Dodd and Seigel (1991) and Reinert (1991).

Under a pilot reintroduction program,Northern Leopard Frogs were released at twosites in central Alberta (Roberts 1991, 1992). At both sites, frogs survived and reproducedfor several years following release (W.Roberts, pers. comm.). However, at one ofthe sites a winterkill event eliminated thepopulation. At the other site, in the upperNorth Saskatchewan River basin, thepopulation continues to flourish and ismonitored annually (W. Roberts, pers.comm.). The success of this initial releaseindicates that Northern Leopard Frogs canperhaps be re-established using frogs from

population centres in the southern part of theprovince.

6. Public Information and Education. -Several authors (Cottonwood Consultants1986, Quinn 1991, Roberts 1991, Seburn1992, Wershler 1991a) have outlined the needto inform and educate the public about theplight of the Northern Leopard Frog. Publicinformation programs are felt important forbuilding awareness about the plight of thespecies, for soliciting sighting and otherinformation from the public, for requestingassistance in protecting and maintaininghabitat, and for reducing activities such ascollecting which may be detrimental to frogpopulations.

In Alberta, the dissemination of publicinformation has included the poster campaigninitiated in 1989, the publication of a LeopardFrog brochure in 1991 (Alberta Fish andWildlife 1991b) and the establishment of theAlberta Amphibian Monitoring Program in1984 (Alberta Fish and Wildlife 1994, Powelland Russell 1996, D. Seburn 1994, Yaremko1994). In addition, an elementary schoolteachers� guide about the Northern LeopardFrog was prepared in 1995.

SYNTHESIS

Prior to 1980, the Northern Leopard Frog waswidely distributed and locally abundant overmuch of Alberta south of Edmonton. However, populations are now greatly reducedin number, and the range is limited mainly tothe lower reaches of the South Saskatchewanand Milk River drainage basins.

In Alberta, the cause(s) of the abrupt andwidespread population declines that occurredin the late 1970s and early 1980s remains amystery. Our lack of understanding about

24

causes of the declines is reason for concern. Even if populations were to recover, eithernaturally or through conservation initiatives,the species would have to be considered at riskuntil such time as the cause(s) of the decline isdetermined and addressed. Hine et al. (1981)aptly sum up the situation as follows: �Thedrama of the leopard frog decline that has beenunfolding over the past decade may provide avital insight into ecosystem health - it must notgo on unnoticed or unattended.�

Recent general population increases inSaskatchewan (W. Harris, pers. comm.,

Seburn 1992b) and Manitoba (Koonz 1992)provide some promise that Northern LeopardFrog populations will recover in Alberta. Natural recovery and re-establishment ofpopulations in formerly occupied area will bedependent on dispersal of individuals from theremaining breeding populations. We knowvery little, however about dispersal inNorthern Leopard Frogs and it is thereforedifficult to predict the extent to whichdispersal may lead to recolonization of suitablehabitat areas. Re-establishment in some areas,particularly the central parkland, may thereforebe dependent on transplanting individuals fromthe major breeding populations in southernAlberta (Cottonwood Consultants 1986,Roberts 1987,1991, 1992, 1994, Seburn1992c, Wershler 1991a ). Until such time asbroad-scale transplantation is feasible,continued surveys and monitoring of provincialpopulations will be necessary to ensure thatcurrent population distribution and trends inthe province are well understood.

25

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