Population densities of Golden-winged Warbler , … OB Vol 27...6 ONTARIO BIRDS APRIL 2009 reported as a possible, probable or con - firmed breeder in only five Ontario loca - tions,

ONTARIO BIRDS APRIL 2009

Population densities ofGolden-winged Warbler,Blue-winged Warblerand their hybrids, ineastern Ontario Assessment with standardized survey protocols and mapping using Geographic Information Systems (GIS)

Laura E. King*, Virginia J. Emery*, Raleigh J. Robertson, Rachel Vallender, Paul R. Martin(*Equal contributors)

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Golden-winged Warbler, male.Photo: Laurie Smaglick-Johnson

Golden-winged Warbler, female.

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IntroductionGolden-winged Warblers (Vermivorachrysoptera) have long fascinated birdersand ornithologists alike, due in part totheir flashy plumage, distinctive songs,and ability to hybridize with the closelyrelated Blue-winged Warbler (Vermivorapinus). The Golden-winged Warblerpopulation near the Queen’s UniversityBiological Station (QUBS) north ofKings ton, Ontario, has been the subjectof exten sive, ongoing study since 1997.However, researc hers have never system-atically surveyed tracts of land to esti-mate densities of Golden-winged andBlue-winged Warblers or their hybridsin the area. We present survey protocolsand results from populations at QUBS;these baseline data are crucial in order todevelop a long-term conservation strat-

egy for the declining Golden-wingedWarbler. Detailed population data fromQUBS also has the potential to act as acase study, providing an in-depth exam-ple of how abundances might changethrough time in other locations. Popula-tion surveys are particularly importantin light of current threats to Golden-winged Warblers that include theadvancing range of Blue-winged War-bler populations and habitat loss.

Distributions, habitat and ecology of Golden-winged and Blue-wingedWarblers

Golden-winged Warblers breed fromextreme southeast Saskatchewan, south-ern Manitoba and Minnesota, eastthrough southern Ontario and south-west Quebec, and south to Georgia

Golden-winged and Blue-winged pair. Photo: Laurie Smaglick-Johnson

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(Confer 1992, COSEWIC 2006; Figure1). They are Neotropical migrants, win-tering in a large area from southern Mex-ico, through Central America, to north-western South America (Mills in Cad-man et al. 1987a; Figure 1). The Blue-winged Warbler breeds from SouthDakota to Oklahoma to South Carolina,and into southern Ontario (Gill et al.2001; Figure 2). They winter from mid-Mexico through the coasts of CentralAmerica, and south to Panama (Mills inCadman et al. 1987b; Figure 2). Bothspecies breed in open, early successionalareas where most vegetation is less thanthree metres in height (Mills in Cadmanet al. 1987a, b, Hunter et al. 2001). Ter-ritories also contain deciduous trees used

as singing perches, and are often posi-tioned along a forested edge (Confer1992). Surrounding trees are essential forforaging on moth larvae and caterpillars(Confer 1992, Demmons 2000).

Golden-winged and Blue-wingedWarbler distributions have undergone aseries of changes with breeding rangeexpansions and contractions over the pastcentury or more (Hamer et al. 2005).These changes correlate closely with pat-terns of human land use and changes tomanagement practices (Confer et al.2003). Golden-winged Warbler distribu-tion expanded northward from theAppalachian region into Ontario in theearly 1900s, Manitoba and Saskatche wanas early as the 1960s, and Quebec in the

Breeding Range

Winter Range.

Breeding Range

Winter Range

Figure 1. Summer (breeding) range, shown inblue, and winter (non-breeding) range, shown inorange, of the Golden-winged Warbler.Source: Birds of North America

Figure 2. Summer (breeding) range, shown inblue, and winter (non-breeding) range, shown inorange, of the Blue-winged Warbler.Source: Birds of North America

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1970s (Hamer et al. 2005, COSE WIC2006). Blue-winged Warblers, historical-ly west of the Appalachians and south ofthe Great Lakes, began to expand north-ward beginning in the 1860s, and eventu-ally reached Minnesota, Ontario and thesouthern New England states (Mills inCadman et al. 1987b, Vallender in Cad -man et al. 2007b).

Conservation concernsGolden-winged Warblers are decliningacross most of their range in Canada andthe United States. Populations in Ontariohave declined by approximately 12% peryear during the past ten years (Gill 1997,Sauer et al. 2005), leading them to be clas-sified as Threatened by the Committee onthe Status of Endangered Wildlife inCanada and protected under the Speciesat Risk Act (COSEWIC 2006, 2007). InCanada, populations were grow ing until10 years ago, likely because of a north-eastward range expansion. Since thattime, the species has started to disappearfrom regions in the southernmost por-tions of Ontario (presumably due to thearrival of the Blue-winged Warbler andsubsequent hybridization; COSE WIC2006). Moreover, it has been suggestedthat the species may have reached theuppermost limits of suitable habitat with-in Ontario (K.V. Rosenberg pers. comm.).Considered in concert, these factors arelikely both contributing to why theincreasing trend in the province is nolonger occurring.

Loss of early successional habitat isthought to be the primary factor behind

range-wide Golden-winged Warblerdeclines (Smith et al. 1993, Confer andLarkin 1998); this is caused by theanthropogenic suppression of natural for-est fires (Hunter et al. 2001), and encour-agement of forest regrowth after distur-bance or abandonment. Evaluation andconservation of suitable habitat willtherefore be critical for slowing declinesof the Golden-winged Warbler. Anotherfactor in the decline of Golden-wingedWarblers may be nest parasitism by theBrown-headed Cowbird (Molothrus ater).Cowbird parasitism may be particularlyimportant in declines in the UnitedStates; the impact in Canada is largelyunknown (Confer et al. 2003, COSE -WIC 2006).

Hybridization is another cause forconcern. Blue-winged and Golden-wing -ed Warblers can mate to form two recog-nized types of hybrids, as well as a widerange of hybrids which are not easily clas-sified as either type, and are, therefore,classified as introgressed. The two mainhybrid types are designated by differentplumages and known as “Law rence’s” and“Brewster’s” (Brewster 1874, Parkes1951), so named because they were onceconsidered separate species (Lawrence’sWarbler and Brewster’s Warbler).

These hybrids are both rare in Ont -ario, with the Brewster’s hybrid foundmost often around the Niagara Escarp-ment and Oak Ridges Moraine, alongthe southern edge of the Canadian Shield,and in the Long Point area (Vallender andLeckie in Cadman et al. 2007). The Law -rence’s hybrid, the much rarer form, was

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reported as a possible, probable or con-firmed breeder in only five Ontario loca-tions, during the course of surveying forthe second Atlas of the Breeding Birds ofOntario (Cadman et al. 2007). Breedingwas reported as possible in one square inthe region of Waterloo, possible in twosquares and probable in one square in theregion of Hamilton, and confirmed at onelocation near Elgin, close to QUBS (Val-lender and Leckie in Cadman et al. 2007).

Although a sighting of one of theserare birds can be exciting, they signal agrowing problem for the persistence of

Golden-winged Warblers. As the Blue-wing ed Warbler’s range expands north-ward, hybridization between the specieshas been implicated in Golden-wingedWarbler declines. ‘Pure’ Golden-wingedWar bler genes can become extirpatedfrom local populations, a process termed“genetic swamping” (Gill 1997), althoughthese genes can also persist in the popula-tion within hybrids (Dabrow ski et al.2005). At present, there is no evidencethat hybrids are at a disadvantage com-pared to the parental species in this system(Vallender et al. 2007a), so numerically

Golden-winged Warbler nest. Photo: Laurie Smaglick-Johnson

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dominant Blue-winged War blersmay be able to ‘swamp out’ Gold-en-winged Warblers after a shortperiod of contact.

However, given that gene flowis bidirectional between thesespecies (Shapiro et al. 2004,Dabrowski et al. 2005), it shouldbe noted that the mechanism bywhich Blue-winged Warblersreplace Golden-winged Warblers in areas of contact remains largelyunknown (Vallender et al. 2007b).Over the past century, the Blue-winged Warbler has replaced theGolden-winged Warbler in sub-stantial regions of its historicbreeding range, especially at lowerelevations west of the AppalachianMountains and in the area to thesouth of Lake Ontario and LakeErie (Dabrowski et al. 2005, Ham -er et al. 2005). Establishment ofBlue-winged War bler populationsusually coincides with decreases in

local Golden-winged War b ler popula-tions, with complete replacement typi-cally occurring within 50 years of Blue-winged Warbler arrival (Gill 1980, 1987,1997). The only known site where thishas not yet occurred is in New York State,where the two species have co-existed forover 100 years (Confer and Tupper2000).

Though interactions with Blue-wing -ed Warblers may play a large role in thedecline of Golden-winged Warblers, therelative contribution of competition ver-sus hybridization to the declines remains

unknown (Gill 1997, Vallender et al.2007b). In addition, the relative impor-tance of Blue-winged Warblers amidother factors, such as habitat loss and par-asitism, in Golden-winged Warblerdeclines remains poorly understood andappears to depend on the geographiclocation of the population (COSEWIC2006). Habitat loss is severe in someareas yet nonexistent in other areas wherethe species is nevertheless declining (J.L.Confer pers. comm.); Blue-winged War-blers are absent from some decliningGolden-winged Warbler populations,and the prevalence of nest parasitismvaries across the range (Confer et al.2003, COSEWIC 2006).

Golden-winged Warblers and Blue-winged Warblers in Ontario

Golden-winged Warbler males begin toarrive in Ontario in early May, and arefollowed thereafter by females, who breedbetween early June and mid-July (COSE -WIC 2006). In southern Ont ario, Gold-en-winged Warblers have shown recentdeclines and range contractions whichhave been paralleled by a northwardexpansion of the Blue-winged Warblerinto many areas of southern and easternOntario (Mills inCadman et al. 1987a,b,Vallender in Cadman et al. 2007 a,b).Hybridization occurs in all areas wherethese two species come into contact (Gill1997).

The Golden-winged Warbler’s Ont -ario range spans from the northern shoreof Lake Erie near London, to the eastern

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edge of Lake Ontario near Kingston northto Ottawa, Sudbury and Spanish, includ-ing the Bruce Peninsula. Separate fromthis area, there is a small group south ofKenora near Lake of the Woods (COS E - WIC 2006). An estimated 18.2% of theglobal population of Golden-winged War -b lers (estimated at 105,000-270,000breeding pairs) reside in Ont ario eachbreed ing season, with the major ity ofthese birds concentrated in southern Ont ario (Vallender in Cadman et al.2007a, K.V. Rosenberg, pers. comm.).Blue-winged Warblers are now distributedthrough out much of southern Ont ario, asfar north as the east shore of Georgian Bay(Vallender in Cadman et al. 2007b). Ini-tially recorded in Ontar io in the early1900s, Blue-winged Warblers were con-firmed to be breeding by the 1950s andthe species has been increas ing in localabundance since then (McCracken 1994,Vallender in Cadman et al. 2007b). Blue-winged Warblers were confirmed to bebreeding at QUBS in 2005 (R. Vallenderunpublished data), but likely first arrivedin the late 1980s, albeit in very low num-bers (Weir 1989, R.J. Rob ert son and T.Demmons unpublished data).

Studies at Queen’s University Biological Station

The Golden-winged Warbler populationof approximately 200 breeding pairs nearthe Queen’s University Biological Station(QUBS) north of Kingston (44°34N,76°19 W, Leeds & Grenville and Fron-tenac Counties) has been extensively stud-

ied since 1997. These studies have provid-ed excellent long-term breeding, demo-graphic and genetic data, some of the bestavailable for the species. Investigationshave ranged from nesting habitat, sitefidelity, feeding behaviour, repro ductiveperformance, migratory origins, plumageand genetic relationships bet ween Gold-en-winged and Blue-winged Warblers(Demmons 2000, Paquin 2006, Reed etal. 2007, Vallender et al. 2007a,b, Fraseret al. 2008, McKinnon and Rob ertson2008, Neville et al. 2008). This extensiveresearch has required males to be colour-banded for individual identification.These banding efforts provide an excellentopportunity for surveys such as ours,allowing us to use colour band sightings toconfirm auditory point count observa-tions and differentiate between males onneighbouring or overlapping territories.

The study sites at QUBS are within thehybrid zone, yet right at the northern,expanding edge of the Blue-winged War-bler distribution. The northernmosthybrids in Ontario have been foundapproximately one hundred kilometresnorth of our study sites, west of Ottawa(Vallender and Leckie in Cadman et al.2007). This is an area of recent, yet active,hybridization (Vallender et al. 2007b).

Given the historical and continuingexpansion of Blue-winged Warblersnorth ward, there is a need to documentchanges in Blue-winged Warblers andtheir hybrids in terms of their relative andabsolute abundance, habitat use, andbreeding sites at QUBS, as well as at othersites in Ont ario.

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No Blue-winged Warblers or hybridswere detected on QUBS land whenresearch began in 1997 (T. Demmonsunpub lished data) and were not thoughtto be present in the area (Weir 1989), yetone or two Brewster's hybrids were pres-ent in 1991 and an introgressed Blue-winged Warbler hybrid was found onQUBS property from 1991-1993 (Martinand Robertson 1994). With continualstudy, the arrival of Blue-winged Warblersand increasing numbers of hybrids at thissite have been documented. The popula-tion at QUBS provides the unique chanceto follow a population from its initiallypure Golden-winged Warbler demo-graphic through to the predicted completeturn over to pure Blue-winged Warbler,monitoring hybrid iz a tion throughout.

Our investigation aimed to estimatepopulation densities of Golden-wingedWarblers, Blue-winged Warblers and theirhybrids (Brewster’s, Lawrence’s and intro-gressed) for the first time in a systematicway on QUBS property. This providedbaseline data that can be used in long-termmonitoring of population densities,hybridization and habitat use of thesespecies. We also colour banded new malesto allow continued estimates of returnrates for this population. By surveyingthree different areas containing a variety ofsuccessional land types, we can followpopulation shifts with habitat changesthat include both loss and gain of suitablehabitat. These baseline data will allowresearchers to document future changes inpopulations around QUBS. This projectholds incredible potential to inform con-

servation and management plans acrossthe Golden-winged Warbler range, espe-cially in Ontario.

MethodsSurvey sitesOur three survey sites were chosen basedon their previous roles in Golden-wingedWarbler studies at QUBS, confirmedbreeding pairs and varying degrees of suc-cession.

The Pangman Conservation Reservenear the village of Chaffey’s Lock, is oneof the central QUBS properties and hasbeen used for a variety of wildlife studiesfor many years, including multiple Gold-en-winged Warbler projects mentionedearlier. The Pangman survey area meas-ured 152 ha, or 1.52 km2. The area con-tained five large marsh areas, one lake, anda portion of a second lake, with largeforested areas and localized open habitat.The terrain was generally flat and oftenwet, and common plant species includedwhite ash (Fraxinus americana) and com-mon prickly-ash (Zanthoxylum ameri-canum) (V.J. Emery and L.E. King unpub -lished data).

The Massassauga Tract is a largeproperty south of the town of Westport.Approximately one-third of Massassaugawas surveyed, for a total area of 220 ha, or2.20 km2. This section was chosen as itwas most accessible by road, includedareas where Golden-winged Warblers hadbeen detected in previous years, and con-tained additional open areas which couldpotentially provide suitable habitat. Theproperty consists of a mix of mature

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forest and grassy areas, with occasionalpatches of scrub. The terrain is generallydry, very rocky with hills and small cliffs,and several small marshes in the southernsection. Common plant species were sim-ilar to those in the Pangman area.

The Bracken Tract is a large water-front property south of the town of West-port, and west of the town of Newboro.We surveyed the entire mainland sectionof the tract (204 ha, or 2.04 km2) becauseprevious research found many Golden-winged Warblers here, especially in thewestern areas. The tract consists largely ofabandoned farmland with active seasonalcattle grazing in the eastern portion andlarge but fragmented forest sections. Theterrain is generally even with someexposed portions of flat rock, one pond,and one large central wetland, in additionto several smaller marshes. Commonplant species included meadowsweet(Spiraea spp.) and common milkweed(Asclepias syriaca).

Previous surveysWe include bird counts from 2006 and2007 in our discussion. In these years,surveys were conducted by visiting siteswith apparently suitable habitat and areasthat were known to be occupied by Gold-en-winged Warblers in previous years(Paquin 2006, H.J. Munro pers. comm.).During these years, song playback wasused inconsistently and did not adhere toa standardized protocol. The methodused here involved consistent playbackand complete surveying, and thus shouldprovide better detection and more obser-

vations even if the population is decreas-ing. For these reasons, and because theprotocols in previous years did notinclude a way to test for the absence ofbirds in an area, comparisons betweenyears are for interest only. Continued useof the formalized protocols of 2008 willallow informative comparisons withfuture surveys.

Measuring population densities canprove difficult as it is necessary to ensurethat every individual is counted onlyonce. Therefore, to improve accuracy wecombined (i) colour banding for individ-ual identification, (ii) comprehensive sur-vey methods including both auditory andvisual techniques and (iii) GeographicInformation Systems (GIS) to help max-imize coverage of plots, analyze surveyresults and map locations of focal males.

Visual confirmation of birdsWe recorded band combinations of pre-viously banded birds and attempted toband all males without bands using bothaluminum numbered Canadian WildlifeService (CWS) bands and coloured plas-tic bands. Maintaining a banded popula-tion is essential for determining returnrates of birds and improving estimates ofpopulation changes. Keeping a record ofbanded bird locations also ensured nobirds were counted twice during the sur-vey, and confirmed species identificationas Golden-winged, Blue-winged, orhybrid warblers with close inspec tion inthe hand. Birds banded in 2008 haveband combinations starting with BS, orblue and silver bands on the left leg.

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Playback designThe survey playback was based on amonitoring protocol developed by theCornell Lab of Ornithology Conserva-tion Science Department. The playbackhas four elements: silence, type 1 andtype 2 Golden-winged Warbler songs(Con fer 1992), and a recording of Black-capped Chickadees (Poecile atricapillus)mobbing a singing Eastern Screech–Owl(Megascops asio). Type 1 songs functionprim arily to attract mates and for speciesrecognition (different for the twospecies), and type 2 songs are used in ter-ritory defense (shared by both species)(Spector 1992). Blue-winged Warblersand hybrids also responded to type 2song of Golden-winged Warbler (as pre-viously observed in Murray and Gill1976). We used all four of these elementsto ensure that as many male birds as pos-sible were detected. Females cannot bereliably surveyed as they will not consis-tently respond to playback or to mob-bing, so only males are included inresults.

For efficiency, we shortened the play-back at alternating survey points from18 minutes (long playback) to 10 min-utes (short playback) (Table 1). We alsotested the detection ability of playbackto verify our survey methodology.Although the shorter protocol was notperfect at detecting birds, we minimizederror with multiple visits to survey sites,along with visual identification of colourbanded birds to confirm auditory detec-tion. Additionally, the shorter playback

is the same length or longer than previ-ous survey playbacks that have beenshown to be effective (e.g., 3 minutes ofplayback, 6 minutes of total observation,Kubel and Yahner 2007; 3 minutes ofplayback, 7 minutes of total observation,Martin et al. 2007).

Minute Playback type Playback type (long protocol) (short protocol)

1 Silence Silence

2 Silence Silence

3 Silence Silence

4 Type 1 Type 1

5 Type 1 Type 1

6 Type 1 Type 1

7 Type 1 Silence

8 Type 1 Type 2

9 Silence Type 2

10 Type 2 Silence

11 Silence

12 Mobbing

13 Mobbing

14 Mobbing

15 Mobbing

16 Mobbing

17 Silence

Table 1. Playback design for detectingGolden-winged Warblers, showing thesequence of playback components forlong (17 minutes) and short (10 minutes)survey protocols.

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Survey point count layoutPrevious work has shown that Golden-winged Warbler songs can be detected ata maximum distance of 100-150 metersfrom their territories (Kubel and Yahner2007) or even as far as 200 metres in someareas (K.V. Rosenberg pers. comm.).However, based on field experimentationof hearing distances in our study area, weconcluded that a 100-meter radius circlewas most appropriate and placed a circleof this size around each point count torepresent the area surveyed. Any birdswith territories within each circle shouldbe heard or seen from the survey point.Birds whose territories occupied morethan one circle were unlikely to be count-

ed twice because we visually confirmedcolour band combinations of bandedbirds for most of our detections.

A total of 142 point counts was con-ducted. We focused our efforts on threetracts of QUBS land that have had knownGolden-winged Warbler territories in thepast two years [Pangman (38 points),Massassauga (53 points) and Bracken (51points)]. Using GIS software (ArcGIS9.2, ESRI, Redlands, California, USA),we set out a grid of points separated by200 meters in all directions to preventsurvey overlap. We assigned alternatinglong and short protocols to each of thesesurvey points.

Figure 3. Distribution of birds shown by band combinations, and results of point counts shown by surveyradii, within the Pangman Conservation Reserve, near Chaffey’s Lock, ON, Queen’s University BiologicalStation (QUBS). The purple outline represents the property boundary. All band combinations representGolden-winged Warblers.

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Survey protocolSurveys were conducted between 04:30and 11:00h, between 10 May and 20 June2008. Every-other survey point on every-other transect (1/4 of all points) was vis-ited twice within the survey period, andevery survey point was visited at least oncebetween 25 May and 20 June 2008.

Using a handheld Global PositioningSystem (GPS) unit (GPSMAP 60Cx,Garmin International, Olathe, Kansas,USA) we hiked to each of the surveypoints, recorded the latitude and longi-

tude coordinates of eachfield site, and followed thedesignated playback pro-tocol for that point count.When a point was inacces-sible (in the middle of alake or deep swamp) thepoint on the shorelinewhich was closest to theoriginal point was usedinstead. We recorded theminute of detection for all

birds seen and heard during the protocol,as well as those birds seen or heard afterthe protocol had ended and upon subse-quent visits.

Mapping survey resultsWe created the precise maps of Figures 3,4, and 5 showing survey results and thelocations of each male bird using GISsoftware (ArcGIS 9.2, ESRI, Redlands,California, USA). These maps include thefollowing data; (1) The UTM (UniversalTransverse Mercator) coordinates in Zone

Figure 4. Distribution of birdsshown by band combinations,and results of point countsshown by survey radii, within theMassassauga Tract, near New-boro, ON, Queen’s UniversityBiological Station (QUBS). Purpleoutline represents the propertyboundary. All band combinationsrepresent Golden-winged Warblers. Note that two bandcombinations (BSGY and OWYS)are repeated on the map, asthese males changed territoriesduring the field season. See Figure 3 for complete legend.

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18 along the map borders(the same coordinatesused to locate sites byGPS); (2) landscape infor -m ation, including forest-ed, open, wetland andaquatic habitat; (3) circlesrepresenting the approxi-mate area in which birdscould be detected whenobservers were at the cen-tre of the circle completing the protocols,coloured according to the number ofbirds detected; (4) the locations of birds,marked as a band combination, unband-ed Golden-winged Warbler (GWUB), orGolden-winged Warblers for which bandcombinations were unknown (NOID).As there were discrepancies betweenauditory and visual identifications (eg:some birds were heard twice), all densi-ties were calculated using the visual iden-tifications.

ResultsIn the 5.76 km2 surveyed at intervals of200 metres, we found 30 Golden-wingedWarblers, one Blue-winged Warbler,three Brewster’s hybrids and zeroLawrence’s hybrids, for a total of 34 birdsacross all areas. The mapped results ofsurveys conducted in Pangman, Massas-sauga and Bracken are presented in Fig-ures 3, 4 and 5 respectively.

Figure 5. Distribution of birdsshown by band combinations,and results of point countsshown by survey radii, within theBracken Tract, near Newboro,ON, Queen’s University Biologi-cal Station (QUBS). Purple out-line represents the propertyboundary, which for this tractdelimited the survey area. Blackband combinations representGolden-winged Warblers, blueband combinations representBlue-winged Warblers and redband combinations represent thehybrid Brewster’s Warbler. SeeFigure 3 for complete legend.

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General observationsMales usually responded well to playbackand mobbing, becoming visibly agitatedwhile approaching the speaker. Playbackseemed more useful earlier in the breed-ing season, and mobbing more effectivelater in the season. This may result frommales aggressively defending territories inthe beginning of the season, then defend-ing their mate and perhaps offspringfrom a perceived predator later in the sea-son during nesting.

Golden-winged Warblers often nestin aggregations of as many as ten pairs(Confer and Knapp 1981, Vallender inCadman et al. 2007a), and we oftenfound several males within the samesmall area. This is well illustrated in Fig-ure 4 (the southwest corner of the surveyarea of Massassauga) and Figure 5 (mostbirds located in Bracken were in closeproximity to each other). This could be aresult of the birds clustering at suitablehabitat patches (Vallender in Cadman etal. 2007a), as the open habitat, whenpresent, is often large enough to supportseveral adjacent territories. PangmanConservation ReserveSix male Golden-winged Warblers werefound in the surveyed area (Figure 3), adensity of 0.039 per ha. Of these, webanded one, three had been banded inprevious years, one remained unbanded,and one was unidentified as to whether ornot it was banded. The densities of Blue-winged Warblers and hybrids were zero.

Massassauga TractSix male Golden-winged Warblers werefound in the surveyed area (Figure 4), adensity of 0.027 males per ha. Of these,we banded one, four had been banded inprevious years, and one remained unban -ded. The densities of Blue-winged War-blers and hybrids were zero.

Bracken TractEighteen male Golden-winged Warblerswere discovered during surveying (Figure5). Of these, we banded ten, four hadbeen banded in previous years, two wewere unable to band, and two wereuniden tified as to whether or not the birdwas banded. This represents a density of0.088 males per ha. One Blue-wingedWarbler and three hybrid (Brewster’s)males were found, and we banded all fourof these birds.

DiscussionIn total, we detected 30 Golden-wingedWarblers, one Blue-winged Warbler,three Brewster’s hybrids, and zeroLawrence’s hybrids during our surveys inthree separate areas on QUBS property(Figures 3-5). This represents a total of 34male birds across an area comprising 5.76km2, representing an overall density of0.052 male Golden-winged Warblers perha, 0.0017 male Blue-winged Warblersper ha, and 0.0052 male hybrids per ha.

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Geographic ResourcesWe used GIS software and GPS units inorder to visualize large-scale patterns andcollect precise and informative data in thefield. Previously, surveyors navigated tobird territories with the aid of landmarks,descriptions, and approximate visualmeasurements, which may change withtime. For repeatability, all point countlocations were GPS marked and surveyorswill be able to locate this point exactly infuture years. In addition to helping rec-ognize patterns such as the distribution ofmales over certain areas of cleared orforested land, the precision of GIS tech-nologies is essential to monitoring popu-lation changes in such late successionalspecies that may show only subtle shifts inhabitat use over many years. We are con-fident that GIS and GPS technologies willbe central to precisely measuring futureshifts in Golden-Winged Warbler habitatuse.

Pangman Conservation ReservePangman (Figure 3) had an intermediatedensity of Golden-winged Warblers at0.039 males per ha, slightly below theoverall average across the three areas.

In 2006 and 2007, twelve and tenmale Golden-winged Warblers, respec-tively, were found within this study area,even without the use of a standardizedsurvey protocol. We had expected to findhigher numbers in 2008 when surveyingwith a standard protocol for the first time,but were surprised to find fewer birds. Ifthis trend continues in future years, it maysuggest that the advancing succession in

this area is reducing the suitability of thehabitat for Golden-winged Warblers.Blue-winged Warblers and hybrids havenot been reported within this area in thepast two years, but it is noteworthy that arare Lawrence’s hybrid was sighted in2006 just adjacent to this area, that hasbeen undetected by researchers in the pasttwo years.

Massassauga TractMassassauga (Figure 4) had the lowestdensity of Golden-winged Warblers at0.027 males per ha, approximately one-half of the average density across the threeareas. Land cover on this tract appearedeither too mature (tall, closely spacedtrees) or not mature enough (open, grassyfields devoid of shrubs) with fewer areasin the in-between stages that are suitablefor Golden-winged Warblers than theother tracts (V.J. Emery and L.E. Kingunpublished data). Additionally, gradualand shrubby edges of forests are thoughtto be important to the nesting success ofGolden-winged Warblers (Demmons2000). We noticed that most forest edgesat Massassauga were more abrupt thanthose found at Bracken, and hypothesizethat the edge habitat in Massassauga issuboptimal, an idea we will explore withfuture vegetation studies.

Interestingly, two males in this areashowed territory shifts within this same2008 season (BSGY and OWYS, Figure4). This underscores the importance of abanded population, as the shifts wereimmediately confirmed in the field, andwe avoided counting each bird twice.

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In 2006 and 2007, one and four maleGolden-winged Warblers, respectively,were detected within the surveyed areasof the Massasauga Tract, along with twomale Brewster’s hybrids in 2006 and onemale Blue-winged Warbler in 2007(Paquin 2006, H.J. Munro pers.comm.). The increase in the number ofGolden-winged Warblers found in 2008likely reflects the much larger area sur-veyed, including discovery of several newterritories, and the use of standardizedprotocols.

Bracken TractBracken (Figure 5) had the highest den-sity of all surveyed areas at 0.088 Gold-en-winged Warbler males per ha. It wasalso the only area in which Blue-wingedWarblers and hybrids (Brewster’s) werefound, with one and three males sighted,respectively. The presence of a Blue-winged Warbler and hybrids may simplyresult from higher overall densities ofbirds, including Golden-winged War-blers, in this area. Bracken may representhabitat most suitable for Golden-wingedWarblers, as active cattle grazing in theeastern portion has helped to maintainan early successional state over manyyears (QUBS 2004).

In 2006 and 2007 respectively, tenand seventeen male Golden-winged War-blers were found within the surveyedareas of the Bracken Tract, along with onemale Brewster’s hybrid in 2006 and onemale Blue-winged Warbler in 2007(Paquin 2006, H.J. Munro pers.comm.). The increased numbers in 2008

likely reflects surveying throughout theentire tract as opposed to only certainsections.

Golden-winged Warbler DensitiesGolden-winged Warbler densities haverarely been reported in the literature, butrange from 0.55 males per ha in an areacomprising only seedling trees, to 0.04males per ha for an area with saplings andmedium-sized aspen (Roth and Lutz2004). Given that Golden-winged War-bler territories can be as large as two oreven five hectares (Confer 1992), the firstdensity (0.55) represents an extremelyhigh concentration of male birds, morethan five times the highest density foundin this study (0.088 males per ha atBracken). Other densities have beenreported as males per station, with thehighest being 0.79, or approximately0.20 males per ha (calculated from Mar-tin et al. 2007). Since all of Bracken is notentirely suitable habitat for Golden-winged Warblers, our intermediate esti-mates of density seem reasonable.

However, we still do not knowwhether all suitable habitat on QUBSproperty is currently occupied by Gold-en-winged Warblers. Additionally, thedetection of all male birds in a given areais generally not possible (Thompson2002); detection probabilities can varywidely, including with habitat (Kubeland Yahner 2007), which differed great-ly across our study areas. Previous workwith Golden-winged Warblers hasdemonstrated that detection can beextremely difficult, even when close to an

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active nest (Confer et al. 2008). While weattempted to address this issue withrepeated sampling, and a survey protocolwhich included both song playback andmobbing, it is nevertheless important toacknowledge that our counts likely didnot include every male bird, and, there-fore, our calculated densities representour best estimates.

Early successional habitatsGolden-winged and Blue-winged War-blers specialize in using early successionalland such as old farm fields (Litvaitis2003, Vallender in Cadman et al. 2007).Species such as these which rely on openareas have declined more than thosefound in mature forests (Askins 1993,2000, Rich et al. 2004, Cadman et al.2007), often due to habitat loss, whetheranthropogenic or natural (the inevitableprocess of succession). Anthropogenichabitat loss is likely a problem for speciessuch as the Golden-winged Warbler, asthe Atlas of the Breeding Birds of Ontarioshows “rural non-farm” areas, such asabandoned farms, have been decreasingsince approximately 2001 in areas southof the Canadian Shield, where the Gold-en-winged Warbler is concentrated (Cad-man et al. 2007).

Compounding this problem, naturalhabitat loss also contributes to declines.Since the Golden-winged Warbler relieson an inherently ephemeral early stage ofsuccession, habitat maintenance is a chal-lenge because appropriate habitat rapidlyprogresses to forest if intervention is notimplemented (Hamer et al. 2005). To

maintain suitable early successional habi-tat, disturbances such as timber harvest-ing, grazing, or periodic use of fire, needto be reinstated, requiring active manage-ment (Confer 1992, Klaus and Buehler2001, Roth and Lutz 2004). Anothermanagement approach is leaving gradualor soft edges to hayfields, which canincrease the suitability of habitat for nest-ing sites (Demmons 2000).

At our study sites, many of the openfields of Massassauga are mowed annual-ly for hay, leaving ‘sharp’ edges, while inBracken, open areas are maintained bylate-summer grazing by cattle, leavingmuch more ‘gradual’ edges, which appearto better support Golden-winged War-blers. These types of simple modificationsto agricultural practices and managementcould affect habitat suitability for Gold-en-winged Warblers.

When management plans such asthese are put into place, careful monitor-ing will be needed to ensure that the man-aged habitat is fulfilling the needs of thesedeclining shrubland species. Our resultswill serve as a baseline for this type ofmonitoring at QUBS and contribute tothe Golden-winged Warbler conservationinitiatives currently underway across thebreeding range of the Golden-wingedWarbler.

To meet this challenge of monitoringGolden-winged Warblers, the help ofamateur and professional field ornitholo-gists and birders is more important thanever. With limited resources, professionalornithologists cannot survey the amountof land required to follow population

VOLUME 27 NUMBER 1

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changes across the entire province. TheAtlas of the Breeding Birds of Ontario wasone of our greatest resources in identify-ing trends, and the level of detail provid-ed in the most recent Atlas allowed us tocompare changes in populations in theareas around our survey sites. The impor-tance of this information cannot be over-stated, and we hope that in the future fieldornithologists and birders will continue tomonitor bird species, especially thosewhich are declining and most in need ofour attention.

To help monitor Golden-winged War-blers, Blue-winged Warblers, and threeother declining migratory songbirds, sub-mit your sightings to Priority MigranteBird coordinated through Cornell Lab ofOrnithology at www.ebird. org//primig.Finally, if birding in an area where ourstudies have taken place, please reportcolour banded warblers to the NorthAmerican Bird Banding Program athttp://www.pwrc. usgs.gov/bbl/ or call 1-800-327-BAND (2263), and help play apart in the crucial long-term monitoringof these threatened species.

Acknowledgements

We thank Frank Phelan, Floyd Connor, FrancesBonier, Martin Piorkowski, Mark Conboy, andall members of Paul Martin’s Lab for assistancewith research at QUBS. Thanks to our externalreviewer for manuscript comments. Fundingprovided by an NSERC grant to PRM and RJR,and the J. Allen Keast Research Fellowship toLEK and VJE.

Literature Cited

Askins, R.A. 1993. Population trends in grass-land, shrubland, and forest birds in easternNorth America. Current Ornithology 11:1-34.

Askins, R.A. 2000. Restoring North America'ssongbirds. New Haven, Connecticut: Yale University Press.

Brewster, W. 1874. A new species of NorthAmerican warbler. American Sportsman 5:33.

Cadman, M.D., P.F.J Eagles and F.M.Helleiner (eds.) 1987. Atlas of the BreedingBirds of Ontario. Federation of Ontario Naturalists and Long Point Bird Observatory.Waterloo: University of Waterloo Press.

Cadman, M.D., D.A. Sutherland, G.G.Beck, D. Lepage and A.R. Couturier (eds.),2007. Atlas of the Breeding Birds of Ontario,2001-2005. Bird Studies Canada, Environ-ment Canada, Ontario Field Ornithologists,Ontario Ministry of Natural Resources, andOntario Nature, Toronto.

Confer, J. L. 1992. Golden-winged Warbler(Vermivora chrysoptera), The Birds of NorthAmerica Online (A. Poole, ed.). Ithaca: CornellLab of Ornithology; Retrieved from the Birdsof North America Online:http://bna.birds.cor-nell. edu/bna/species/020doi:10.2173/bna.20

Confer, J.L. and J.L. Larkin. 1998. Behav-ioral interactions between Golden-winged andBlue-winged warblers. Auk 115:209-214.

Confer, J.L. and K. Knapp 1981. Golden-winged Warblers and Blue-winged Warblers:The relative success of a habitat specialist and a generalist. Auk 98:108-114.

Confer, J.L. and S.K. Tupper. 2000. A reassessment of the status of Golden-wingedand Blue-winged Warblers in the HudsonHighlands of Southern New York. Wilson Bulletin 112:544-546.

Confer, J.L., J.L. Larkin and P.E. Allen.2003. Effects of vegetation, interspecific comp -et ition, and brood parasitism on Golden-wing -ed Warbler nesting success. Auk 120:138-144.

20


Confer, J.L., R. E. Serrell, M. Hager, and E. Lahr. 2008. Field tests of the Rosenberg-Blancher method for converting point countsto abundance estimates. Auk 125:932-938.

COSEWIC 2006. COSEWIC assessment andstatus report on the Golden-winged WarblerVermivora chrysoptera in Canada. Committee onthe Status of Endangered Wildlife in Canada.Ottawa. (www.sararegistry .gc.ca/status/ status_e.cfm).

COSEWIC 2007. Canadian Species at Risk.Committee on the Status of EndangeredWildlife in Canada, September 2007.

Dabrowski, A., R. Fraser, J.L. Confer and I.J. Lovette. 2005. Geographic variability inmitochondrial introgression among hybridizingpopulations of Golden-winged (Vermivorachrysoptera) and Blue-winged (V. pinus) Warblers. Conservation Genetics 6:843–853.

Demmons, T.D. 2000. Nest site selection andnest predation patterns at forest-field edgesM.Sc. Thesis. Department of Biology, Queen’sUniversity, Kingston ON.

Fraser, K. C., T. K. Kyser, R. J. Robertsonand L. M. Ratcliffe. 2008. Seasonal patterns inhydrogen isotopes of claws from breedingwood-warblers (Parulidae): utility for estimat-ing migratory origins. Avian Conservation andEcology - Écologie et conservation des oiseaux3:2.

Gill, F.B., Canterbury R.A. and J L. Confer.2001. Blue-winged Warbler (Vermivora pinus),The Birds of North America Online (A. Poole,ed.). Ithaca: Cornell Lab of Ornithology;Retrieved from the Birds of North AmericaOnline: http://bna.birds.cornell.edu/ bna/species/584

Gill, F. B. 1980. Historical aspects of secondarycontact and hybridization between Blue-wingedand Golden-winged Warblers. Auk 97:1-18.

Gill, F.B. 1987. Allozymes and genetic similari-ty of Blue-winged and Golden-winged Warblers. Auk 104:444-449.

Gill, F.B. 1997. Local cytonuclear extinction ofthe golden-winged warbler. Evolution 51: 519-525.

Hamer, P.B., K.V. Rosenberg and D.A.Buehler. 2005. Is Management for Golden-winged Warblers and Cerulean Warblers Com-patible? USDA Forest Service Gen. Tech. Rep.PSW-GTR-191

Hunter W.C., D.A. Buehler, R.A. Canter -bury, J.L. Confer and P.B. Hamel. 2001.Conservation of disturbance-dependent birds ofeastern North America. Wildlife Society Bul-letin 29: 440–455.

Klaus, N.A. and D.A. Buehler. 2001. Golden-winged Warbler breeding habitat characteristicsand nest success in clearcuts in the southernappalachian mountains. Wilson Bulletin 113:297-301.

Kubel, J. and R. Yahner. 2007. Detectionprobability of Golden-winged Warblers duringpoint counts with and without playback record-ings. Journal of Field Ornithology. 78:195-205.

Litvaitis, J.A. 2003. Shrublands and early-suc-cessional forests: critical habitats dependent ondisturbance in the northeastern United States.Forest Ecology and Management 185:1-4.

Martin, P.R. and R.J. Robertson. 1994.Effects of forest management practices andforestcutting history on the songbird communi-ties of mature hardwood forest stands, LakeOpinicon, Leeds/Frontenac Cos., Ontario.Eastern Ontario Model Forest Program. 190pp.

Martin, K.J., R.S. Lutz and M. Worland.2007. Golden-winged Warbler habitat use andabundance in northern Wisconsin. WilsonJournal of Ornithology 119:523-532.

McCracken, J.D. 1994 Golden-winged andBlue-winged Warblers: their history and futurein Ontario. Pp 279-289 in Ornithology inOntario. Spec. Publ. No. 1. M.K. McNicholland J.L. Cranmer-Byng, eds. Ontario FieldOrnithologists. Hawk Owl Publishing, Whitby,Ontario.

McKinnon, E.A. and R.J. Robertson. 2008.The signal function of a melanin-basedplumage ornament in Golden-winged Warblers.Wilson Journal of Ornithology 120: 366-370.

21

VOLUME 27 NUMBER 1

Mills, A. 1987a. Golden-winged Warbler, pp.358-359 in Cadman, M.D., Eagles P.F.J, andF.M. Helleiner (eds). Atlas of the BreedingBirds of Ontario. Federation of Ontario Natu-ralists and Long Point Bird Observatory. Uni-versity of Waterloo Press, Waterloo, Ontario.

Mills, A. 1987b. Blue-winged Warbler, pp356-357 in Cadman, M.D., Eagles, P.F.J., andF.M. Helleiner (eds.). Atlas of the BreedingBirds of Ontario. Federation of Ontario Natu-ralists and Long Point Bird Observatory. Uni-versity of Waterloo Press, Waterloo, Ontario.

Murray, B. J. and F. B. Gill. 1976. Behavioralinteractions of Blue-winged and Golden-winged Warblers. Wilson Bulletin 88:231–254.

Neville, K.J., R. Vallender and R.J. Robert-son. 2008. Nestling sex ratio of golden-wingedwarblers (Vermivora chrysoptera) in an intro-gressed population. Journal of Avian Biology39:599-604.

Parkes, K.C. 1951. The Genetics of the Gold-en-winged x Blue-Winged Warbler Complex.Wilson Bulletin 63:5-15.

Paquin, N. 2006. Demography and breedingsite fidelity in male Golden-winged Warblers(Vermivora chrysoptera). Honours Thesis,Department of Biology, Queen’s University,Kingston ON.

Queen’s University Biological Station(QUBS) Annual Report, 2004. pp.18. Avail-able at http://biology.queensu.ca/~qubs/qubs/Documents.html

Reed, L.P., R. Vallender and R.J. Robertson.2007. Provisioning rates by Golden-wingedWarblers. Wilson Journal of Ornithology119:350-355.

Rich, T. D., C. J. Beardmore, H. Berlanga, P. J. Blancher, M. S. W. Bradstreet, G. S. Butcher, D. W. Demarest, E. H. Dunn, W. C. Hunter, E. E. Iñigo-Elias, J. A. Ken -nedy, A. M. Martell, A. O. Panjabi, D. N.Pashley, K. V. Rosenberg, C. M. Rustay, J. S. Wendt and T. C. Will. 2004. Partners inFlight North American Landbird ConservationPlan. Cornell Lab of Ornithology, Ithaca, NewYork.

Roth, A.M. and S. Lutz. 2004. Relationshipbetween territorial male Golden-winged War-blers in managed aspen stands in northern Wisconsin, USA. Forest Science 50: 153-161.

Sauer, J.R., W. A. Link, J.D. Nichols and J.A. Royle. 2005. Using the North AmericanBreeding Bird Survey as a tool for conservation:A critique of BART et al. (2004). Journal ofWildlife Management 69:1321-1326.

Shapiro, L.H., R.A. Canterbury, D.M.Stover, and R.J. Flesicher. 2004. Reciprocalintrogression between Golden-winged Warblers(Vermivora chrysoptera) and Blue-winged War-blers (V. pinus) in eastern North America. Auk121: 1019-1030.

Smith, C.R., D.M. Pence, and R.J. O’Con-nor. 1993. Status of Neotropical migratorybirds in the northeast: A preliminary assess-ment. pp. 172-188 in Status and managementof Neotropical migratory birds (D. M. Finchand P. W. Stangel, Eds.). United States ForestService General Technical Report RM-229,Newton Corner, Massachusetts.

Spector, D.A. 1992. Wood-warbler song systems: A review of paruline singing behaviors. Current Ornithology 9:199-238.

Thompson, W.L. 2002. Towards reliable birdsurveys: Accounting for individuals present butnot detected. Auk 119:18-25.

Vallender, R. 2007a. Golden-winged Warbler,pp. 462-463 in Cadman, M.D., D.A. Suther-land, G.G. Beck, D. Lepage and A.R. Coutu-rier, eds. Atlas of the Breeding Birds ofOntario, 2001-2005. Bird Studies Canada,Environment Canada, Ontario Field Ornithol-ogists, Ontario Ministry of Natural Resourcesand Ontario Nature, Toronto.

Vallender, R. 2007b. Blue-winged Warbler, pp 460-461 in Cadman, M.D., D.A. Suther-land, G.G. Beck, D. Lepage and A.R. Coutu-rier, eds. Atlas of the Breeding Birds ofOntario, 2001-2005. Bird Studies Canada,Environment Canada, Ontario Field Ornithol-ogists, Ontario Ministry of Natural Resourcesand Ontario Nature, Toronto.

22


Vallender, R. and S. Leckie. 2007. Brewster’s Warbler/Lawrence’s Warbler, pp 464-465 inCadman, M.D., D.A. Sutherland, G.G. Beck,D. Lepage, and A.R. Couturier, eds. Atlas ofthe Breeding Birds of Ontario, 2001-2005.Bird Studies Canada, Environment Canada,Ontario Field Ornithologists, Ontario Min-istry of Natural Resources and Ontario Nature, Toronto.

Vallender R., V.L. Friesen and R.J. Robert-son. 2007a. Paternity and performance ofgolden-winged warblers (Vermivora chrysop tera)and golden-winged X blue-winged warbler (V.pinus) hybrids at the leading edge of a hybridzone. Behavioral Ecology and Socio biology61:1797-1807.

Vallender R., R.J. Robertson, V.L. Friesenand I. J. Lovette. 2007b. Complex hybridiza-tion dynamics between golden-winged andblue-winged warblers (Vermivora chrysopteraand Vermivora pinus) revealed by AFLP,microsatellite, intron and mtDNA markers.Molecular Ecology 16:2017-2029.

Weir R.D. 1989. Birds of the Kingston region.Quarry Press, Kingston, Ontario.

Laura E. King: Department of Biology, Queen’sUniversity, 116 Barrie Street, Kingston,Ontario, K7L 3N6, Canada

Virginia J. Emery: Department of Environmen-tal Science, Policy and Management, Universi-ty of California, Berkeley, CA, 94704, UnitedStates

Raleigh J. Robertson: Department of Biology,Queen’s University, 116 Barrie Street,Kingston, Ontario, K7L 3N6, Canada

Rachel Vallender: Cornell Laboratory ofOrnithology, 159 Sapsucker Woods Road,Ithaca, NY, 14850, United States

Paul R. Martin: Department of Biology,Queen’s University, 116 Barrie Street,Kingston, Ontario, K7L 3N6, Canada

For Correspondence, contact Paul R. Martin.Phone 613-533-6598; Fax: 613-533-6617; E-mail: [email protected]