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Rodent-Prey Content in Long-Term Samples ofBarn Owl (Tyto alba) Pellets from the NorthwesternUnited States Reflects Local Agricultural ChangeAuthor(s): R. Lee LymanSource: The American Midland Naturalist, 167(1):150-163. 2012.Published By: University of Notre DameDOI: http://dx.doi.org/10.1674/0003-0031-167.1.150URL: http://www.bioone.org/doi/full/10.1674/0003-0031-167.1.150

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Rodent-Prey Content in Long-Term Samples of Barn Owl (Tytoalba) Pellets from the Northwestern United States Reflects

Local Agricultural Change

R. LEE LYMAN1

Department of Anthropology, 107 Swallow Hall, University of Missouri, Columbia 65211

ABSTRACT.—Rodent prey contained in two temporally distinct collections of Barn Owl (Tytoalba) pellets from the same roost in southeastern Washington state (USA) differ in terms oftaxonomic abundances. Deer mice (Peromyscus maniculatus) dominate the fauna in the pelletsample deposited while much of the landscape was productive wheat field, and voles (Microtus

spp.) are a distant second. The fauna in the pellet sample deposited after 20% of thesurrounding landscape was placed in soil bank and converted to a grass non-producing fieldis dominated by voles with deer mice a close second. The coincident changes in localvegetation and in the rodent fauna are causally as well as temporally interrelated. Previouslocal studies have focused on the agricultural economics of coincident shifts in agriculturalpractices and rodent faunas. Results presented here indicate potential benefits to owl faunasof changes in agricultural practices and suggest that study of curated owl pellet faunascollected decades ago may reveal much about the long-term history of anthropogenicinfluences on rodent faunas.

INTRODUCTION

Agricultural practices in the United States have evolved remarkably over the past century.Productivity per hectare has, for example, increased tremendously as a result of artificialfertilization and genetic engineering of plant crops. As productivity has increased foodsurpluses have been generated; simultaneously, soil conservation has become a concern. Inthe northwestern United States an initial step toward soil conservation was to adopt ‘‘no-till’’cultivation in the late 1970s where the seed is planted directly through the residueremaining from the previous crop. Alternatively, the residue is burned prior to seeding(Papendick and Miller, 1977; Phillips et al., 1980). Burning was eventually abandonedbecause of air pollution. In the late 1990s, increasing amounts of previously productivefarmland were taken out of production and seeded to grass for a decade or more undercontract with the federal government. Such practice eliminates tillage and attendant loss oftopsoil from the erosive forces of wind and water, in effect banking top soil for future use,hence the term ‘‘soil bank.’’

Although no-till practices have beneficial effects with respect to soil conservation,reducing surpluses, and raising crop prices, the effects of shifts in land use practices onmammal communities are only now becoming understood. Early studies (e.g., Johnson,1987) suggested no-till practices had minimal impact on the density of voles, but laterstudies (e.g., Witmer et al., 2007) found that crop residue remaining in producing fieldssubject to no-till cultivation provided cover and insulation for many rodent taxa. Increasedcover plus the lack of disruption of burrow systems by cultivation resulted in higherpopulation densities of rodent pests and greater loss of new crops to these pests (Witmer etal., 2007). Fields in soil bank and with non-agricultural permanent grass cover may have thehighest densities of rodents (Capelli, 2005).

1 e-mail: lymanr@missouri.edu

Am. Midl. Nat. (2012) 167:150–163

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Most previous studies have focused on the influence of tillage practices on agriculturaleconomics and on shifts in the amount of crop destruction by rodent pests (Capelli, 2005;Witmer et al., 2007). Given ever-growing concerns over increased rates of biodiversity loss inparticular and conservation biology issues in general, the influence of shifts in tillagepractices over time on the taxonomic composition and abundances of rodent taxa hasreceived surprisingly little study. When it has received attention, it is largely from biologistswith access to natural history collections with detailed collection-history data (e.g., Rowe,2007; Moritz et al., 2008; Parra and Monahan, 2008; Tingley and Beissinger, 2009; Rowe etal., 2010). There is another source of long-term faunal data that has, as yet, seen little studywith respect to the influence of agricultural land use practices on local faunas: rodent preyfaunas in collections of owl pellets that span episodes of change in agricultural practices(Love et al., 2000).

Paleontologists have long assumed that changes in the taxonomic composition andtaxonomic abundances of small-mammal paleofaunas, especially rodents, reflect changes inhabitats, including when the paleofaunas were deposited in egested owl pellets (e.g.,Findley, 1964; Lundelius, 1964; Mellett, 1974; Mayhew, 1977; Redding, 1978). A growingamount of actualistic research generally referred to as fidelity studies confirms that thisassumption is often correct (e.g., Hadly, 1999; Lyman and Lyman, 2003; Terry, 2008, 2010a,b; Western and Behrensmeyer, 2009), though exceptions are always possible. In this paper, Idocument the influence of shifting agricultural land use practices on rodent faunas usingpaleontological techniques to compare rodent faunas extracted from temporally sequentcollections of owl pellets from one location.

MATERIALS AND METHODS

Mammalian faunas were reconstructed from temporally sequent collections of owl pelletsthat were obtained from the dirt floor of a shed used to house farm implements (trucks,combines, trailers) and located in southeastern Washington state (46u19.5919N,118u00.1829W). All pellets observed on the floor of the shed were collected during eachof four annual collection episodes (1999, 2000, 2001, 2009).

All collected owl pellets were placed in a plastic bag and transported to theZooarchaeology Laboratory at the University of Missouri–Columbia. Pellets were stored atroom temperature until processed. Each pellet was assigned a unique number, length anddiameter measured, disaggregated and its materials sorted with a dental pick and tweezers.All bones and teeth detected in each pellet were removed and placed in a uniquelynumbered plastic vial. To determine abundances of prey taxa, mandibles, skulls, andisolated maxillae were identified to the most specific level possible using comparativeskeletal collections of known taxonomy and published taxonomically diagnostic criteria(Ingles, 1965; Maser and Storm, 1970; Hall, 1981; Junge and Hoffmann, 1981; Verts andCarraway, 1998). Taxonomic abundances were tallied as the minimum number ofindividuals necessary to account for all identified remains in each annual collection ofowl pellets (Grayson, 1984; Lyman, 2008).

A single large owl was observed leaving the shed in summer 1999. Size and shape ofindividual pellets—5–6 cm long, 2.5–3 cm diameter, oval—were similar across all samples ofpellets, and suggest the taxonomic identify of the owl predator is the barn owl (Tyto alba)(Wilson, 1938; Moon, 1940). Barn owls are opportunistic feeders (Smith et al., 1972; Marti,1988; Marra et al., 1989), suggesting mammalian prey in the pellet samples likely reflect thesmall mammal fauna on the landscape (Hadly, 1999; Terry, 2010a). The typical foragingradius or home range of barn owls is within 5–6 km of a roost or nest (Cottam and Nelson,

2012 LYMAN: BARN OWL RODENT PREY REFLECT AGRICULTURAL LANDSCAPES 151

1937; Cunningham, 1960; Smith et al., 1974; Taylor, 1994). Mammalian prey in the pelletcollections studied here were probably taken within such a foraging radius; none of therepresented prey species is biogeographically unexpected (Dalquest, 1948; Johnson andCassidy, 1997).

The condition of mammal bones in the pellets—relatively complete skeletons, most longbones anatomically complete and not fragmented—was consistent across all pelletcollections and also implicates the barn owl (Dodson and Wexlar, 1979; Hoffman, 1988;Andrews, 1990; Kusmer, 1990). While it is unlikely that the same individual owl deposited allpellets collected given the temporal differences between the first and last pellet sample(10 y) (the average life expectancy of a barn owl in the wild is #2 y (www.raptorcenter.org;accessed 6 Dec. 2010), there is no evidence to suggest a change in owl taxon during theinterval of pellet accumulation. Therefore any variation in composition and abundance ofprey species is unlikely to be the result of variation in predator species. Furthermore,because all owl pellets described here originated from the same roost, any variation in preycontent across different pellet collections cannot be attributed to variation in the spatiallocation of the roost or to variation in vegetation (and fauna) associated with differentroosts. Given no evidence for change in predator taxon, I assume, as in paleontologicalfidelity studies (e.g., Terry, 2010b), that changes in taxonomic abundances reflect changesin environment (broadly conceived), particularly vegetation.

The equipment shed is a corrugated-tin shell enclosed on three sides and the top, with afront opening approximately 15 m wide and 5 m high. It sits on an artificially leveled area inthe bottom of a shallow, steep-sided, south-draining canyon. Vegetation in the canyonincludes a dense stand of ca. 2 m tall grass (Agropyron spp., Bromus spp., Poa sp.) with a fewscattered trees (Pinus sp.), shrubs (Rosa sp.) and forbs; most of the canyon slopes were in useas horse pasture from the 1970s through 2010 (pers. obs.). All ridges defining the canyonedges were wheat fields that were in production from the 1970s through the 1990s (R. J.Lyman, 2001 pers. comm.). For purposes of soil conservation, in the fall of 2000 thenorthwest-ridge field, approximately 20% of the land area (25 ha) in the immediateenvironment of the shed was placed in soil bank and remaining wheat stubble was seeded tograss (bluebunch wheatgrass (Pseudoregneria spicata), slender wheatgrass (Agropyrontrachycaulum), big bluegrass (Poa ampla), and Indian ricegrass (Oryzopis hymenoides)). ByJul. 2001 this field had a patchy stand of grass; areas of partially deteriorated field residuewithout green vegetation cover existed on ,30% of the field. By 2006, most of the fieldresidue had deteriorated or been removed by wind and a relatively continuous grass coverexisted over ,95% of the field (pers. obs.).

Finally, to evaluate climatic changes that have occurred at this site over the temporalperiod under consideration, maximum annual temperature, minimum annual temperature,and annual precipitation data were collected for the years 1998–2009 (inclusive) from theweb site for PRISM Climate Group (http://www.prism.oregonstate.edu; accessed 6 Dec.2010) for the latitude–longitude coordinates of the equipment shed.

RESULTS

The taxonomic composition and abundances of prey species in each of the temporallydistinct owl pellet collections are summarized in Table 1. Local vegetation changed betweenthe fall of 2000 and spring of 2001 (between pellet collection episodes) as a result ofartificial seeding of the northwest ridge to grass and discontinuation of use of that ridge foragricultural purposes. For purposes of this analysis, the 1999 and 2000 samples of owl pelletswere lumped together to represent an agricultural prey fauna, and the 2001 and 2009

152 THE AMERICAN MIDLAND NATURALIST 167(1)

samples were lumped together to represent a non-agricultural prey fauna (Lyman andLyman, 2003).

The agricultural prey fauna is dominated by deer mice (Peromyscus maniculatus), whichoutnumber voles (Microtus spp.) 3.4:1. In contrast, that ratio in the non-agricultural preyfauna is 1:2.1. Deer mice dominate the agricultural prey fauna whereas voles dominate thenon-agricultural fauna (Fig. 1). Other prey taxa are so rare as to be present or absent largelyas a result of sampling error, although western harvest mice (Reithrodontomys megalotis) mayappear in the non-agricultural fauna as a function of their occurrence in the patchy grassnon-productive field where they would be more easily captured than if in the tall dense grassof the horse pasture.

Prey richness increased from five species for the agricultural sample to six species for thenon-agricultural sample. Prey heterogeneity also increased; using the abundances of genera,the reciprocal of Simpson’s index (Magurran, 2004) is 1.725 in the agricultural fauna and is2.285 in the non-agricultural fauna. Chi square analysis indicates the two faunas aresignificantly different (chi2 5 96.63, P , 0.0001). Analysis of adjusted residuals [read asstandard normal deviates (Everitt, 1977)] indicates that abundances of Sorex and Sylvilagusare not the source of the difference, and Thomomys is contributing a minor amount to thedifference (Table 2). There are significantly more Peromyscus in the agricultural sample (andfewer in the non-agricultural sample) than expected, and significantly fewer Reithrodontomysand Microtus in the agricultural sample (and more in the non-agricultural sample) thanexpected.

Analysis of climate data reveals no correlation between year and annual precipitation(Pearson’s r 5 0.08, P . 0.8), but both maximum (r 5 20.747, P 5 0.005) and minimum(r 5 20.711, P 5 0.009) annual temperatures are inversely correlated with year. Year-to-yearfluctuation in temperature has been minimal; maximum temperature dropped about 5 Fand minimum temperature dropped about 4 F in the 12 y included in the analysis (1998–2009). There is no significant correlation between any of the three climatic variables andrelative abundances of either deer mice or voles (r , 0.3, P . 0.7 in all).

DISCUSSION

The conversion of a significant area of no-till agricultural land to non-agriculturalgrassland in Autumn 2000 is the most likely cause for the change in abundances of owl prey.Change in agricultural practices for approximately 20% of the landscape immediatelysurrounding the equipment shed (within ,5 km) likely created differences in the

TABLE 1.—Minimum number of individuals (MNI) from four annual collections of owl pellets

Taxonomic name Common name 1999 2000 2001 2009

Sorex vagrans Vagrant shrew 4 1 3Sylvilagus cf. nuttallii Nuttall’s cottontail 1Reithrodontomys megalotis Western harvest mouse 5 10Peromyscus maniculatus Deer mouse 174 10 10 30Microtus sp. Vole 5 8 9Microtus longicaudus Long-tailed vole 6 4Microtus montanus Montane vole 43 11 38 23Thomomys talpoides Northern pocket gopher 6 1g MNI 5 233 21 69 79N of pellets 60 6 22 20

2012 LYMAN: BARN OWL RODENT PREY REFLECT AGRICULTURAL LANDSCAPES 153

FIG. 1.—Relative abundances of mammalian genera in agricultural (1999, 2000) and non-agricultural(2001, 2009) owl pellet collections (data from Table 1)

TABLE 2.—Expected (Exp) abundances and adjusted residuals (Adj Resid) from chi2 analysiscomparing the agricultural and non-agricultural faunas

Taxon Ag exp Adj resid P Non-Ag exp Adj resid P

Sorex 5.05 20.777 .0.1 2.95 0.776 .0.1Sylvilagus 0.63 0.588 .0.07 0.37 20.766 .0.07Reithrodontomys 9.48 25.272 ,0.001 5.50 5.194 ,0.001Peromyscus 141.53 17.246 ,0.001 82.46 28.839 ,0.001Microtus 92.88 28.924 ,0.001 54.12 7.275 ,0.001Thomomys 4.42 1.258 ,0.02 2.58 21.249 ,0.02

154 THE AMERICAN MIDLAND NATURALIST 167(1)

abundances of particular rodent taxa available to the owl predator. Three pellets in the 1999sample of pellets contained wheat kernals; no pellets in later samples contained wheatkernels (Lyman and Lyman, 2003). Deer mice, being granivores, likely spent much time inharvested wheat fields foraging for waste grain and these fields were the source of wheatkernals in the pellets. The lack of tall cover in the stubble field would have made deer micesusceptible to aerial predation. Barn owls can locate prey based on sound in total darkness(Payne and Drury, 1958; Konishi, 1973), but their success increases with minimal light andgreater visibility (Dice, 1945; Payne, 1962). The horse pasture adjacent to the wheat fieldswould have been much less easily hunted because visibility would be impaired and access toprey hindered by the thick tall grass. It is likely that during the pre-2001 agricultural phasethe owls spent much foraging time flying over the wheat-stubble fields bordering the canyoncontaining the equipment shed.

Voles prefer grassland habitats and tend to displace deer mice (Feldhamer, 1979;Randall and Johnson, 1979). The first several years after 2000, the field taken out ofproduction and seeded to grass did not have uniformly thick and dense grass cover butrather an estimated 70% of the formerly producing wheat field was covered with grass.Voles would have been more numerous in that field than in previous years in early 2001because of no tillage (Negus et al., 1977; Capelli, 2005) and also more susceptible to aerialpredation because of less protective cover. Foraging flights over that patchy grass fieldwould have produced more voles than deer mice; barn owls have greater foraging successwhen vegetation is patchy and open (Wooster, 1936; Kirkpatrick and Conway, 1947; Fastand Ambrose, 1976; Dickman et al., 1991). The shift in abundances of deer mice relative tovoles coincides temporally with the shift in local vegetation and implies a casual linkbetween the two. More grass and less tillage has been shown in nearby areas to result inmore voles and fewer deer mice (Capelli, 2005; Witmer et al., 2007). Assuming no changein the opportunistic foraging behavior of the owls as a function of field conversion, thegreater availability of voles in the new patchy grass non-agricultural field would haveresulted in the observed shift in prey ratios.

Other explanations for the shift in community structure and relative abundances of volesand deer mice are less likely. First, the shift is unlikely to reflect a change in local climate.Year to year fluctuation in temperature has been minimal, and there is no correlationbetween small mammal abundance and climate variables. The second possibility is thatsome vole populations in eastern Washington cycle in numbers, peaking every 3 y (Randalland Johnson, 1979). Perhaps voles were less abundant on the landscape during theagricultural period represented by the pellets but were at peak abundance during the non-agricultural period, and thus were more available to predators as a result of a ‘‘natural’’cycle in abundance unrelated to the landscape. If this were the case, the demography of thevole samples may display a larger abundance of young as the population increases (Craigand Oertel, 1966). Comparison of the frequency distributions of maximum lengths of allvole femora and all vole humeri in the agricultural sample with those for the non-agricultural sample indicates there is no significant difference in vole demography betweenthe two samples [Fig. 2; Kolmogorov-Smirnov two sample D 5 0.167 for humeri, D 5 0.071for femora, P . 0.05 for both (Klein and Cruz-Uribe, 1984)].

A third possibility is that differences in the seasonality of prey acquisition has createddifferences in taxonomic abundances. Size classes of femora and humeri suggest that theagricultural prey fauna and the non-agricultural prey fauna do not differ in the ontogeny ofeither voles or deer mice (Figs. 2 and 3). Both samples have equivalent age-frequencystructures of deer mice and of voles based on lengths of femora and humeri (Kolmogorov-

2012 LYMAN: BARN OWL RODENT PREY REFLECT AGRICULTURAL LANDSCAPES 155

Smirnov two-sample D 5 0.118 for humeri, D 5 0.146 for femora, P . 0.05 for both). Thus,there is no evidence for difference in the season of prey acquisition.

A fourth possibility concerns differences in behavioral patterns of the two major preyspecies. Deer mice are nocturnal granivores and the represented vole species are herbivoresthat are active during both day and night hours. If the owls varied the timing of their

FIG. 2.—Abundances of size classes of Microtus spp. femur lengths and humerus lengths in theagricultural and non-agricultural collections

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FIG. 3.—Abundances of size classes of Peromyscus maniculatus femur lengths and humerus lengths inthe agricultural and non-agricultural collections

2012 LYMAN: BARN OWL RODENT PREY REFLECT AGRICULTURAL LANDSCAPES 157

foraging flights coincident with the change from agricultural fields to non-agriculturallandscapes, that could account for the shift in the ratio of deer mice to voles. Because theowls were not observed on foraging flights, I cannot directly evaluate this possibility.However, North American barn owls forage mostly nocturnally (Taylor, 1994) and onlyoccasionally forage diurnally (Harte, 1954). A shift in the timing of foraging flightscoincident with change in the agricultural landscape is, therefore, unlikely to be the causeof differences in prey. Another possibility is that a change in local mammal predatorsresulted in depletion of deer mice to the benefit of voles; no data are available to evaluatethis possibility.

Finally, the change in relative abundances of deer mice and voles is not likely a functionof sample size. The agricultural sample includes 66 pellets and a total of 254 prey; the non-agricultural sample includes 42 pellets and 148 total prey. In light of the species-arearelationship (e.g., Lomolino, 2000), those differences in sample size suggest that theagricultural sample should be taxonomically richer and more heterogeneous than the non-agricultural sample simply because the latter is a smaller sample. However, the agriculturalsample includes remains of five species and the reciprocal of Simpson’s index is 1.725, andthe non-agricultural sample includes remains of six species and the reciprocal of Simpson’sindex is 2.285. Both taxonomic richness and taxonomic heterogeneity values suggest thatdifferences in sample size—measured as either the number of pellets contributing prey orthe total MNI of prey per sample—is not likely to be causing the difference in relativeabundances of deer mice and voles. Typically the relationship between sample size and bothtaxonomic richness and heterogeneity in paleozoological collections is positive (Grayson,1984; Lyman, 2008).

The next question concerns the implications of shifts in prey for the long-termpersistence of local owls in this habitat. Did change in the taxonomic composition of thediet create a shift in food intake amount? The average number of individual prey per pelletin the agricultural sample was 4.38 6 1.88 and 3.61 6 1.71 in the non-agricultural sample.The two averages are significantly different (Student’s t 5 2.13, P 5 0.036 two-tailed test),indicating the non-agricultural pellets contained, on average, significantly fewer preyanimals than the agricultural sample. This reduction in number is likely offset by a changein the average weight of prey items. The average weight of adult deer mice in the study areais about 21 g, and the average weight of adult voles is 45 g (Verts and Carraway, 1998). Mostdeer mice in the owl pellet samples were skeletally immature (unfused long-bone epiphyses)and not of full adult body size (Fig. 3); many of the voles were also young but were close toadult body size (Fig. 2). Further, only 16% of deer mice femora and humeri had bothproximal and distal epiphyses fused whereas more than 31% of vole femora and humeri hadboth proximal and distal epiphyses fused (e.g., Lyman et al., 2001). That is, mostly juveniledeer mice were captured but more adult voles were captured. Together, these observationsindicate that the difference in average number of prey per pellet in the two samples is likelythe result of smaller prey (juvenile deer mice) being ingested during the agricultural phaseand of larger prey (more adult-size voles) being ingested during the non-agricultural phase.Thus, the amount of food intake likely did not change coincident with the change invegetation.

I have not calculated the prey biomass represented (e.g., Hamilton, 1980; Steenhof, 1983;Marti, 2009) for two reasons. First, the values used to convert prey frequency to biomassassume each individual prey animal was of adult body size (e.g., Steenhof, 1983). Previousresearch shows that long-bone length in deer mice increases with individual age until adultsize is attained (Svihla, 1934; McIntosh, 1955; King and Eleftheriou, 1960; Layne, 1968);

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there is a strong positive allometric relationship between humerus length and body weightand between femur length and body weight. However, humeri and femora are not asabundant in the owl pellet collections as are skulls and mandibles, so any calculation oftaxon specific biomass for an annual pellet collection would be an underestimate ofunknowable magnitude.

The second reason to not calculate prey biomass concerns how prey frequencies aredetermined. The number of prey in Table 1 is based on the total of the most commonskeletal element (left mandible, skull, etc.) in an annual collection of pellets. The number isa minimum number because it is assumed that a left mandible or maxilla of, say, Peromyscusmaniculatus, in one pellet may have its bilateral mate in another pellet, a possibility that hasbeen documented in the 1999 collection (Lyman et al., 2003). If each pellet is considered tobe independent of every other pellet, the frequency of deer mice increases from 184 for the1999–2000 collections to 198, and voles increase from 59 to 62. It is for this reason thatpaleontological data on taxonomic abundances is not interval scale and often not evenordinal scale (Lyman, 2008). To convert the taxonomic abundance data in Table 1 tobiomass would produce a false sense of accuracy. Similarly, rarefaction might be used toreduce the size of the agricultural sample to that of the non-agricultural sample, but thisraises the question of which set of MNI values to use—those derived from each annual pelletcollection as a whole, or MNI values determined for each individual pellet and summed foreach annual collection? There is no unequivocal answer to this question (Grayson, 1984;Lyman, 2008).

Three things are clear without calculation of biomass or rarefaction analysis. First, there isa shift in the abundance of deer mice relative to the abundance of voles; second, there arefewer prey per pellet in the non-agricultural sample than in the agricultural sample; andthird, the percent abundance of skeletally mature voles is greater than the percentabundance of skeletally mature deer mice. In combination, these three observations arereadily accounted for by a shift in owl dietary intake.

The implications of shifts in prey for the long-term survival of local owls are unclear.However, one thing is suggested. Assuming that prey animals were captured one at a time,fewer prey animals per pellet suggests less foraging time was spent subsequent to the changein the agricultural landscape. If increased prey handling costs did not offset decreased timedevoted to foraging flights resulting from an increase in prey size (small deer mice to largevoles), foraging would be more energy efficient (less search time because there are fewerprey capture events per flight) (Stephens and Krebs, 1986) as well as lowered susceptibilityof the owls to predation. Both factors would enhance the long-term survival of the local owlpopulation.

CONCLUSION

Many variables must be considered as agricultural practices evolve in response toperceived needs in economics, conservation, and human nutrition. One that has receivedminimal attention is the biodiversity and composition of rodent faunas associated withagriculture. Love et al. (2000) showed that the mammalian prey contained in barn owlpellets provided insight to how rodent taxa responded to changes in agricultural practices inEngland. I am unaware of similar studies in the United States. Some paleontological fidelitystudies (e.g., Terry, 2010a) are in several ways similar to Love et al.’s (2000) seminal work.Both use the modern faunal remains in owl pellets as in some way accurate reflections ofenvironments that produced the fauna.

2012 LYMAN: BARN OWL RODENT PREY REFLECT AGRICULTURAL LANDSCAPES 159

In the study described here the method of paleontological fidelity studies was wed withthe known history of a small portion of the agricultural landscape in southeasternWashington state, similar to Love et al.’s (2000) study. The two samples of mammalian prey,deposited prior to and subsequent to conversion of a portion of landscape near the owlroost from a producing wheat field to a soil conservation field seeded permanently to grass,indicate the taxonomic composition of the rodent fauna remained relatively stable butabundances of frequently represented taxa shifted markedly. Granivorous deer mice weremost abundant during the first phase, but herbivorous voles became dominate during thesecond phase. The temporal coincidence of the agricultural conversion and the shift inrelative abundances of prey taxa represents a cause–effect relationship; there is no evidenceto support any other possible explanation for the shift in prey abundances.

Monitoring raptor, particularly owl, diets via pellet analysis has taken place for manydecades (e.g., Errington, 1930). It is a relatively inexpensive technique for undertakingfidelity studies and for monitoring the influences of changes in agricultural practices onrodent faunas. Synergy of the two produces insights of benefit to conservation biology inaddition to agricultural economics. If owl pellet faunas collected decades ago (e.g., Fielder,1982; Knight and Jackman, 1984) still exist, they have the potential to provide significantinformation on the temporally deep history of the influences of agricultural practices onlocal faunas. Further, owl pellet faunas may also reveal other influences of industrial-agehuman societies if it can be argued that the owls that produced the pellets did not forageover agricultural lands. As we settle into the third millennium, such information will likelyincrease in value as the human population continues to grow and to influence globalclimates and local habitats.

Acknowledgments.—I appreciate the comments of two anonymous reviewers, especially the one whocleaned up the structure. Thanks to my late brother, R. Jay Lyman, and his wife Karen, for access to theirequipment shed over the years. I dedicate this paper to Jay; I miss those Aug. days in the wheat fields.

LITERATURE CITED

ANDREWS, P. 1990. Owls, Caves and Fossils. University of Chicago Press, Chicago. 231 p.CAPELLI, J. L. 2005. Landscape Ecology of Rodents in a No-Till Agriculture System. Master of Science

Thesis, Washington State University, Pullman.COTTAM, C. AND A. L. NELSON. 1937. Winter nesting and winter food of the barn owl in South Carolina.

Wilson Bull., 49:283–285.CRAIG, G. Y. AND G. OERTEL. 1966. Deterministic models of living and fossil populations of animal. Quart.

J. Geol. Soc. London, 122:315–355.CUNNINGHAM, J. D. 1960. Food habits of the horned and barn owls. Condor, 62:222.DALQUEST, W. W. 1948. Mammals of Washington. University of Kansas Museum of Natural History

Publication 2. 444 p.DICE, L. R. 1945. Minimum intensities of illumination under which owls can find dead prey by sight.

Amer. Nat., 79:385–416.DICKMAN, C. R., M. PREDAVEC AND A. J. LYNAM. 1991. Differential predation of size and sex classes of mice

by the barn owl, Tyto alba. Oikos, 62:67–76.DODSON, P. AND D. WEXLAR. 1979. Taphonomic investigations of owl pellets. Paleobiology, 5:275–284.ERRINGTON, P. L. 1930. The pellet analysis method of raptor food habits study. Condor, 32:292–296.EVERITT, B. S. 1977. The Analysis of Contingency Tables. Chapman and Hall, London.FAST, S. J. AND H. W. AMBROSE, III. 1976. Prey preference and hunting habitat selection in the barn owl.

Am. Midl. Nat., 96:503–507.FELDHAMER, G. A. 1979. Vegetative and edaphic factors affecting abundance and distribution of small

mammals in southeast Oregon. Great Basin Nat., 39:207–218.FIELDER, P. C. 1982. Barn owl food habits along the mid-Columbia River, Washington. Murrelet, 63:29–30.

160 THE AMERICAN MIDLAND NATURALIST 167(1)

FINDLEY, J. S. 1964. Paleoecological reconstruction: vertebrate limitations, p. 23–25. In: J. J. Hester and J.Schoenwetter (eds.). The Reconstruction of Past Environments. Fort Burgwin Research CenterPublication 3. Taos, New Mexico.

GRAYSON, D. K. 1984. Quantitative Zooarchaeology. Academic Press, Orlando, Florida. 202 p.HADLY, E. A. 1999. Fidelity of terrestrial vertebrate fossils to a modern ecosystem. Palaeogeog., Palaeoclim.,

Palaeoecol., 149:389–409.HALL, E. R. 1981. The Mammals of North America, 2nd ed. Wiley, New York. 1175 p.HAMILTON, K. L. 1980. A technique for estimating barn owl prey biomass. Raptor Res., 14:52–55.HARTE, K. 1954. Barn owl hunting by daylight. Wilson Bull., 66:270.HOFFMAN, R. 1988. The contribution of raptorial birds to patterning in small mammal assemblages.

Paleobiology, 14:81–90.INGLES, L. G. 1965. Mammals of the Pacific States: California, Oregon, Washington. Stanford University

Press, Stanford, California. 506 p.JOHNSON, D. R. 1987. Effect of alternative tillage systems on rodent density in the Palouse region.

Northwest Sci., 61:37–40.JOHNSON, R. E. AND K. M. CASSIDY. 1997. Terrestrial mammals of Washington state: location data and

predicted distributions. Washington State Gap Analysis—Final Report, Vol. 3. WashingtonCooperative Fish and Wildlife Unit, University of Washington, Seattle. 304 p.

JUNGE, J. A. AND R. S. HOFFMANN. 1981. An annotated key to the long-tailed shrews (genus Sorex) of theUnited States and Canada, with notes on Middle American Sorex. Univ. Kansas Mus. Nat. Hist.Occ. Pap., 94:1–48.

KING, J. A. AND B. E. ELEFTHERIOU. 1960. Differential growth in the skulls of two subspecies of deermice.Growth, 24:179–192.

KIRKPATRICK, C. M. AND C. H. CONWAY. 1947. The winter foods of some Indiana owls. Am. Midl. Nat.,38:755–766.

KLEIN, R. G. AND K. CRUZ-URIBE. 1984. The Analysis of Animal Bones from Archeological Sites. Universityof Chicago Press, Chicago.

KNIGHT, R. L. AND R. E. JACKMAN. 1984. Food-niche relationships between great horned owls and commonbarn-owls in eastern Washington. Auk, 101:175–179.

KONISHI, M. 1973. How the owl tracks its prey. Am. Sci., 61:414–424.KUSMER, K. D. 1990. Taphonomy of owl pellet digestion. J. Paleontol., 64:629–637.LAYNE, J. N. 1968. Ontogeny, p. 148–253. In: J. A. King (ed.). Biology of Peromyscus (Rodentia). American

Society of Mammalogists, Special Publication 2.LOMOLINO, M. V. 2000. Ecology’s most general, yet protean pattern: the species-area relationship. J.

Biogeog., 27:17–26.LOVE, R. A., C. WEBBON, D. E. GLUE AND S. HARRIS. 2000. Changes in the food of British barn owls (Tyto

alba) between 1974 and 1997. Mam. Rev., 30:107–129.LUNDELIUS, E. JR. 1964. The use of vertebrates in paleoecological reconstructions, p. 26–31. In: J. J.

Hester and J. Schoenwetter (eds.). The Reconstruction of Past Environments. Fort BurgwinResearch Center Publication 3. Taos, New Mexico.

LYMAN, R. L. 2008. Quantitative Paleozoology. Cambridge University Press, Cambridge. 348 p.——— AND R. J. LYMAN. 2003. Lessons from temporal variation in the mammalian faunas from two

collections of owl pellets in Columbia County, Washington. Internat. J. Osteoarchaeol.,13:150–156.

———, E. POWER AND R. J. LYMAN. 2001. Ontogeny of deer mice (Peromyscus maniculatus) and montanevoles (Microtus montanus) as owl prey. Am. Midl. Nat., 146:72–79.

———, ——— AND R. J. LYMAN. 2003. Quantification and sampling of faunal remains in owl pellets. J.Taphonomy, 1:3–14.

MAGURRAN, A. E. 2004. Measuring Biological Diversity. Blackwell Publishing, Malden, Massachusetts.MARRA, P. P., B. M. BURKE AND I. ALBERGAMO. 1989. An analysis of common barn-owl pellets from

Louisiana. Southwest. Nat., 34:142–144.MARTI, C. D. 1988. A long-term study of food-niche dynamics in the common barn-owl: comparisons

within and between populations. Canad. J. Zool., 66:1803–1812.

2012 LYMAN: BARN OWL RODENT PREY REFLECT AGRICULTURAL LANDSCAPES 161

———. 2009. A comparison of methods for estimating prey biomass of barn owls. J. Raptor Res.,43:61–63.

MASER, C. AND R. M. STORM. 1970. A Key to Microtinae of the Pacific Northwest. Oregon State UniversityBookstore, Corvallis. 162 p.

MAYHEW, D. F. 1977. Avian predators as accumulators of fossil mammal material. Boreas, 6:25–31.MCINTOSH, W. B. 1955. The applicability of covariance analysis for comparison of body and skeletal

measurements between two races of the deermouse, Peromyscus maniculatus. Contributions fromthe Laboratory of Vertebrate Biology 72. University of Michigan, Ann Arbor.

MELLETT, J. S. 1974. Scatological origin of microvertebrate fossil accumulations. Science, 185:349–350.MOON, E. L. 1940. Notes on hawk and owl pellet formation and identification. Trans. Kansas Acad. Sci.,

43:457–466.MORITZ, C., J. L. PATTON, C. J. CONROY, J. L. PARRA, G. C. WHITE AND S. R. BEISSINGER. 2008. Impact of a

century of climate change on small-mammal communities in Yosemite National Park, USA.Science, 322:261–264.

NEGUS, N., P. BERGER AND L. FORSLUND. 1977. Reproductive strategy in Microtus montanus. J. Mamm.,58:347–353.

PAPENDICK, R. I. AND D. E. MILLER. 1977. Conservation tillage in the Pacific Northwest. J. Soil and WaterCons., 32:49–56.

PARRA, J. L. AND W. R. MONAHAN. 2008. Variability in 20th century climate change reconstructions and itsconsequences for predicting geographic responses of California mammals. Glob. Change Biol.,14:2215–2231.

PAYNE, R. S. 1962. How the barn owl locates prey by hearing. Living Bird, 1:151–159.——— AND W. H. DRURY Jr. 1958. Marksman of the darkness. Nat. Hist., 67:316–323.PHILLIPS, R. E., R. L. BLEVINSL, G. W. THOMAS, W. W. FRYE AND S. H. PHILLIPS. 1980. No-tillage agriculture.

Science, 208:1108–1113.RANDALL, J. A. AND R. E. JOHNSON. 1979. Population densities and habitat occupancy by Microtus

longicaudus and M. montanus. J. Mamm., 60:217–219.REDDING, R. W. 1978. Rodents and the archaeological paleoenvironment: considerations, problems, and

the future, p. 63–68. In: R. H. Meadow and M. A. Zeder (eds.). Approaches to Faunal Analysisin the Middle East. Peabody Museum Bulletin 2, Cambridge, Massachusetts.

ROWE, R. J. 2007. Legacies of land use and recent climatic change: the small mammal fauna in themountains of Utah. Am. Nat., 170:242–257.

———, J. A. FINARELLI AND E. A. RICKART. 2010. Range dynamics of small mammals along an elevationalgradient over an 80-year interval. Glob. Change Biol., 16:2930–2943.

SMITH, D. G., C. F. WILSON AND H. H. FROST. 1972. Seasonal food habits of barn owls in Utah. Great BasinNat., 32:229–234.

———, ——— AND H. H. FROST. 1974. History and ecology of a colony of barn owls in Utah. Condor,76:131–136.

STEENHOF, K. 1983. Prey weights for computing percent biomass in raptor diets. Raptor Res., 17:15–27.STEPHENS, D. W. AND J. R. KREBS. 1986. Foraging Theory. Princeton University Press, Princeton, New

Jersey. 247 p.SVIHLA, A. 1934. Development and growth of deermice (Peromyscus maniculatus artemisiae). J. Mamm.,

15:99–104.TAYLOR, I. 1994. Barn Owls: Predator–Prey Relationships and Conservation. Cambridge University Press,

Cambridge, UK. 304 p.TERRY, R. C. 2008. Modeling the effects of predation, prey cycling, and time averaging on relative

abundance in raptor-generated small mammal death assemblages. Palaios, 23:402–410.———. 2010a. On raptors and rodents: testing the ecological fidelity and spatiotemporal resolution of

cave death assemblages. Paleobiology, 36:137–160.———. 2010b. The dead do not lie: using skeletal remains for rapid assessment of historical small-

mammal community baselines. Proc. Royal Soc. B, 277:1193–1201.TINGLEY, M. W. AND S. W. BEISSINGER. 2009. Detecting range shifts from historical species occurrences:

new perspectives on old data. TREE, 24:625–633.

162 THE AMERICAN MIDLAND NATURALIST 167(1)

VERTS, B. J. AND L. N. CARRAWAY. 1998. Land Mammals of Oregon. University of California Press, Berkeley.668 p.

WESTERN, D. AND A. K. BEHRENSMEYER. 2009. Bone assemblages track animal community structure over40 years in an African savanna ecosystem. Science, 324:1061–1064.

WILSON, K. A. 1938. Owl studies at Ann Arbor, Michigan. Auk, 55:187–197.WITMER, G., R. SAYLER, D. HUGGINS AND J. CAPELLI. 2007. Ecology and management of rodents in no-till

agriculture in Washington, USA. Integrative Biol., 2:154–164.WOOSTER, L. D. 1936. The contents of owl pellets as indicators of habitat preferences of small mammals.

Trans. Kansas Acad. Sci., 39:395–397.

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2012 LYMAN: BARN OWL RODENT PREY REFLECT AGRICULTURAL LANDSCAPES 163