02542nas a2200289 4500008004100000245011500041210006900156300001300225490000800238520164800246653002401894653001701918653002101935653003101956653001501987653001302002653001902015653002402034653002502058653002002083653001702103100001702120700001702137700001902154700002002173856005902193 2010 eng d00aCommunity-level patterns of host use by the Brown-headed Cowbird (Molothrus ater), a generalist brood parasite0 aCommunitylevel patterns of host use by the Brownheaded Cowbird M a263 -2730 v1273 a

Quantifying community-level host use by generalist brood parasites is important because it provides a measure of the resources that parasites need for reproduction. During the 2002–2007 breeding seasons, we quantified host use by the Brown-headed Cowbird (Molothrus ater) at Konza Prairie Biological Station in northeast Kansas. Overall, 54.4% of nests (n = 2,621) of 22 passerine host species that typically accept parasitic eggs were parasitized, and parasitized nests contained an average of 1.9 ± 1.03 (SD) Brown-headed Cowbird eggs, nestlings, or both. Multiple parasitism was common on the study site in all years: 55.7% of parasitized nests (n = 1,425) received ≥2 Brown-headed Cowbird eggs. The Bell's Vireo (Vireo bellii; 70.5%) and the Dickcissel (Spiza americana; 69.6%) were parasitized at a significantly greater rate than the Red-winged Blackbird (Agelaius phoeniceus, 21.9%); collectively, these three species represented 85.8% of potential host nests found in all years. The host preference of Brown-headed Cowbirds did not appear to shift among the three species and instead they exhibited a consistent preference for Dickcissel nests over the course of the breeding season and among years. Both the rate and the intensity of parasitism on Dickcissels were significantly lower during the present study than in one conducted several decades earlier at the same site. Our results indicate that cowbirds in northeast Kansas differentially parasitize hosts, that most cowbird eggs are laid in the nests of a small number of host species, and that the Dickcissel appears to be preferred over other hosts.

10aAgelaius phoeniceus10aBell's Vireo10abrood parasitism10acommunity-level parasitism10aDickcissel10ahost use10aMolothrus ater10amultiple parasitism10ared-winged blackbird10aSpiza americana10aVireo bellii1 aRivers, J.W.1 aJensen, W.E.1 aKosciuch, K.L.1 aRothstein, S.I. uhttps://academic.oup.com/auk/article/127/2/263/514838202329nas a2200133 4500008004100000245009800041210006900139300001300208490000700221520185300228100001902081700002102100856007402121 2008 eng d00aCowbird removals unexpectedly increase productivity of a brood parasite and the songbird host0 aCowbird removals unexpectedly increase productivity of a brood p a537 -5480 v183 a

Generalist brood parasites reduce productivity and population growth of avian hosts and have been implicated in population declines of several songbirds of conservation concern. To estimate the demographic effects of brood parasitism on Bell's Vireos (Vireo bellii), we removed Brown-headed Cowbirds (Molothrus ater) in a replicated switchback experimental design. Cowbird removals decreased parasitism frequency from 77% and 85% at unmanipulated plots to 58% and 47% at removal plots in 2004 and 2005, respectively. Vireo productivity per pair was higher at cowbird removal plots when years were pooled (mean = 2.6 ± 0.2 [SE] young per pair) compared to unmanipulated plots (1.2 ± 0.1). Nest desertion frequency was lower at cowbird removal plots (35% of parasitized nests) compared to unmanipulated plots (69%) because removal of host eggs was the proximate cue for nest desertion, and vireos experienced lower rates of egg loss at cowbird removal plots. Nest success was higher among unparasitized than parasitized nests, and parasitized nests at cowbird removal plots had a higher probability of success than parasitized nests at unmanipulated plots. Unexpectedly, cowbird productivity from vireo pairs was higher at cowbird removal plots (mean = 0.3 ± 0.06 young per pair) than at unmanipulated plots (0.1 ± 0.03) because fewer parasitized nests were deserted and the probability of nest success was higher. Our study provides the first evidence that increases in cowbird productivity may be an unintended consequence of cowbird control programs, especially during the initial years of trapping when parasitism may only be moderately reduced. Thus, understanding the demographic impacts of cowbird removals requires an informed understanding of the behavioral ecology of host–parasite interactions.

1 aKosciuch, K.L.1 aSandercock, B.K. uhttps://esajournals.onlinelibrary.wiley.com/doi/abs/10.1890/07-0984.102567nas a2200229 4500008004100000245010800041210006900149300001300218490000800231520185700239653002502096653001502121653001402136653001502150653001902165653001702184653002002201100002102221700001702242700001902259856005902278 2008 eng d00aEffects of experimental cowbird removals on brood parasitism and nest predation in a grassland songbird0 aEffects of experimental cowbird removals on brood parasitism and a820 -8300 v1253 a

Brood parasitism and predation are two factors that limit seasonal fecundity in grassland songbirds. We removed Brown-headed Cowbirds (Molothrus ater) in a switchback experiment to examine the effects of brood parasitism and nest predation on the productivity of Dickcissels (Spiza americana). Nesting Dickcissels were monitored at four study plots in northeast Kansas in a two-year study. Brown-headed Cowbirds were captured with drop-in traps at two removal plots, two unmanipulated plots were reference plots, and treatments were reversed between years. To evaluate the effect of Brown-headed Cowbird removals, we compared the percentage of nests parasitized, rates of multiple parasitism, clutch size, daily nest survival rates, and overall productivity per nest between removal and reference plots. Removals of Brown-headed Cowbirds successfully reduced the probability of parasitism and rates of multiple parasitism, but only in one of two years. Brown-headed Cowbirds did not appear to contribute to nest losses, given that few nests were abandoned because of cowbird activity and that the probabilities of nest parasitism and nest survival declined simultaneously over the breeding season. Overall, nest productivity showed no difference between treatments in either year, despite reduced rates of parasitism at removal plots in 2004. High rates of nest predation minimized the potential benefits of Brown-headed Cowbird removals for increasing productivity of Dickcissels. Our results demonstrate that removals can reduce parasitism levels but that the success of removal programs may vary annually, particularly in regions where Brown-headed Cowbirds and nest predators are abundant. Management actions that minimize parasitism and predation by modifying habitat structure may provide better alternatives to programs based on removals.

10abrown-headed cowbird10aDickcissel10afecundity10amanagement10aMolothrus ater10aproductivity10aSpiza americana1 aSandercock, B.K.1 aHewett, E.L.1 aKosciuch, K.L. uhttps://academic.oup.com/auk/article/125/4/820/514820602071nas a2200145 4500008004100000245012100041210006900162300001300231490000700244520154000251100001901791700001701810700002101827856007701848 2008 eng d00aStable isotopes identify the natal origins of a generalist brood parasite, the brown‐headed cowbird Molothrus ater0 aStable isotopes identify the natal origins of a generalist brood a364 -3670 v393 a

Identifying the natal origins of brood parasites is a major challenge that usually requires labor-intensive searching for nests of host species. Stable isotope analysis of feathers and other body tissues of parasitic young could be a possible tool for determining natal origins if tissues reflect the isotopic composition of the diet fed to nestlings. We measured the carbon (13C) and nitrogen (15N) isotope compositions of feathers for two age-classes of brown-headed cowbirds Molothrus ater at the Konza Prairie Biological Station near Manhattan, Kansas: nestlings raised by five species of songbird hosts in two different habitats, and juveniles captured after independence. Isotope values from cowbird nestlings did not differ among host species and we were unable to assign juvenile cowbirds to their natal hosts. However, nestlings raised in grassland habitat had feathers that contained significantly higher δ13C values and lower δ15N values than nestlings raised in shrub habitats. In addition, independent juveniles had isotopic signatures that were similar to cowbird nestlings raised on shrub habitats. Although dickcissel Spiza americana comprised the majority of samples from shrub habitats, our conclusions reflect the natural pattern of parasitism at the site and should be representative of cowbirds raised at Konza. We conclude that stable isotope analysis of feathers is effective for determining the natal origins of parasitic young if isotope values from nestlings are isotopically distinct among habitats.

1 aKosciuch, K.L.1 aRivers, J.W.1 aSandercock, B.K. uhttps://onlinelibrary.wiley.com/doi/abs/10.1111/j.0908-8857.2008.04170.x00427nas a2200121 4500008004100000245006000041210005900101260004300160300001100203490002100214100001900235856005100254 2006 eng d00aHost-parasite interactions on an experimental landscape0 aHostparasite interactions on an experimental landscape aManhattan, KSbKansas State University a1 -1060 vPhD Dissertation1 aKosciuch, K.L. uhttp://krex.k-state.edu/dspace/handle/2097/18602302nas a2200229 4500008004100000245009000041210006900131300001300200490000700213520153200220653001701752653002501769653001801794653002101812653003201833653001901865653001701884100001901901700001701920700002101937856011401958 2006 eng d00aNest desertion bya cowbird host: an anti-parasite behavior or a response to egg loss?0 aNest desertion bya cowbird host an antiparasite behavior or a re a917 -9240 v173 aNatural selection can favor songbirds that desert nests containing eggs of the parasitic brown-headed cowbird (Molothrus ater). However, the high variability in desertion of parasitized nests within species is perplexing in light of the typically high costs of parasitism. Because nest desertion can also be a response to partial clutch predation, we first asked if Bell's vireos (Vireo bellii) deserted nests in response to the presence of cowbird eggs (antiparasite response hypothesis) or to egg removal by predators and female cowbirds (egg predation hypothesis). Second, we asked whether variation in nest desertion was due to intrinsic differences among individuals or to variation in nest contents. We monitored a large number of nests (n = 494) and performed a clutch manipulation experiment to test these hypotheses. The number of vireo eggs that remained in a nest was a strong predictor of desertion both within and among pairs. Neither the presence of a single cowbird egg, which leads to nest failure for this host, nor the number of cowbird eggs received in a vireo nest influenced nest desertion. Furthermore, vireos did not desert experimental nests when we immediately exchanged cowbird eggs for vireo eggs but deserted if we removed vireo eggs and replaced them with cowbird eggs the following morning. Desertion of parasitized nests by Bell's vireos can be almost entirely explained as a response to partial or complete clutch loss and does not appear to have been altered by selection from brood parasitism.10aBell's Vireo10abrown-headed cowbird10aegg predation10aevolutionary lag10ahost–parasite coevolution10aMolothrus ater10aVireo bellii1 aKosciuch, K.L.1 aParker, T.H.1 aSandercock, B.K. uhttp://lter.konza.ksu.edu/content/nest-desertion-bya-cowbird-host-anti-parasite-behavior-or-response-egg-loss