Golden-winged Warblers Vermivora Chrysoptera Research Articles

The effects of force-fledging and premature fledging on the survival of nestling songbirds

Despite the broad consensus that force-fledging of nestling songbirds lowers their probability of survival and therefore should be generally avoided by researchers, that presumption has not been tested. We used radiotelemetry to monitor the survival of fledglings of Ovenbirds Seiurus aurocapilla and Golden-winged Warblers Vermivora chrysoptera that we unintentionally force-fledged (i.e. nestlings left the nest in response to our research activities at typical fledging age), that fledged prematurely (i.e. nestlings left the nest earlier than typical fledging age), and that fledged independently of our activities. Force-fledged Ovenbirds experienced significantly higher survival than those that fledged independent of our activities, and prematurely fledged Ovenbirds had a similarly high survival to those that force-fledged at typical fledging age. We observed a similar, though not statistically significant, pattern in Golden-winged Warbler fledgling survival. Our results suggest that investigator-induced force-fledging of nestlings, even when deemed premature, does not necessarily result in reduced fledgling survival in these species. Instead, our results suggest that a propensity or ability to fledge in response to disturbance may be a predictor of a higher probability of fledgling survival.

Testing common assumptions in studies of songbird nest success

We studied Ovenbird Seiurus aurocapilla and Golden-winged Warbler Vermivorachrysoptera populations in northern Minnesota, USA, to test two common assumptions instudies of songbird nest success: (1) that the condition of an empty nest on or near itsexpected fledge date is an indicator of nest fate; and (2) that the presence of a fledgling orfamily group within a territory confirms a successful nest in that territory. We monitoredthe condition of nests and used radiotelemetry to monitor juveniles through the expectedfledging date and early post-fledging period. Of nests that contained nestlings 1–2 daysbefore the expected fledge date, fates were misidentified using nest condition alone for9.5% of Ovenbird nests, but those misidentifications were made in both directions (suc-ceeded or failed), yielding only a small bias in estimated nest success. However, 20% ofGolden-winged Warbler nests were misidentified as successful using nest condition duringthe final visit interval, biasing the nest success estimate upward by 21–28% depending onthe treatment of uncertain nest fates. Fledgling Ovenbirds from 58% of nests travelledbeyond their natal territory within 24 h, rising to 98% after 5 days, and those fledglingstravelled up to 390 m from nests within 10 days of fledging. Fledgling Golden-wingedWarblers from 13% of nests travelled beyond their natal territory within 24 h, rising to85% after 5 days, and those fledglings travelled up to 510 m from nests within 10 days offledging. We conclude that nest condition and fledgling presence can be misleading indica-tors of nest fate, probably commonly biasing nest success estimates upward, and we rec-ommend that these assumptions should be tested in additional species.Keywords: fledgling, Golden-winged Warbler, Ovenbird, Seiurus aurocapilla, telemetry,Vermivora chrysoptera.Estimates of songbird reproductive success, typi-cally limited to nest data, are used to assess habitatquality (e.g. Weinberg & Roth 1998), model pop-ulation dynamics (e.g. Podolski et al. 2007), iden-tify source and sink populations (e.g. Donovan etal. 1995), and inform conservation and manage-ment plans (e.g. Woodworth 1999). Althoughsongbird population growth may be generally moresensitive to adult annual survival and fledgling sur-vival (Donovan & Thompson 2001, Streby &Andersen 2011), population growth is also sensi-tive to variation in nest success (Donovan et al.1995), and nest success is the only directly esti-mated parameter in most studies of songbirdreproductive success (Anders et al. 1997). Manypopulation models account for re-nesting (birdsnesting again after initial failure) and estimates ofnest productivity (number of young produced persuccessful nest). All such studies require accuratefield identification of whether each monitored nestsucceeded or failed in producing young. However,observational studies of songbird nests often

Taxonomic recommendations for British birds: seventh report

Taxonomic recommendations for British birds: seventh report

Habitat quality and habitat selection of golden-winged warblers in Costa Rica: an application of hierarchical models for open populations

Summary 1. Identifying high-quality habitat is integral to effective species conservation efforts and requires information about habitat-specific abundance and demographics. This information is lacking for many species of conservation concern because of the inherent difficulties associated with implementing mark–recapture studies at large spatial scales. 2. The golden-winged warbler Vermivora chrysoptera is a Neotropical–Nearctic migratory bird experiencing a long-term population decline; yet no information about non-breeding season habitat quality or habitat selection exists to inform conservation efforts. We used a novel hierarchical model that requires only spatially and temporally replicated count data to estimate habitat-specific abundance, apparent survival, recruitment and detection probability of golden-winged warblers wintering in Costa Rica. We quantified habitat selection at the home-range level using radiotelemetry. 3. Golden-winged warblers were absent from tropical dry forest and were most abundant in premontane evergreen forest. Within their home ranges, golden-winged warblers selected microhabitat features associated with intermediate disturbance that reflected their preference for foraging in hanging dead leaves. 4. Consistent with other evidence of a declining population, local population size decreased over the duration of the study. The rate of decrease was higher during the non-breeding season than among seasons. We found no differences in apparent survival or recruitment among habitat types; however, our estimates of these parameters were imprecise. 5. Synthesis and applications. Golden-winged warblers are forest-dependent species during the non-breeding season and have specialized microhabitat requirements that make them vulnerable to ongoing tropical deforestation. However, advanced secondary forests can provide the requisite microhabitat features, and because we found no evidence of reduced survival in this habitat type, regenerating forest on degraded lands may be an effective component of a conservation strategy for this species. Our study also demonstrates that information on population dynamics and habitat quality can be obtained using repeated counts instead of mark–recapture methods.