Nesting Success of Acadian Flycatchers (Empidonax Virescens) in Floodplain Forest Corridors

Reconnecting forest patches, including those of floodplain forest, often involves the creation of long, narrow corridors that have the potential to act as ecological traps for wildlife. We examined the effect of forest width and habitat composition of the landscapes immediately around nest patches on survival and parasitism of 359 Acadian Flycatcher (Empidonax virescens) nests in the Cache River Bioreserve in southern Illinois. Nests were distributed among 19 floodplain forest corridors along a small river system that is being restored and reconnected along its original floodplain. The corridors spanned a range of widths (80–3,170 m) and varied with the presence or absence of natural water-related habitats (beaver ponds, backwater swamps, and creeks). Although nest success varied slightly between stages of the breeding cycle, confidence intervals overlapped, which suggests constant nest success throughout the breeding cycle. Nest survival was relatively high by regional standards but did not vary significantly with any of the landscape variables measured. Contrary to predictions, probabilities of brood parasitism decreased with increasing proportions of anthropogenic habitats surrounding nests. Probabilities of brood parasitism also decreased, but only slightly, as the breeding season progressed. Finally, Acadian Flycatcher nests were located significantly more often near natural (forest-water interface) edges than expected at random. Narrow corridors such as those along floodplain restoration projects do not necessarily create ecological traps for all forest species. Acadian Flycathcers, however, are one of the only forest-nesting Neotropical migrants that nest in narrow corridors and, therefore, may be less vulnerable to negative effects of fragmentation. Éxito de Nidificación de Empidonax virescens en Corredores de Bosque de Planicies Inundables

A Removal Model for Estimating Detection Probabilities From Point-Count Surveys

Use of point-count surveys is a popular method for collecting data on abundance and distribution of birds. However, analyses of such data often ignore potential differences in detection probability. We adapted a removal model to directly estimate detection probability during point-count surveys. The model assumes that singing frequency is a major factor influencing probability of detection when birds are surveyed using point counts. This may be appropriate for surveys in which most detections are by sound. The model requires counts to be divided into several time intervals. Point counts are often conducted for 10 min, where the number of birds recorded is divided into those first observed in the first 3 min, the subsequent 2 min, and the last 5 min. We developed a maximum-likelihood estimator for the detectability of birds recorded during counts divided into those intervals. This technique can easily be adapted to point counts divided into intervals of any length. We applied this method to unlimited-radius counts conducted in Great Smoky Mountains National Park. We used model selection criteria to identify whether detection probabilities varied among species, throughout the morning, throughout the season, and among different observers. We found differences in detection probability among species. Species that sing frequently such as Winter Wren (Troglodytes troglodytes) and Acadian Flycatcher (Empidonax virescens) had high detection probabilities (∼90%) and species that call infrequently such as Pileated Woodpecker (Dryocopus pileatus) had low detection probability (36%). We also found detection probabilities varied with the time of day for some species (e.g. thrushes) and between observers for other species. We used the same approach to estimate detection probability and density for a subset of the observations with limited-radius point counts.