Jennifer L. Reidy

Golden-Cheeked Warbler Nest Mortality and Predators in Urban and Rural Landscapes

Abstract Predation is a major cause of nest failure for songbirds, yet information is lacking on the relative importance of predator species in different landscapes. We identified nest predators of Golden-cheeked Warblers (Dendroica chrysoparia) in an urban landscape, compared cause-specific mortality rates between urban and rural landscapes, and evaluated whether monitoring nests with cameras affected nest survival. We monitored 68 nests with cameras in Austin, Texas, during 2005, 2006, and 2008 to identify causes of mortality, including predators, in an urban landscape. The period mortality and predation rates were 0.60 (95% CI: 0.42–0.73) and 0.52 (95% CI: 0.37–0.68), respectively. We identified predators at 20 nests: Texas rat snakes (Elaphe obsoleta lindheimerii) depredated eight nests (40%), Western Scrub-Jays (Aphelocoma californica) depredated six (30%), Coopers Hawks (Accipter cooperii) depredated two (10%), fox squirrels (Sciurus niger) depredated three (15%), and fire ants (Solenopsis sp.) depredated one nest (5%). We compared mortality rates, predation rates, and predators of the 68 camera-monitored nests in Austin to 74 nests monitored with cameras in the rural landscape of Fort Hood, Texas, during 1997–2002 and 2005. The period mortality rate (0.63, 95% CI: 0.47–0.75), predation rate (0.59, 95% CI: 0.45–0.73), and predator composition at Fort Hood were similar to those in Austin. Nest abandonment, hatching success, and nestling survival were also similar in both landscapes. We compared nest survival of the 68 camera-monitored nests to 62 active nests monitored without video cameras in Austin; period nest survival was slightly higher for camera-monitored nests (0.40, 95% CI: 0.22–0.58) than for nests without cameras (0.37, 95% CI: 0.19–0.54).

Factors affecting golden-cheeked warbler nest survival in urban and rural landscapes

Abstract We evaluated hypotheses concerning temporal, landscape, and habitat effects on nest survival of golden-cheeked warblers (Dendroica chrysoparia) in an urban and a rural landscape during the breeding seasons of 2005 and 2006 in central Texas, USA. We found support for temporal effects of year and cubic effect of date and included them in candidate models that evaluated habitat and landscape effects. Nest survival was lower in 2006 than in 2005 and decreased nonlinearly as the breeding season progressed. We found support for edge effects with decreased nest survival nearer edges and in areas with increased open edge density (wooded habitat abutting open habitat) or decreased trail density. However, confidence intervals for the model-averaged odds ratios overlapped 1.0 for all edge variables. Overall daily survival rate was 0.964 (95% CI = 0.949–0.975), resulting in a 25-day period survival of 0.398 (95% CI = 0.269–0.524). Period survival in Austins urban landscape (0.399, 95% CI = 0.270–0.526) was similar to survival in Fort Hoods rural landscape (0.396, 95% CI = 0.261–0.528). Both landscapes likely support self-sustaining populations based on reasonable assumptions for adult survival and number of nesting attempts. We suggest that some large urban preserves can provide breeding habitat of comparable quality to rural locations and recommend protecting large parcels (>100 ha) of breeding habitat with limited fragmentation and reducing the amount of wooded edge abutting open habitat to ensure nest survival regardless of their landscape context.

THE EFFECTS OF TEMPERATURE ON NEST PREDATION BY MAMMALS, BIRDS, AND SNAKES

Abstract. Understanding how weather influences survival and reproduction is an important component of forecasting how climate change will influence wildlife population viability. Nest predation is the primary source of reproductive failure for passerine birds and can change in response to temperature. However, it is unclear which predator species are responsible for such patterns because predation events are rarely observed. We investigated whether temperature influenced predator-specific rates of nest predation by analyzing data from six prior studies conducted between 1997 and 2010 in Texas, Illinois, and Missouri that used constant-surveillance video systems to identify predators at the nests of Golden-cheeked Warblers (Setophaga chrysoparia), Blackcapped Vireos (Vireo atricapilla), Indigo Buntings (Passerina cyanea), and Acadian Flycatchers (Empidonax virescens). Rates of nest predation by snakes and birds increased as daily maximum temperatures increased, whereas predation by mammals was essentially invariant in response to temperature. The relative roles of physiological versus community-level mechanisms (e.g., abundance or behavior of predators and/or alternative prey) in driving the patterns we observed remain unclear, but our data point to the need to consider important biological interactions when forecasting the effects of climate change on songbird populations.

Comparison of Methods for Estimating Density of Forest Songbirds from Point Counts

ABSTRACT New analytical methods have been promoted for estimating the probability of detection and density of birds from count data but few studies have compared these methods using real data. We compared estimates of detection probability and density from distance and time-removal models and survey protocols based on 5- or 10-min counts and outer radii of 50 or 100 m. We surveyed singing male Acadian flycatchers (Empidonax virescens), cerulean warblers (Dendroica cerulea), Kentucky warblers (Oporornis formosus), Louisiana waterthrushes (Parkesia motacilla), wood thrushes (Hylocichla mustelina), and worm-eating warblers (Helmitheros vermivorum) in bottomland and upland forest across 5 states in the Central Hardwoods Bird Conservation Region during the breeding season in 2007 and 2008. Detection probabilities differed between distance and time-removal models and species detectabilities were affected differently by year, forest type, and state. Density estimates from distance models were generally higher than from time-removal models, resulting from lower detection probabilities estimated by distance models. We found support for individual heterogeneity (modeled as a finite mixture model) in the time-removal models and that 50-m radius counts generated density estimates approximately twice as high as 100-m radius counts. Users should be aware that in addition to estimating different components of detectability, density estimates derived from distance and time-removal models can be affected by survey protocol because some count durations and plot radii may better meet model assumptions than others. The choice of a method may not affect the use of estimates for relative comparisons (e.g., when comparing habitats) but could affect conclusions when used to estimate population size. We recommend careful consideration of assumptions when deciding on pointcount protocol and selection of analysis methods.

Nocturnal Predation of Females on Nests: An Important Source of Mortality for Golden-Cheeked Warblers?

Abstract We monitored 124 female Golden-cheeked Warblers (Dendroica chrysoparia) at 133 nests with video cameras from 1997–2002 and 2005– 2006 at two study areas in central Texas, USA. Six adult females were depredated by snakes in 781 camera-monitored intervals when females were on the nest at night and exposed to possible nocturnal predation. Daily nest survival was 0.971 (95% CI: 0.959–0.980) and daily adult female predation while nesting was 0.008 (95% CI: 0.003–0.017). We estimated that 14.6% of breeding females were depredated on the nest during the breeding season based on the observed survival rates and assuming females whose first nest was unsuccessful and which survived attempted a second nesting attempt. Females were captured 75% of the times they were on the nest at the time of a nocturnal nest predation by a snake. Predation of nesting females is potentially an important source of mortality for Golden-cheeked Warblers, and warrants further investigation.

Eastern Wood-Pewee (Contopus virens) Breeding Demography Across a Gradient of Savanna, Woodland, and Forest in the Missouri Ozarks

ABSTRACT. Better knowledge of bird response to savanna and woodland restoration is needed to inform management of these communities. We related temporal and habitat variables to breeding demography and densities of the Eastern Wood-Pewee (Contopus virens) across a gradient of savanna, woodland, and forest. We determined nest success, clutch size, young fledged, and breeding densities and evaluated support for relationships with year, nest stage, date, nest height, tree cover, and percent forest in a 10-km radius. One hundred and twenty-eight of 310 nests (41.3%) fledged young. The most supported nest-survival model included nest stage and percent forest in the landscape. Daily nest survival was greater in the incubation than in the nestling stage and increased substantially with decreasing forest in the landscape. Four nests (1.3%) were parasitized by Brown-headed Cowbirds (Molothrus ater). Eastern WoodPewee density increased 83% over a range of 10–170% tree cover (percent tree stocking). Increased nest success with decreasing forest in the landscape indicates that Eastern Wood-Pewees are not highly susceptible to forest-fragmentation effects in the Missouri Ozarks, probably because they were not very susceptible to brood parasitism. The absence of any strong relationships between habitat measures and nest success, clutch size, or young fledged is in contrast to the large increase in density over the range of tree cover and is further evidence that variation in bird density does not always correspond to similar patterns in productivity.

Feeding Rates, Double Brooding, Nest Reuse, and Seasonal Fecundity of Eastern Wood-Pewees in the Missouri Ozarks

Abstract Despite being widespread and abundant, little is known about the breeding ecology and natural history of the Eastern Wood-Pewee (Contopus virens), in part because nests are often high in the canopy, difficult to view, and adults are monomorphic. We monitored nests of Eastern Wood-Pewees and recorded the feeding rate of nestlings by adults as part of a larger study on breeding demography of Eastern Wood-Pewees across a gradient of savanna, woodland, and forest in the Missouri Ozarks in 2010–2011. We monitored 287 nests between 26 May and 22 August and conducted feeding rate observations for 54 nests with nestlings. There was an 88-day nesting season with peaks of nest activity on 24 June and 22 July. We recorded 19 cases of double brooding and nine cases of within-season nest reuse. Seasonal fecundity was 2.2 fledglings per territory. The frequency of parental feeding visits increased with nestling age. These are additional observations of nest reuse, nesting cycle lengths, and breeding season length for Eastern Wood-Pewees; future demographical research of marked individuals will continue to fill in gaps in breeding ecology for this common and widespread flycatcher.

Demographic rates of Golden-cheeked Warblers in an urbanizing woodland preserve

ABSTRACT Knowledge of demographics is important in conservation planning for endangered species. We monitored the endangered Golden-cheeked Warbler (Setophaga chrysoparia) at a large, discontinuous preserve in an urbanizing landscape in central Texas, USA, to estimate survival and productivity. We estimated adult male survival using a spatial Cormack-Jolly-Seber model that separated emigration from mortality by incorporating location data from resightings. Annual male survival varied from 0.45 to 0.67 from 2010 to 2015 (posterior mean ± SD = 0.57 ± 0.06). Sixty-seven percent of resighted males moved <100 m among years, but a large minority of males moved far enough across years that dispersal should be accounted for in future survival analyses. Mean predicted seasonal productivity varied from 2.32 to 3.18 fledglings territory−1 from 2011 to 2015 (mean ± SD = 2.46 ± 0.51). Seasonal productivity was best predicted by the proportion of total woodland land cover in a 1 km radius around the annual median location, total edge density in a 1 km radius, and the standard deviation of canopy height in a 100 m radius. Seasonal productivity peaked at high proportions of total woodland cover, and decreased with increasing edge and canopy height standard deviation. Annual trends for survival and productivity were similar; that is, survival and productivity were above or below average in the same years, which could have important implications for population stability. Our estimated demographic rates are within the range of those reported from the best long-term data, from Fort Hood, Texas, and support the need for large patches of nonfragmented, mature woodlands to provide high-quality breeding habitat for this species.

Songbird Nest Survival in Managed Oak Savannas and Woodlands in the Missouri Ozarks

Abstract Midwestern savannas and woodlands were once dominant transitional communities but are now considered endangered. Savanna and woodland habitat is being restored and managed throughout the central and east-central portions of the United States, but few studies have investigated the effects of management on songbird nest survival. We monitored songbird nests in managed savanna and woodland sites in southern Missouri from 2009 to 2011 to estimate nest survival and to predict the relationships between nest survival and temporal, vegetation structure, and nest site variables. Daily nest survival was generally higher for the four canopy-nesting species, Acadian flycatcher (Empidonax virescens), blue-gray gnatcatcher (Polioptila caerulea), Eastern wood-pewee (Contopus virens), and summer tanager (Piranga rubra) (0.96-0.98), than the four shrub-nesting species, field sparrow (Spizella pusilla), indigo bunting (Passerina cyanea), prairie warbler (Setophaga discolor), and yellow-breasted chat (Icteria virens) (0.92-0.95), for which we estimated survival rates. In general vegetation structure around the nest had little influence on nest survival, except for canopy cover, which occurred in the top model set for four species. Nest survival of yellow-breasted chats was much higher in areas of lower canopy cover, whereas nest survival of Eastern wood-pewees was moderately lower and indigo buntings and summer tanagers peaked at low and intermediate levels of canopy cover, respectively. Therefore, savanna and woodland management, which tends to open the tree canopy, may benefit some bird species in this forested landscape, particularly those associated with low to intermediate canopy cover.