Heather A. Mathewson

Understanding nest success and brood parasitism in the endangered Black-capped Vireo: comparisons with two sympatric songbirds

Abstract Nest predation and brood parasitism likely cause declines in many songbird species, yet the rate of these declines varies among species. Simultaneously studying co-occurring species with overlapping territories provides an opportunity to identify differences among the species that may explain differential reproductive success. We monitored nests of three co-occurring songbird species to determine whether the federally endangered Black-capped Vireo (Vireo atricapilla) experienced lower reproductive success than Northern Cardinals (Cardinalis cardinalis) and White-eyed Vireos (V. griseus) on private lands with and without trapping of brood parasites. We assessed if habitat metrics and nesting phenology were associated with nest success and frequency of brood parasitism by Brown-headed Cowbirds (Molothrus ater) to determine if these characteristics explain poor reproductive success. We monitored 188 nests in shrubland and ecotones with woodlands in central Texas from 2006–2008. We found species-specific differences in nest success and brood parasitism, year effects, and differential impacts of cowbird trapping. Black-capped Vireos nesting in locations without cowbird trapping experienced the lowest daily survival rate of nests (0.86) and period nest survival (0.01), whereas estimates in locations with cowbird trapping were similar to the other species (0.93 for daily and 0.11 for period nest survival). Nest initiation date was important for predicting brood parasitism, showing high probability of brood parasitism in the middle of the breeding season and low probability during the beginning and end of the season. Habitat metrics were not good predictors of nest success or brood parasitism. Management for conservation of Black-capped Vireos focused on vegetation manipulation may not increase reproductive success in the absence of cowbird trapping in some areas of the breeding range, because daily survival rate of nests was associated with cowbird trapping but not habitat metrics.

A before–after control–impact assessment to understand the potential impacts of highway construction noise and activity on an endangered songbird

Abstract Anthropogenic noise associated with highway construction and operation can have individual‐ and population‐level consequences for wildlife (e.g., reduced densities, decreased reproductive success, behavioral changes). We used a before–after control–impact study design to examine the potential impacts of highway construction and traffic noise on endangered golden‐cheeked warblers (Setophaga chrysoparia; hereafter warbler) in urban Texas. We mapped and monitored warbler territories before (2009–2011), during (2012–2013), and after (2014) highway construction at three study sites: a treatment site exposed to highway construction and traffic noise, a control site exposed only to traffic noise, and a second control site exposed to neither highway construction or traffic noise. We measured noise levels at varying distances from the highway at sites exposed to construction and traffic noise. We examined how highway construction and traffic noise influenced warbler territory density, territory placement, productivity, and song characteristics. In addition, we conducted a playback experiment within study sites to evaluate acute behavioral responses to highway construction noises. Noise decreased with increasing distance from the highways. However, noise did not differ between the construction and traffic noise sites or across time. Warbler territory density increased over time at all study sites, and we found no differences in warbler territory placement, productivity, behavior, or song characteristics that we can attribute to highway construction or traffic noise. As such, we found no evidence to suggest that highway construction or traffic noise had a negative effect on warblers during our study. Because human population growth will require recurring improvements to transportation infrastructure, understanding wildlife responses to anthropogenic noise associated with the construction and operation of roads is essential for effective management and recovery of prioritized species.

The Influence of Meadow Moisture Levels on Activity of Small Mammal Nest Predators in the Sierra Nevada, California

Abstract High nest predation rates are one of the main sources of nesting failure in passerines. Mountain meadows in the Sierra Nevada have been intensively modified, reducing meadow wetness and potentially favoring easy access for mammalian predators to reach nesting areas in the meadow interior. We conducted mammal trapping in wet and dry areas of montane meadows during May through August of 2007 and 2008 to identify the assemblage of potential mammalian nest predators and determine the relationship between activity and meadow wetness. Chipmunk (Tamias spp.) activity was primarily restricted to dry areas. Activity of Yellow-pine Chipmunks (Tamias amoenus) was >90% higher in dry versus wet areas. Deer Mice (Peromyscus maniculatus) were equally active in both site types in 2007, but declined and were only captured in wet areas in 2008. Overall activity was higher in 2007 and 2008 for both wet and dry areas (68% and 52%, respectively). Our results suggest that increasing the proportion of inundated areas in meadows may reduce small mammal activity (for instance Yellow-pine Chipmunks) and potentially reduce nest predation.

The Influence of Temperature on Black-Capped Vireo Nest-site Selection

Abstract Reproductive success is highly influenced by nest-site selection for avian species in breeding habitats, and variation in the physical environment can drive small-scale changes in the nest-site selection process. We examined the influence of temperature on Vireo atricapilla (Black-capped Vireo; hereafter Vireo) nest-site selection at Kerr Wildlife Management Area (KWMA) in Kerr County, TX (March–July 2013 and 2014). We measured ambient temperature across points that represented the continuum of vegetation characteristics used by Vireos at our study sites during the breeding season. We also found and monitored 181 Vireo nests, collected vegetation data, and compared vegetation characteristics between areas used and not used by Vireos. Finally, we investigated whether Vireo nest-site characteristics changed over the course of the breeding season in relation to the temperature profile of vegetation at our study sites. As expected, temperature increased over the course of the breeding season. Vireo nest sites had higher percent shrub cover than areas not used for nesting by Vireos. Vireos selected different vegetation characteristics for nesting as the breeding season progressed, but we did not find differences in temperature across vegetation types, suggesting that temperature is not the driving factor in Vireo nest-site selection in locations where temperatures remain consistently high throughout the breeding season. However, we could not directly measure temperature at nest-site locations. Therefore, Vireos may exhibit some degree of thermal preference at smaller spatial scales. Additionally, our results suggest that Vireos may require nesting habitat with more shrub cover than previously recommended.

Does Age Structure Influence Golden-Cheeked Warbler Responses Across Areas of High and Low Density?

Abstract. Age-based differentiation in the timing of avian migration can influence subsequent habitat use and, therefore, reproductive success. Over 2 breeding seasons, we compared arrival dates, pairing success, and fledging success for second-year (SY) and after-second-year (ASY) federally endangered Golden-cheeked Warblers (Setophaga chrysoparia) occupying areas of low (n = 9 sites) and high (n = 10 sites) warbler density. Male warblers arrived on low-density sites on average 6 days later (11 March) than high-density sites (5 March). Male warblers that established territories on low-density sites tended to be younger than male warblers that established territories on high-density sites. Overall pairing and fledging success were similar across low- and high-density sites, but overall pairing and fledging success were lower for SY males compared to ASY males; no SY birds fledged young on low-density sites. We found no difference in pairing or fledging success for ASY males at low- and high-density sites. For some species, habitat that supports fewer birds may be of lower quality. However, warblers in our study area fledged young at low- and high-density sites. As such, low-density sites may fill an important role in conservation efforts for this species.

Occurrence of western scrub-jays (Aphelocoma californica) near forest edges in fragmented golden-cheeked warbler (Setophaga chrysoparia) habitat

Abstract The western scrub-jay (Aphelocoma californica) is a common nest predator and has been documented depredating nests of the federally endangered golden-cheeked warbler (Setophaga chrysoparia), a woodland songbird, in central Texas. We conducted opportunistic and transect surveys for western scrub-jays across two vegetation classes (woodland and shrub-scrub) to investigate the proximity of scrub-jays to golden-cheeked warblers breeding in a fragmented landscape. We used a chi-square test to compare the number of observed and expected scrub-jay detections for each vegetation class. To investigate if scrub-jays are an edge-occupying species, we compared the distance to nearest vegetation edge of actual scrub-jay detections to a null distribution of mean random distances. We found that scrub-jays occur in areas closer to vegetation class boundaries but do not appear to prefer one vegetation type over the other. Our findings suggest that golden-cheeked warblers may have higher nest predation risk in fragmented areas of their breeding range.