Habitat selection by juvenile black-capped vireos following independence from parental care

Abstract

If differences in ecological requirements result in juvenile birds using different habitats from breeding birds, then habitat management to protect those birds must protect both breeding and post‐breeding habitats. We examined habitat selection by juvenile black‐capped vireos (Vireo atricapilla) following their independence from parental care, in 2010–2013 on Fort Hood Military Reservation in central Texas, USA. The black‐capped vireo is a federally endangered species that nests almost exclusively in shrub vegetation, but previous anecdotal observations indicate that juveniles may prefer riparian vegetation. We used mist‐net capture rates and radio‐telemetry to determine relative abundance of juvenile vireos across habitats, to quantify movement patterns and habitat selection, and to investigate how vegetation density and arthropod abundance influenced habitat selection. We captured juveniles at similar rates in shrub and riparian vegetation. Radio telemetry data indicated that juveniles selected riparian vegetation over most other available vegetation types, and tended to stay in riparian vegetation upon arrival. Juveniles selected areas characterized by more canopy cover, denser foliage, and more arthropods. Riparian vegetation provides this combination of features more than other vegetation types, indicating that cover and food are the basis for habitat selection by juveniles. Our results indicate that habitat conservation strategies for black‐capped vireos should include protection of riparian vegetation near breeding areas, and more generally, that avian conservation strategies that focus only on breeding areas may potentially overlook other key habitats. © 2014 The Wildlife Society.

Broad-scale habitat use by fledgling Black-capped Vireo

“…We walked the same transects used in the early breeding season and extended transects to include a 300-m buffer around the study site. We used 300 m as a conservative buffer based on the mean distance juvenile vireos move between consecutive locations (Dittmar et al 2014). We walked transects every 3-5 d from sunrise to 13:00.…”

“…We defined woodland cover as contiguous vegetation of oak-juniper and deciduous forest, which included limestone woodland, dry-mesic slope woodland, and riparian forest cover types but excluded oak mottes within shrubdominated cover. Despite vireo fledgling selection for riparian vegetation (Dittmar et al 2014), we aggregated riparian forest with other cover types because it comprised just 8% of the total woodland in the study area. Using ArcGIS 10.0 (ESRI 2010), we created a 300-m buffer around the minimum convex polygon of all the fledgling locations at each study site, which defined the boundaries of what we considered to be available postfledging habitat.…”

“…Prior research in our study area suggests that arthropod abundance and biomass decline within vireo breeding habitat as the breeding season progresses (Morgan 2012). Woodlands may supply vireo fledglings with a perpetual abundance of prey (Dittmar et al 2014) and protective cover from predators and heat during the later stages of summer (e.g., Brokaw and Lent 1999). As such, we predicted that vireo fledgling use of woodland cover would increase, and distance from vireo detections to woodland would decrease, over time and as fledglings age.…”

“…Young vireos rely on their parents for food and tend to remain within the natal territory during the first few weeks postfledging (Graber 1961). Once independent, juveniles select for shrubland vegetation over forest and grass vegetation (Dittmar et al 2014) and forage in shrubs and trees < 3 m in height (Houston 2008). However, observations from various sites across the breeding range in central Texas indicate that independent vireo fledglings may disperse out of their territories into woodlands (Houston 2008, Pope et al 2013, shaded ravines (Graber 1961), and riparian forests (Dittmar et al 2014) during the postfledging period.…”

“…Once independent, juveniles select for shrubland vegetation over forest and grass vegetation (Dittmar et al 2014) and forage in shrubs and trees < 3 m in height (Houston 2008). However, observations from various sites across the breeding range in central Texas indicate that independent vireo fledglings may disperse out of their territories into woodlands (Houston 2008, Pope et al 2013, shaded ravines (Graber 1961), and riparian forests (Dittmar et al 2014) during the postfledging period. Additionally, as juvenile vireos age, they become less vulnerable to predation than younger fledglings and occupy a wider array of vegetation conditions while foraging (Walker 2015).…”