Post-fledging ecology of endangered Golden-cheeked Warblers

Abstract

Recently fledged birds often experience low survival as they undergo rapid changes in their behavior, (e.g., habitat use, mobility, and foraging rate). For species of conservation concern, information about the post-fledging period can be critical for effective management and conservation. We investigated the post-fledging ecology of endangered Golden-cheeked Warblers (Setophaga chrysoparia) in central Texas. Current management guidelines focus on nesting habitat even though songbird fledglings may use entirely different habitats. We radio-tracked fledglings (N = 23) to assess their habitat use, estimate daily survival, and observe age-based behavioral changes. Habitat used by fledglings was similar to adult nesting habitat and was dominated by Ashe juniper (Juniperus asheii; 75%) and oak (Quercus spp.; 21%). Apparent fledgling survival was 65%, and the estimated daily survival rate of fledglings during their first 4 weeks post-fledging was 0.985 (95% CI = 0.971–0.993). To investigate the factors associated with predation, we estimated survival while excluding mortality events due to exposure. Estimated survival was greater in areas with more junipers than oaks. As fledglings aged, use of oaks as foraging substrates increased as did their prey capture rates (nearly twice as many prey captured per hour in oaks than in junipers). Current management recommendations for nesting adult Golden-cheeked Warblers specify maintaining mature juniper–oak forests composed of ~70% juniper, a recommendation that also appears to accommodate fledglings. Fledgling Golden-cheeked Warblers acquire unique benefits from junipers (i.e., safety) and oaks (i.e., foraging opportunities), so management plans should include the maintenance of both junipers and oaks.