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

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.