The Influence of Tree Species Composition on Songbird Abundance and Productivity

Abstract

Most avian habitat selection studies are conducted within small spatial and temporal scales and fail to link habitat selection decisions to reproductive success. This limits our understanding of avian demographic patterns across the full continuum of ecological conditions a species inhabits and may result in the application of inappropriate conservation strategies. The golden-cheeked warbler (Setophaga chrysoparia; hereafter warbler) is a federally endangered songbird that breeds in oak-juniper woodland of central Texas. Management guidelines indicate that mature, dense Ashe juniper cover is an attribute of high quality warbler breeding habitat, but few studies have examined warbler responses to Ashe juniper across the continuum of vegetation types they inhabit. I used data collected from 899 territories on 90 study sites (2009–2013) located across the warbler’s breeding range to investigate the influence of year, geographic location, various Ashe juniper metrics, and dominant oak species on warbler abundance and productivity. My results reiterate that vegetation utilized by warblers is highly variable and that warblers successfully breed in areas with vegetation characteristics outside current descriptions of warbler breeding habitat. Warbler territory density remained constant across the full range of percent Ashe juniper cover in woodland dominated by Lacey (Quercus laceyi), live (Q. fusiformis), and Texas oak (Q. buckleyi). Warbler territory density increased with increasing percent Ashe juniper cover in woodland dominated by post oak (Q. stellata) and in mixed oak woodland and warbler territory density decreased with increasing percent Ashe juniper cover in woodland stands dominated by shin oak (Q. sinuata). Territories were larger in oak-juniper woodland stands dominated by live oak than oak-juniper woodland stands dominated by all other species but post oak. Results regarding relationships between territory-scale metrics and territory size and pairing and fledging success varied, but indicate that prioritizing sites based on qualitative Ashe juniper metrics or managing sites to promote single-aged stands of mature Ashe juniper cover may not be the most effective strategy for warblers. Management and restoration efforts may be more effective if tailored to local vegetation characteristics associated with tree species composition.