Effects of tree species composition and foraging effort on the productivity of golden-cheeked warblers
Authors: M. E. Marshall
The concept of habitat quality is fundamental to the study of ecology. Ecologists have long recognized the importance of vegetation structure and composition in the assessment of wildlife habitat. Vegetative characteristics affect productivity in birds for a variety of reasons (e.g., predator assemblages, nesting sites, song perches, food availability). This research investigated the relationship between habitat quality and prey availability and the effect these parameters have on reproductive success in golden-cheeked warblers (Dendroica chrysoparia). The objectives were to: 1) Determine any differences in pairing and fledging success of warbler territories within two ecosites exhibiting two distinctive tree species composition, 2) Explore the relationship between tree species composition, arthropod density, and foraging effort, and the effect these parameters have on reproductive success in golden-cheeked warblers, and 3) Investigate the connection between preferred foraging substrates and changes in arthropod abundance within golden-cheeked warbler territories throughout the breeding season. Individual warbler territories were mapped out and searched for fledglings, foraging behavior observed, and arthropods collected, to determine productivity, foraging effort, and food availability. These methods were conducted over two seasons in juniper-oak woodlands on Fort Hood, north-central Texas within 347 territories of two vegetative types: those marked by the predominance of post oak (Quercus stellata) and those marked by the predominance of Texas oak (Quercus buckleyi).
Pairing and fledging success of territories differed substantially between the two vegetative types. Movement rates differed considerably between the two vegetative types, indicating a difference in prey encounter rate. Foraging data indicated a clear switch in preferred foraging substrates from oak species early in the breeding season, to Ashe juniper (Juniperus ashei) in mid-May. Arthropod sampling revealed a correlation between preferred foraging substrates and arthropod density. Results suggested that Texas oak was an important foraging substrate for golden-cheeked warblers, and territories that lack this tree species generally did not succeed in fledging young. This study can be used to indicate areas that should be targeted for conservation by local, state, and federal government because they provide high quality habitat based on warbler productivity.
Marshall, M. E. 2011. Effects of tree species composition and foraging effort on the productivity of golden-cheeked warblers. Thesis, Texas A&M University, College Station, Texas, USA