The effects of habitat fragmentation on the golden-cheeked warbler (Texas)

Habitat fragmentation has been implicated in the declines of some species of migratory songbirds. Effects on species within the remaining fragments may result from habitat loss, reduced patch size, increased isolation, increased edge, and the nature of the surrounding landscape matrix. I investigated the effects of habitat fragmentation on the endangered Golden-cheeked Warbler (Dendroica chrysoparia) at 100 sites in central Texas from 1993 through 1995. I found positive relationships of patch size with both pairing success and reproductive success. The degree of isolation showed no apparent effects on warbler reproductive success. Distribution of warbler territories relative to the edge was bimodal with peaks at 0-50 m and 100-200 m. Reproductive success was greatest in territories farther than 100 m from the edge, leading to the conclusion the Golden-cheeked Warbler is slightly forest-interior. Fourteen land uses were identified adjacent to habitat patches, but agriculture and grasslands more commonly abutted occupied patches while both medium-density and high-density residential development more commonly occurred adjacent to unoccupied patches. Territorial placement within a patch appeared to be influenced by adjacent land uses, with warblers selecting agriculture and grasslands as the nearest land use, and selecting against commercial development, entertainment, forested non-warbler habitat, and high-density transportation. Lowest reproductive success occurred in territories closest to forested non-warbler habitat. Distance to the edge and territory size were greatest for territories closest to land uses with the highest levels of human disturbance. Insect availability may best explain many of the patterns observed while nest predation and brood parasitism appear to exert less influence on warbler distribution and reproductive success. Management recommendations include minimizing further fragmentation, minimizing the types of land uses which occur adjacent to occupied patches, providing a buffer zone of natural grassland around occupied patches, and minimizing the extent of edges.