干旱区生态环境知识资源中心

Range change is occurring at a rapid rate for tropical, subtropical, and warns desert birds in Texas. Comparisons between former(1974) and current avian distributions for the region show significant breeding range extension of 40-220 km to the N, NE, or E for at least 68 species, many of which cross major biogeographic boundaries. Fieldwork at the northern end of the subtropics along the coastal plain of the Gulf of Mexico has provided extensive documentation of breeding populations in new areas (e.g., nests, eggs, nestlings, fledglings, pairs, singing males on territory, and response to playback) for nine subtropical species (e.g., Green Jay Cyanocorax yncas and White-tipped Dove Leptotila verreauxi), as well as photographic evidence of seasonal persistence derived from use of a novel, web-based collaborative online robotic wildlife camera. Poor previous documentation, population change, habitat loss in the former range, and habitat change in the new range are considered as possible explanations. We conclude that change in key parameters of habitat, e.g. seasonal food availability, as affected by factors related to climatic change, e.g., mean annual precipitation, temporal distribution of precipitation (monthly means), or monthly means for nighttime-low temperatures during the breeding season, provide the most likely explanations for observed range extensions. At present, movement of a large segment of the subtropical avian community into temperate habitats has not been met with a corresponding shift of temperate species as had been predicted by a number of models; rather the communities now overlap, creating, in effect, novel communities. Results of this overlap are likely to produce profound changes that may first be evident in the genetics of subtropical/temperate species pairs, e.g., Black-crested Titmouse Baeolophus atricapillus and Tufted Titmouse Baeolophus bicolor.