XXI International Ornithological Congress, Vienna, Austria, August 1994.
A comparison of the breeding success of urban and rural American Crows, Corvus brachyrhynchos.
KEVIN J. MCGOWAN, Ecology & Systematics, Cornell Univ., Ithaca, NY 14853, USA.
American Crows, Corvus brachyrhynchos, have become common urban birds only in the last few decades. Changes in laws against firing guns in cities, as well as changes in human attitudes toward crows, may have made cities newly available as nesting habitat. With dependable food sources and perhaps fewer predators, urban areas could even be preferred for nesting over rural areas. A study of Corvus corone in Switzerland (1, 2) found that urban-nesting Carrion Crows had slightly higher nest success than those nesting in agricultural areas. The young produced, however, were of inferior quality and were unlikely to become breeders. In effect, the cities were attractive traps, allowing crows to breed but not replace themselves. I compared the breeding success of American Crows nesting in Ithaca, New York and the surrounding countryside. Urban crows nested earlier and at higher densities than rural crows. Nest success was equal between the areas, but rural nests produced larger young. Unlike urban Carrion Crows, urban American Crows were successful in becoming breeders. The increase in American Crow numbers seen over the last 25 years in eastern North America (3) may be due in part to the successful exploitation of urban nesting habitats. (1. Richner, H. 1989. J. Anim. Ecol. 58: 427. 2. Richner, H. 1990. Ibis 132: 105. 3. Robbins, C. et al. 1986. U.S. Fish Wildl. Serv. Resour. Publ. 157.)