American Ornithologists' Union Annual Meeting, Ames, IA, June 1992.
Cooperative breeding and reproductive success of American Crows in Ithaca, New York. Kevin J. McGowan, Section of Ecology & Systematics, Cornell University, Ithaca, NY 14853.
Although it is a common species, much remains to be discovered about the breeding biology of the American Crow (Corvus brachyrhynchos). In 1989, 1990 and 1991 over 120 nests were located in upstate New York, and nestlings were individually marked. More than half of the nests were attended by auxiliary helpers in addition to the breeding pair, with up to seven birds in attendance. Marked crows returned to help their presumed parents for several years. Over half to two-thirds of all nests succeeded in fledging young each year, but only 13% to 18% succeeded in fledging young from all eggs laid. High rates of both hatching failure and brood reduction were documented, surpassing predation as a source of nest content loss. Brood reduction frequently involved large nestlings lost within one week of fledging, at over 60% of adult body weight. Helpers significantly increased the number of fledglings produced in 1990 but not in 1991. Helpers may benefit breeders by providing more food in bad years, but their role in mitigating brood reduction is still unclear.