Origin, Growth, and Composition of the Recovering Peregrine Falcon Population in Ontario

Abstract

After an absence of more than two decades, Peregrine Falcons (Falco peregrinus) resumed nesting in Ontario in 1986. Between 1991 and 2006, at least 193 young fledged in southern Ontario and 548 young fledged in northern Ontario. The number of breeding pairs, nesting attempts, successful nests, and young fledged all steadily increased in both regions throughout this period. In southern Ontario, 25% of the breeding adults produced nearly 50% of all fledglings, and 87% of the fledglings came from just eight breeding sites. Direction of natal dispersal was variable, but females consistently moved farther than males, and there was frequent movement both to and from adjacent American states. The population recovery resulted from the release of 592 captive-bred F. p. anatum juveniles in Ontario between 1977 and 2005, plus immigration from other provinces and release efforts in adjacent regions of the United States, where at least five subspecies contributed to the gene pool of captive-bred birds. Encounter rates for both captive-bred and wild-fledged young in Ontario have been low, but wild-raised young have been recruited to the breeding population almost twice as frequently as captive-bred birds. This difference partially explains the genetic composition of the southern Ontario population, where at most 21% of nesting attempts between 1995 and 2006 involved a pair of Canadian-released anatum adults, and 59% of cases involved at least one adult of American origin. Therefore, although the Ontario population has exceeded documented historical levels, it may not be greater than actual historical numbers, and it cannot be strictly considered an anatum population.