POPULATION STATUS AND RECENT TRENDS IN CANADIAN RAPTORS - A REVIEW

We examined population trends and status in 37 taxa of Canadian raptor s using Breeding Bird Survey (BBS) data (1966-1994 and 1985-1994) for the whole of Canada and seven ecozones separately, continent-wide Chri stmas Bird Counts (CBC) (1959-1988), migration counts from 12 hawkwatc hes (various dates) and specific research projects. According to the p rimary sources reviewed, many raptor populations increased since the e arly 1970s, coinciding with reductions in use of organochlorine pestic ides (OCs). Species that increased included osprey Pandion haliaetus, bald eagle Haliaeetus leucocephalus (BBS and CBC) and peregrine falcon Falco peregrinus anatum (1995 peregrine falcon survey). Red-tailed ha wk Buteo jamaicensis, American kestrel Falco sparverius and merlin Fal co columbarius also generally increased or were stable, but results di ffered according to source, time period and ecozone (both red-tailed h awk and American kestrel showed short-term decreases in the Mixedwood Plains BBS). Significant declines were found for burrowing owl Speotyt o cunicularia (BBS), short-eared owl Asio flammeus and long-eared owl Asio otus populations (BBS and CBC). Golden eagle Aquila chrysaetos ma y be declining in some areas (CBC, four migration counts) but results were equivocal; there was some evidence to suggest that broad-winged h awk Buteo platypterus may also be declining. Long-term BBS data indica ted that Swainson's hawk Buteo swainsoni populations were stable, but significant short-term declines were found in the Prairies ecozone, co rresponding with decreases in productivity measured in long-term breed ing studies. Sharp-shinned hawk Accipiter striatus apparently increase d in number according to the overall long-term BBS, but may be declini ng according to some eastern migration count data. While no evidence o f declines was found for prairie falcon Falco mexicanus, the Canadian population is small and vulnerable to habitat change that could reduce prey populations. Four species that reach their greatest abundance in , or are restricted to, the Prairies and Boreal Plains ecozones are de clining there (northern harrier Circus cyaneus, Swainson's hawk, burro wing owl and short-eared owl). Although causal factors vary, our analy sis suggests the possibility that large-scale phenomena such as human activity (pesticide use or habitat modification) and perhaps climate a re affecting populations of some Prairie raptors. Research on endanger ed species is being conducted under the auspices of national recovery plans. We recommend that research be instigated to examine critically productivity failures in Swainson's hawks, and possible declines in go lden eagle breeding populations. In view, of the increasingly wide-spr ead impact of forestry on northern forests in Canada, we further recom mend that special surveys be set lip, and breeding densities, producti vity and occupancy rates be determined in different forest types for a ccipiters, broad-winged hawk, as well as forest owls (particularly bar ren owl Strix varia, boreal owl Aegolius funereus and northern saw-whe t owl Aegolius acadicus brooksi). We caution that the BBS and other na tional surveys may be inadequate for monitoring populations of many ra ptor species in Canada, particularly forest-dwelling accipiters, some owls and buteos. Special monitoring or sampling programs are needed fo r these species. However, taken together, multiple sources can provide inferential evidence for population trends and status. (C) 1997 Elsev ier Science Ltd.