ABSTRACr.--Counts migrating hawks were initiated in 1934 at Hawk Mountain and, except for 1943-1945, have continued to the present. We analyzed the data from 1934-1986 by a standardized sample period appropriate for each species. Counts of several species known to be susceptible to detrimental effects of organochlorine pesticides crashed between 19461971. All of these populations recovered subsequently. The immature-age classes and the species with the shortest generation times recovered first after DDT use diminished in North America. These observations mostly conform to predictions made on the basis of the adverse effects of DDT and metabolites on raptors. We suggest that standardized migration counts reflect qualitative trends of most raptor populations that pass over Hawk Mountain in the autumn. Currently, populations of many species appear to be either stable or recovering from the effects of organochlorines. Possible exceptions are eastern populations of the Red-tailed Hawk (Buteo jamaicensis), American Kestrel (Falco sparverius), Broad-winged Hawk (B. platypterus), Red-shouldered Hawk (B. lineatus), and Golden Eagle (Aquila chrysaetos), which may be decreasing. Received 15 November 1988, accepted 28 July 1989. ANALYSIS of the population trends of birds has received attention recently because of observed and predicted regional or global changes in the environment and the availability of data suitable for long-term trend assessment (e.g.
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Bednarz et al. (1990) studied this question.