. The Canadian field-naturalist. Natural history. Letters Observations on the Decline and Survival of the Peregrine Falcon Probably all Peregrine Falcon {Falco peregrinus) populations in North America are endangered, by pesticides, although in the Queen Charlotte Islands of , southern Alaska, and parts of the boreal and tundra regions of the arctic, numbers are still relatively high. Unfortunately, several overly sim- plified statements have appeared in this Journal in recent months which only obscure the serious questions which must be resolved if the species is to be saved from total ext
. The Canadian field-naturalist. Natural history. Letters Observations on the Decline and Survival of the Peregrine Falcon Probably all Peregrine Falcon {Falco peregrinus) populations in North America are endangered, by pesticides, although in the Queen Charlotte Islands of , southern Alaska, and parts of the boreal and tundra regions of the arctic, numbers are still relatively high. Unfortunately, several overly sim- plified statements have appeared in this Journal in recent months which only obscure the serious questions which must be resolved if the species is to be saved from total extinction on this continent. I would like to indicate some of those aspects of the biology of the Peregrine that have to be borne in mind when we are considering how this species may be helped to survive. I would also like to dis- cuss some of the problems and some more hopeful aspects concerning the Peregrine. 1. A Non-breeding Surplus of Adult Falcons It has been suggested by Hickey (1942) and Cade (1968) that the reason that a lost member of a pair ( shot at nest cliffs) was so quickly replaced in years gone by was that there was a non-breeding surplus of adult falcons. Cade (1968: 239) states: "Evidently the falcon populations long ago evolved a social organization that strongly buf- fers the breeding pairs against numerical reduction, through the production of a large reservoir of sexually competent non-breeders, able to replace losses in the breeding population ; Therefore, it would appear that when we see an actual decline in the number of nesting pairs, the surplus (an unknown percentage of the population) may already have been exhausted. Those birds that continue to survive once the decline is underway are probably the ones with summering and winter- ing areas, migration routes, and perhaps even individual food habits, that have somehow until then spared them from accumulating lethal doses of biocides. Or, alternatively, the surviving falcons' paren
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