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John W. McNutt, A Peregrine Falcon Polymorph: Observations of the Reproductive Behavior of Falco kreyenborgi, The Condor: Ornithological Applications, Volume 86, Issue 4, 1 November 1984, Pages 378–382, https://doi.org/10.2307/1366810
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Abstract
Observations of the reproductive behavior and productivity of the South American Pallid Falcon, historically known as Kleinschmidt's Falcon (Falco kreyenborgi), confirm and amplify findings by Ellis and Peres G. (1983), that F. kreyenborgi may be described in terms of a dichromatic polymorph of F. peregrinus cassini, the South American subspecies of Peregrine Falcon. The pallid form occurs relatively frequently in the eastern zone of the southern tip of South America, where it is locally sympatric with F. p. cassini. This study describes mating behavior of 17 pairs and productivity of 15 pairs of falcons in this region of southern Patagonia. In five of these pairs, both the adults were phenotypically "normal" F. peregrinus; in two pairs, both were pallid; and in ten pairs, the adults were mixed: a normal adult peregrine mated with a pallid individual. Phenotypic expression of the pallid trait from productivity data indicates that the genetic basis for pallidism is recessive to the normal genotype. My analysis of gene frequencies, based on this assumption, demonstrates a high frequency of heterozygosity among the local breeding population, which is characteristic of a clinal variation maintained by either low gene flow or selection for the pallid genotype.
