Apparent selective advantage of leucism in a coastal population of southern caracaras (Falconidae)

PIM EDELAAR; JOSÉ DONAZAR; MATIAS SORIANO; MIGUEL ÁNGEL SANTILLÁN; DIEGO GONZÁLEZ-ZEVALLOS; PABLO GARCIA BORBOROGLU; NORA LISNIZER; ALEJANDRO JAVIER GATTO; MARÍA LAURA AGÜERO; CARLOS A. PASSERA; LUIS AUGOSTO EBERT; MARCELO BERTELOTTI; GUILLERMO BLANCO; MONICA ABRIL; GRACIELA ESCUDERO; FLAVIO QUINTANA

EVOLUTIONARY ECOLOGY RESEARCH

EVOLUTIONARY ECOLOGY LTD

Año: 2011 vol. 13 p. 187 - 196

1522-0613

Southern caracaras are medium-sized raptors with a large range stretching to the southern tip of South America. An aberrant, leucistic plumage is found commonly along the coast of Chubut Province (Patagonia, Argentina). Leucistic birds do not produce dark melanin in their feathers. However they are not albinos because their eyes 50 are not red. No genetic studies of caracara plumages are known. Hypothesis: The high frequency of leucistic birds in Chubut Province arises because of natural selection. Map the distribution of leucistic individuals relative to normal individuals. Combine a variety of anecdotal natural history observations, collected over twenty years, into a logical inference. Leucistic caracaras were found only along a 250 km stretch of rocky 60 oceanic islands and continental outcrops with large seabird colonies in Chubut Province. In the rest of their range, southern caracaras have dark plumage. Where they do occur, leucistic birds are frequent and co-occur with dark-plumaged birds. Intermediate individuals, presumably heterozygotes, exist. Leucism is not related to age or sex. Leucistic individuals are restricted to a particular habitat. Gene flow has not homogenized 65 the coastal and inland populations.