Migration and life-history reversal in Cliff Swallows (Petrochelidon pyrrhonota) breeding in South America

ARETA JI

Congreso; XI Neotropical Ornithological Congress; 2019

A major challenge to our understanding of animal migration is grasping the relative importance of genetically determined behaviors and behavioral plasticity. Migratory behaviors in birds are thought to be primarily under genetic control, and clearly many aspects of migration are necessarily innate. Although there is considerable research into the genetic basis for migration, the extent of deterministic genetic control, environmental influence and/or individual decision-making in the control of migration remains unclear. Worldwide we know of few occasions wherein migratory species have undergone rapid and dramatic life-history changes resulting in novel migration strategies. A case in point is trans-hemispheric breeding colonization, wherein a subpopulation suddenly begins breeding on what once was its wintering ground. These rare life-history reversals demand concomitant changes in migration, feather molt, and breeding behavior if the population is to remain viable. Cliff Swallows historically breed in North America and overwinter in South America, but in 2015 a small breeding colony established itself in Argentina. We tracked the movements of these birds documenting a complete reversal of the normal migration pattern, an apparent shift of molt phenology by approximately 6 months, and a new intra-South America migration, all of which arose within a single generation. Even when two birds returned to potential breeding areas in North America, we demonstrate that South American Cliff Swallows do not practice migratory double-breeding. Contrary to traditional thinking, rapid life-history changes suggest a secondary role of the genetic makeup of individuals in the emergence of novel migratory patterns, and indicate that phenotypic plasticity can allow for profound changes in the life-histories of migratory birds.