Cliff Swallows (Petrochelidon pyrrhonota) breeding in South America: Early phases in a trans-hemispheric colonization

GORLERI F; ARETA JI

Congreso; XI Neotropical Ornithological Congress; 2019

Occasionally, northern hemisphere migratory birds begin breeding at their southern hemisphere non-breeding range. This requires drastic phenological shifts for the individuals involved because it entails a reordering of the species? usual annual cycle of breeding, molt, and migration. Only populations that can quickly accommodate these changes will persist. In 2015, Cliff Swallows underwent trans-hemispheric colonization when a colony in Villa María, Córdoba, Argentina, produced young in South America for the first time. We monitored these Cliff Swallows during the first four breeding seasons. The geographic range of the population has shifted locally, as new colonies have formed, and others disappeared, but by the fourth breeding season a single colony of 6 nests was active. The timing of breeding initiation advanced over three years. Breeding individuals were not molting, but some showed unusual molt limits (old inner primaries) previously undescribed in Cliff Swallows, suggesting a previous interruption of molt to undergo breeding in South America. Some of the birds with molt limits no longer showed them by the following year when they were recaptured. The fact that life-history adjustments have occurred rapidly, within two years of the initial colonization event, suggests that these adjustments were mediated by plasticity in the timing of molt and breeding. Members of both recognized subspecies groups, melanogaster (red-fronted) and pyrrhonota (white-fronted), overwinter in Argentina. Measurements and forehead color indicate that the Argentine breeding population belongs to the pyrrhonota group and possibly to subspecies pyrrhonota. The geographically dispersed and more or less simultaneous breeding attempts here reported suggest that North American Cliff Swallows may be independently and repeatedly initiating breeding colonies in South America. Understanding how migratory birds adjust to major phenological shifts will inform how migration can affect geographic range in migratory birds and improve our understanding of determinants of long-distance colonization.