Breeding biology of the White-rumped Swallows at Buenos Aires province, Argentina

VIVIANA MASSONI; FLORENCIA BULIT; JUAN CARLOS REBOREDA

IBIS

British Ornithologists' Union

Año: 2007 vol. 149 p. 10 - 17

0019-1019

We conducted a study of the breeding biology of the White-rumped Swallow Tachycineta leucorrhoa nesting in nestboxes in a flat, farming landscape in Buenos Aires Province, Argentina. White-rumped Swallow nesting attempts were detected from the end of September to mid December, with most clutches laid during October. This species laid clutches of four to six eggs with a mode of five eggs; most broods hatched synchronously (58 %), but hatching spread could last up to 4 days. Nestling growth curves adjust well to logistic functions, and at day 15 nestlings attain the asymptotic weight of 21.6g. Clutch size in White-rumped Swallows declined significantly as the season progressed. In addition, late season eggs were smaller and late season nestlings had a shorter nestling period and lower weight at day 15, probably leaving the nest lighter than early season nestlings. These data suggest that the swallows would benefit greatly from laying early in the season, which would provide nestlings with better survival prospects. However, both major sources of nest mortality, interspecific competition for nest sites and nestling mortality during bad weather, decreased through  the season. White-rumped Swallows follow the pattern found for other southern species, as it has smaller clutch size, lower growth rate, and remains longer at the nest than its North Hemisphere congener the Tree Swallow Tachycineta bicolor.