Latitudinal variation in clutch size-lay date regressions in Tachycineta swallows: effects of food supply or demography?

DAVID D. WINKLER; RINGELMAN, K.M.; DUNN, P.; WHITTINGHAM, L.; HUSSELL, D. J. T. ; CLARK, R. G. ; MASSONI, VIVIANA

ECOGRAPHY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2014

0906-7590

IMPORTANTE: no he listado todos los autores del trabajo (son 27 porque es un trabajo de una comunidad científica: la red de Golondrinas de las Américas). En ese orden yo estoy listada número 21.In a study of almost 16,000 nest records from seven swallow species across the entire WesternHemisphere, clutch sizes decline with relative laying date in each population, but the slope ofthis decline grows steeper with increasing distance from the equator. Late-laying birds at alllatitudes lay clutches of similar sizes, suggesting that latitudinal differences may be drivenprimarily by earlier-laying birds. Focused comparisons of site-years in North America withqualitatively different food availability indicate that food supply significantly affects mean clutchsize but not the clutch size-lay date regression. Other studies on the seasonality of swallow foodalso indicate that steeper clutch size-lay date declines in the North are not caused by steeperearlier food peaks there. The distribution of lay dates grows increasingly right-skewed withincreasing latitude. This variation in lay-date distributions could be due the predominance ofhigher quality, early-laying (and large-clutched) individuals among populations at higherlatitudes, resulting from latitudinal variation in mortality rates and the intensity of sexualselection. Our results underscore the importance of studying clutch size and lay date in tandemand suggest new research into the causes of their joint geographic variation.