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 Just Accepted

This article has been peer reviewed and accepted for publication. It is in production and has not been edited, so may differ from the final published form.

New Guinean passerines have globally small clutch sizes

Benjamin Freeman, Nicholas Mason


Tropical birds have small clutch sizes. The mechanisms responsible for generating this pattern remain debated, and are typically considered by comparing tropical (small clutches) species to their temperate (large clutches) counterparts. However, variation in clutch size among tropical regions is seldom considered. We show that New Guinean forest passerines lay markedly smaller clutches (n= 102 species; mean ± sd = 1.52 ± 0.48) than other tropical avifaunas. While tropical species commonly lay two-egg clutches, a substantial number of New Guinean passerines appear to solely (38%) or frequently (24%) lay single-egg clutches. We used phylogenetic comparative methods to demonstrate that New Guinean passerines lay significantly smaller clutches than congeneric Southeast Asian species. We also show that reductions in clutch size have occurred multiple times among New Guinean passerines, suggesting phylogenetic constraint does not explain this pattern. Instead, current environmental factors, including strong parasitism or predation, may explain why New Guinean passerines lay small clutches. We conclude that clutch size variation between tropical regions offers a valuable opportunity to test drivers of clutch size variation, such as parasitism and predation, originally developed within a tropical-temperate framework.

MU14023  Accepted 21 April 2014
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