The effects of rainfall on different components of seasonal fecundity in a tropical forest passerine

Abstract

Seasonal fecundity is a composite metric that is determined by component parameters such as clutch size, nest survival and re-nesting probability. Many of these component parameters are known to vary with environmental conditions, in particular rainfall prior to or during the breeding season. In some species, seasonal fecundity is positively related to rainfall, but little is known about which component parameters of seasonal fecundity respond most strongly to rainfall. We used intensive nest monitoring of a multi-brooded tropical forest passerine, the Montserrat Oriole Icterus oberi, to examine the effects of rainfall during the pre-breeding season on component parameters of annual fecundity. We monitored all nests of a total of 42 pairs over 5 years in which rainfall varied substantially. We then related clutch size, nest survival, onset and length of the breeding season, re-nesting probability and re-nesting interval to pre-breeding season rainfall using generalized linear mixed models that accounted for random variation across sites and individual pairs, and incorporated other variables known to affect the response. Higher pre-breeding season rainfall led to an increase in clutch size and a decrease in re-nesting interval, but nest survival, re-nesting probability and length of the breeding season were not affected by variation in rainfall. The onset of the breeding season was delayed in very dry years. We conclude that higher rainfall is likely to increase food availability and thus body condition of female Montserrat Orioles, leading to an increase in fecundity due to larger clutch sizes.