Nest attentiveness and egg temperature do not explain the variation in incubation periods in tropical birds

Abstract

Summary The wide range in incubation periods among bird species has puzzled biologists for decades, because an extended egg‐phase increases time‐dependent mortality of the eggs. We investigated a recently proposed mechanistic explanation inspired by life‐history theory, suggesting that adults may increase their own survival by reducing nest attentiveness, the percentage of daytime spent incubating eggs, in exchange for reduced offspring (egg) survival due to a longer incubation period. Incubation behaviour and egg temperatures (Tegg) of 14 bird species in the humid lowland tropics were studied to test the hypothesis that lower nest attentiveness and reduced Tegg cause longer incubation periods. Increased nest attentiveness correlated with higher average Tegg. However, neither nest attentiveness nor average Tegg was associated with the length of the incubation period. Longer off‐bouts resulted in lower Tegg, but neither number of off‐bouts nor off‐bout length was associated with incubation period. In addition, we reanalysed a previously published negative association between Tegg and incubation period based on literature data from temperate passerine birds using a larger data set and found no significant correlation. In conclusion, our results do not support the hypothesis that longer incubation periods are caused by reduced nest attentiveness and corresponding lower Tegg.