Adult mortality probability and nest predation rates explain parental effort in warming eggs with consequences for embryonic development time

Parental behavior and effort vary extensively among species. Life history theory suggests that age-specific mortality could cause this interspecific variation, but past tests have focused on fecundity as the measure of parental effort. Fecundity can cause costs of reproduction that confuse whether mortality is the cause or consequence of parental effort. We focus on a trait, parental time and effort in warming embryos, which varies widely among species of diverse taxa and is not tied to fecundity. We conducted studies on songbirds of four continents and show that time spent warming eggs varies widely among species and latitudes, and is not correlated with clutch size. Adult and offspring (nest) mortality explained most of the interspecific variation in time and effort that parents spend warming eggs measured by average egg temperatures. Parental effort in warming eggs is important because embryonic temperature can influence embryonic development period and, hence,
exposure time t...