Variance partitioning of nest provisioning rates in blue tits: individual repeatability, heritability, and partner...

In many animal species, including most birds, parental care is performed by both parents, which has important implications for mate choice (good parent hypothesis) and parental investment strategies. Partitioning the variance in measures of parental care into heritable and nonheritable components is important to understand the evolvability of parental investment and its potential role in mate choice. We employed an automated system to monitor provisioning behavior at 817 blue tit nests over 10 years (totaling ~3 million visits). Daily provisioning rates of males and females were moderately repeatable between years (Radj = 0.16 and 0.15, respectively), which was almost entirely explained by additive genetic effects. While this degree of heritability is sufficient for parental investment to respond to selection, we argue that the modest level of repeatability provides limited potential for a "provisioning phenotype" to be used as a criterion in mate choice. Daily visit rates were positively correlated between pair members, but after accounting for shared environmental factors, this relationship became clearly negative, thereby providing support for models of partial compensation. Visit rates also differed substantially between years, and between days within a year. Thus, it is important to account for these variables when comparing the parental investment between individuals. Our results highlight the interplay between genetic, social, and environmental influences on provisioning behavior.