Parental behavior exhibits among-individual variance, plasticity and heterogeneous residual variance

Phenotypic variance should have a hierarchical structure because differences arise between species, between individuals within species, and, for labile phenotypes, also within individuals across circumstances. Within-individual variance could exist because of responses to variable environments (plasticity) or because exhibiting variance per se has fitness consequences. To evolve, the latter requires between-individual variance in within-individual variance. Here, we investigate the parental behavior of female red-winged blackbirds (Agelaius phoeniceus) and assess if the distribution of within-individual variance also differs between individuals or changes with respect to environmental conditions. We used a statistical approach that models both the mean and variance iteratively. We found that the amount of food delivered per second on each visit was influenced by female identity, nestling age, and the location (on vs. off territory) where the female foraged. Moreover, we also found that ...