Plumage brightness as an indicator of parental care in northern cardinals

Good parent and differential allocation models predict relationships between degree of sexual ornamentation and parental care, but relatively few studies have tested these models. The northern cardinal, Cardinalis cardinalis, is a sexually dichromatic species in which both sexes are ornamented. Males have red plumage, and females have tan plumage with limited areas of red feathering. Cardinals were used to address the two models and determine whether plumage brightness signals level of parental care by both sexes. Absolute effort in feeding nestlings by males was not correlated with male breast plumage colour, but effort by females was positively correlated with female underwing plumage colour. Absolute feeding effort by females was also inversely related to brightness of the mate's breast colour. As a consequence, the proportion of a pair's total feedings provided by the male was positively correlated with male breast colour. Proportion of total feedings provided by the female was positively correlated with female wing colour. Feeding efforts (both per nest and per nestling) were correlated between mates, but birds did not mate assortatively in relation to colour. These results support the good parent hypothesis, suggesting colour brightness is a signal of parental care. The results also indicate that ornamentation of both members of the pair may be important determinants of relative efforts in provisioning nestlings by parent birds. Copyright 1998 The Association for the Study of Animal Behaviour.