Prolactin and helping behaviour in the cooperatively breeding Florida scrub-jay, Aphelocoma c-coerulescens

The relationship between parental and alloparental behaviours and prolactin was examined by measuring plasma levels of prolactin in cooperatively breeding Florida scrub-jays during three breeding seasons. The seasonal trends were similar to those in several other avian species, with low prolactin titres during the pre-nesting phase that steadily increased to a maximum during the incubation and nestling periods. Females had higher prolactin levels than males, and breeders had higher levels than non-breeders. Circulating prolactin in non-breeders was elevated prior to the time when they were exposed to a nest or young, suggesting that high prolactin levels were not a simple response to the stimulus of begging young. To further assess correlations between prolactin and parent-like behaviours, the number of nest visits and the amount of food delivered to focal nests was monitored. Prolactin levels were significantly correlated with the number of visits to the nest, as well as the amount of food delivered to the young. Non-breeders that fed nestlings had higher prolactin titres than non-breeders that did not help, lending further support to the hypothesis that helping behaviours are mediated by prolactin. (C) 1996 The Association for the Study of Animal Behaviour