Male parental investment reflects the level of partner contributions and brood value in tree swallows

Abstract

Biparental care presents an interesting case of cooperation and conflict between unrelated individuals. Several models have been proposed to explain how parents should respond to changes in each other’s parental care to maximize their own fitness, predicting no change, partial compensation, or matching effort as a response. Here, we present an experiment in tree swallows (Tachycineta bicolor) in which we increased the offspring provisioning of females by presenting them, but not their mates, with additional nestling begging calls using automated playbacks. We performed this experiment in two populations differing in future breeding opportunities. We found that in response to a temporary increase in female parental effort, males in the northern population (with lower future breeding opportunities and thus higher brood value) matched the increased effort, whereas males in the southern population did not. We also found that increases in parental care during playbacks were driven by the females (i.e., females initiated the increased effort and their mates followed them) in the northern population but not the southern population. These results support the idea that with incomplete information about the brood value and need, cues or signals from the partner might become important in coordinating parental care.

Significance statement

Male tree swallows increase parental effort when their mates need to work harder. Using an automated system, we broadcast playback of hungry nestling calls only when the female parent was visiting the nest. In a population where the value of the current brood was high, males significantly increased their provisioning rate, much more than their partners did. Since only the females could hear the playbacks, and the begging of the nestlings did not change in response to the treatment, we suggest that either the males used their partner’s feeding rate as a cue or the females may have communicated to their mates that they should work harder. These results suggest that cues or signals from the partner may be important in coordinating parental care.