Female birds monitor the activity of their mates while brooding nest-bound young

Abstract

In addition to food and protection, altricial young in many species are ectothermic and require that endothermic parents provide warmth to foster growth, yet only one parent-typically the female-broods these young to keep them warm. When this occurs, reduced provisioning by males obliges females to forage instead of providing warmth for offspring, favoring the temporal mapping of male activities. We assessed this in a wild house wren population while experimentally feeding nestlings to control offspring satiety. While brooding, females look out from the nest to inspect their surroundings, and we hypothesized that this helps to determine if their mate is nearby and likely to deliver food to the brood (males pass food to brooding females, which pass the food to nestlings). Females looked out from the nest less often when their partner was singing nearby and when his singing and provisioning were temporally linked, signaling his impending food delivery. Females also left to forage less often when their mate was nearby and likely to deliver food. Nestling begging did not affect these behaviors. Females looking out from the nest more often also provisioned at a higher rate and were more likely to divorce and find a new mate prior to nesting again within seasons, as expected if females switch mates when a male fails to meet expectations. Our results suggest anticipatory effects generated by male behavior and that brooding females temporally map male activity to inform decisions about whether to continue brooding or to leave the nest to forage.

Keywords: Classical conditioning; Cost of reproduction; Parental care; Parent–offspring conflict; Sexual conflict; Temporal mapping.

Fig. 1

A female house wren looking out from her nestbox while perched inside the entrance (photo credit: Dylan M. Poorboy, used with permission)

Fig. 2

(a) Relative frequency of latencies (min) between subsequent male behaviors (alternating singing and provisioning, successive provisioning trips, and successive songs), inset is the average time (min) elapsed between these behaviors, (b) frequency with which females looked out from the nest and (c) time spent brooding their young in relation to the time elapsed between a male’s song and his subsequent food delivery. Observations lasted for an hour immediately following nestling supplementation. Means ± SE are plotted in (a); regression lines in (b,c) depict the fitted predictions ± 95% CI from a generalized linear mixed model while accounting for the other factors (see Table 2), and inset with each are areas of overlapping data

Fig. 3

Probability of leaving the nest in relation to the time elapsed since the male last sang or delivered food. Darker areas indicate an increased probability of leaving to forage and lighter areas a reduced probability, as predicted from a generalized linear mixed model while accounting for the other factors (see Table 3)

Fig. 4

Probability of divorce, or the switching of mates before a subsequent nesting attempt, in relation to (a) the frequency with which females looked out from their nests and (b) delivered food to the nest during our observations. Regression lines depict the fitted predictions ± 95% CI from a generalized linear mixed model while accounting for the other factors (see Table 4); light and dark squares are individual observations in which the pair did or did not divorce, respectively