Female begging calls reflect nutritional need of nestlings in the hen harrier Circus cyaneus

Steve Redpath,Alex Thompson,Arjun Amar

doi:10.1186/s12862-017-0986-z

Abstract

BackgroundMost birds exhibit bi-parental care with both sexes providing food for their young. Nestling signal food needs through begging. However, for some species, males rarely visit the nest, so have limited opportunity for gaining information directly from the chicks. Instead, females beg when males deliver food. We tested whether this calling signalled nutritional need and specifically the needs of the female (Breeder Need hypothesis) or that of their chicks (Offspring Need hypothesis).ResultsWe observed begging and provisioning rates at 42 nests of hen harrier (Circus cyaneus) in Scotland, explored the factors associated with variation in begging rate and the relationship between begging and provisioning. We also tested the impact of food on begging and provisioning through a feeding experiment. Female begging rate increased up to a chick age of 3 weeks and then tailed off. In addition, begging increased when broods were large.ConclusionsOur data provided support for the Offspring Need hypothesis. At nests where adlib food was provided females reduced their begging rate. These patterns suggested that female begging was an honest signal of need. However, begging continued even with adlib food and was only weakly associated with greater provisioning by males, suggesting that these calls may also play an additional role, possibly reflecting sexual or parent-offspring conflict.

Highlights

Most birds exhibit bi-parental care with both sexes providing food for their young
If the Offspring Need Hypothesis was true, we would expect the rate of begging to reflect growth rates and food intake needs of the chicks and to be lowest at hatching and greatest for middle nestling ages [26, 28, 29]. To test these hypotheses and explore patterns in female begging, we first confirmed the relationship between the food intake rate of chicks and nestling age; second, we examined how female begging varied in relation to the age of chicks and brood size; third, we examined the relationship between female begging rate and male provisioning to explore whether males can adjust their provisioning in relation to female begging
At the 28 unfed nests, female begging rate varied with chick age (F4,380 = 4.85, P < 0.001), and showed a similar pattern to the nutritional needs of chicks (Fig. 1b)

Summary

Introduction

Most birds exhibit bi-parental care with both sexes providing food for their young. Nestling signal food needs through begging. Breeding birds have to decide how much time to devote to foraging versus a range of other behaviours, such as protecting their young against adverse weather or predators These decisions are complicated when the two parents are foraging independently as each adult needs a way of assessing how hungry their chicks are. The female attends to the chicks and feeds them, whilst the male either drops prey on a perch nearby (eg goshawk Accipiter gentilis, peregrine Falco peregrinus, or sparrowhawk Accipiter nisus), or passes the food to the female in the air (eg harriers Circus spp.) The males of these species gain little direct information about chick condition on which to base their foraging decisions.

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Results

Discussion

Conclusion