The functions of adult female begging during incubation in sub-Arctic breeding yellow warblers

Begging behaviour in birds is frequently studied in nestlings, but the function of adult female begging behaviour remains unknown. We examined begging behaviours of adult female yellow warblers, Setophaga petechia, during incubation at the northern limit of their breeding range. Female yellow warblers beg only when their mate arrives at the nest, and vocalization duration, intensity of wing fluttering and position of the femaleʹs body on the nest varies between begging events. We measured changes in these characteristics for 696 begging events from nine incubating females and examined how begging intensity changed with temperature and time since a femaleʹs last feeding. Begging intensity increased as the duration between feedings increased especially during colder temperatures. Next, we investigated how male feeding rates changed in response to variation in female begging intensity. Males fed females more quickly in response to intense begging during warm temperatures but not during cold temperatures. Finally, we investigated whether male feeding rates influenced the frequency or duration of the femaleʹs bouts away from the nest (i.e. ‘off-bouts’) during which the female had the opportunity to forage. Females that were fed more frequently reduced the average duration, but not the frequency, of their off-bouts. These results suggest that variation in the intensity of female begging behaviour signals energetic need, and that begging during incubation may be an important adaptation allowing female yellow warblers to maximize incubation time when breeding in sub-Arctic environments.