Weather matters: begging calls are temperature- and size-dependent signals of offspring state

Begging calls provide a way for parents to gauge offspring state. Although temperature is known to affect call production, previous studies have not examined the influence of ambient temperature at the nest. We recorded ambient temperature and begging calls of 3 day-old tree swallows (Tachycineta bicolor). Our results indicate that typical daily temperature flux can dramatically alter a brood’s begging calls, depending on body size. Broods with small (low body mass) nestlings decreased the rate and length of their calls at colder temperatures, consistent with a biophysical constraint. In contrast, broods with large (high body mass) nestlings increased the rate of their calls at colder temperatures. Parents responded in a context-dependent manner, returning more rapidly after smaller nestlings gave longer begging calls. Our results suggest that the function of offspring begging calls is highly dynamic, with environmental conditions altering the relationship between begging calls and offspring state.