Vocal traits of shorebird chicks are related to body mass and sex

Acoustic communication is critical during early life phases in precocial birds (e.g. adult alarm calls elicit antipredator responses in young; vocalisations of lost chicks help parents to find them). Chick vocalisations also may communicate information to parents about chick identity, condition, sex, or age. We investigated whether chick calls of two species of Australian Charadriidae vary with sex or body mass. During studies of Red-capped Plover Charadrius ruficapillus and Southern Masked Lapwing Vanellus miles novaehollandiae, we handled chicks for purposes of measurement, sampling blood, and banding. We opportunistically recorded their “distress calls” while in the hand, and analysed the calls to determine whether call structure is related to sex or body mass (a proxy for age). We measured five structural traits per call plus time intervals between successive calls for 26 plover chicks (2600 calls) and 95 lapwing chicks (6835 calls). In plovers, inter-call intervals were shorter in males and both inter-call interval and the frequency range of calls decreased with increasing body mass. In lapwings, frequency modulation (computed as the range in the rate of change of the dominant frequency) was lower in male calls. The frequency range of lapwing calls decreased with mass in both sexes, but the decline was greater in males, resulting in a lower frequency range in that sex. Frequency modulation and entropy of lapwing calls also decreased with increasing body mass. Minimum frequency did not change with body mass or sex in either species. Our study provides the first evidence for charadriid chicks of (a) a sexual difference in call structure or rate and (b) gradual growth-related changes in call structure and rate, across chicks. Studies on a broader range of chick calls and species within this large and diverse family would be valuable. We provide a foundation for further studies of shorebird vocalisations during growth, which may underpin additional studies exploring the development and functional significance of such vocalisations.