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.<br>

早成鸟（precocial birds）的早期生命阶段中，声学通讯至关重要：例如成鸟的警戒鸣叫声可引发雏鸟的反捕食应答，走失雏鸟的鸣叫声可帮助亲鸟定位其位置。雏鸟鸣叫声还可向亲鸟传递个体身份、身体状况、性别或年龄等信息。
本研究旨在探究两种澳大利亚鸻科（Charadriidae）鸟类的雏鸟鸣叫声是否随性别或体质量发生变化。
研究对象为红顶鸻（Charadrius ruficapillus）与南方蒙面麦鸡（Vanellus miles novaehollandiae）的雏鸟，研究过程中我们对雏鸟开展了体质量测量、采血及环志操作，并借此机会录制了它们在人类握持状态下发出的“遇险鸣叫声”，随后对这些鸣叫声进行分析，以判断鸣叫声结构是否与性别或体质量（作为年龄的替代指标）相关。
我们共为26只红顶鸻雏鸟（共计2600条鸣叫声）与95只南方蒙面麦鸡雏鸟（共计6835条鸣叫声）的每条鸣叫声测量了5项结构特征，并统计了连续鸣叫声之间的时间间隔。
结果显示：在红顶鸻雏鸟中，雄性个体的鸣叫声间隔更短，且鸣叫声间隔与鸣叫声频宽均随体质量增加而降低；在南方蒙面麦鸡雏鸟中，雄性鸣叫声的频率调制（frequency modulation）更低，其鸣叫声频宽随体质量增加而降低，且该降幅在雄性个体中更为显著，最终导致雄性鸣叫声的频宽低于雌性。此外，南方蒙面麦鸡雏鸟鸣叫声的频率调制与熵（entropy）也随体质量增加而降低。两种鸟类雏鸟的最低鸣叫声频率均未随体质量或性别发生显著变化。
本研究首次为鸻科鸟类雏鸟提供了两方面证据：（1）鸣叫声结构或鸣叫声速率存在性别差异；（2）雏鸟鸣叫声结构与鸣叫声速率随生长进程发生渐进性变化。针对该大类群下更多物种与更多雏鸟鸣叫声的研究将具有重要科学价值。本研究为滨鸟生长过程中的鸣叫声相关研究奠定了基础，可为后续探究此类鸣叫声的发育过程与功能意义提供支撑。