Data from: Acoustic cues from within the egg do not heighten depredation risk to shorebird clutches

Egg predators use an array of olfactory and visual cues to locate eggs. Precocial avian embryos within eggs can produce vocalizations for a period prior to hatching, which may be audible to predators. Here, we investigated, under field conditions, the embryonic vocalizations emitted from eggs of a shorebird species, the Red-capped Plover Charadrius ruficapillus. We characterize the acoustic properties of the vocalizations and the circumstances under which they are emitted, then test whether such vocalizations are used as an acoustic cue by predators to locate eggs. Embryonic vocalizations typically occurred between 0 and 5 days before hatching (henceforth the “vocalization period”). Within the vocalization period, the maximum acoustic frequency (kHz) of vocalizations increased with egg age (perhaps as a consequence of embryonic development) and the minimum acoustic frequency (kHz) increased with ground temperature (perhaps as mode of communication with parents regarding thermal needs). An artificial nest experiment compared the survival of nests with and without acoustic cues (prerecorded embryonic vocalizations played continuously from the nest). Corvids were the major egg predator (accounting for 76% of cases of artificial nest predation). However, the presence of vocalizations did not affect the time taken for predators to locate and depredate eggs. Our results suggest that embryonic vocalizations are important signals that may aid in communication with parents but that they do not increase predation rates. Further research involving a greater diversity of predators (e.g., acoustic predators) is required to examine whether vocalizations from the egg incur costs under other predator regimes.卵捕食者依托一系列嗅觉与视觉线索定位鸟卵。早成鸟胚胎在孵化前的一段时期内可发出鸣叫声，此类鸣叫声有可能被捕食者感知。本研究于野外条件下，针对鸻形目鸟类红顶鸻（Red-capped Plover, Charadrius ruficapillus）的卵所产生的胚胎鸣叫声展开调查。我们对该鸣叫声的声学特性及其发出场景进行了表征，并检验捕食者是否会利用此类鸣叫声作为声学线索来定位鸟卵。胚胎鸣叫声通常出现在孵化前0至5天（下称"鸣唱期"）。在鸣唱期内，鸣叫声的最高声学频率（kHz）随卵的发育时长升高（推测与胚胎发育相关），而最低声学频率（kHz）则随地面温度上升而升高（可能是胚胎向亲鸟传递热需求的通讯方式）。本研究通过人工巢实验，对比了添加声学线索（从巢中持续播放预先录制的胚胎鸣叫声）与未添加声学线索的鸟巢的存活率。鸦科鸟类为主要的卵捕食者，占人工巢被捕食事件的76%。但鸣叫声的存在并未影响捕食者定位并取食鸟卵所需的时长。本研究结果表明，胚胎鸣叫声是一类重要的信号，可辅助胚胎与亲鸟进行通讯，但并不会提升卵的被捕食风险。未来还需开展涵盖更多捕食者类群（如声学捕食者）的研究，以探究卵内鸣叫声在其他捕食者群落中是否会带来被捕食的代价。