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 vocalisations for a period prior to hatching, which may be audible to predators. Here we investigated, under field conditions, the embryonic vocalisations emitted from eggs of a shorebird species, the red-capped plover Charadrius ruficapillus. We characterise the acoustic properties of the vocalisations and the circumstances under which they are emitted, then test whether such vocalisations are used as an acoustic cue by predators to locate eggs. Embryonic vocalisations typically occurred between 0 and 5 days before hatching (henceforth the “vocalisation period”). Within the vocalisation period, the maximum acoustic frequency (kHz) of vocalisations 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 (pre-recorded embryonic vocalisations played continuously from the nest). Corvids were the major egg predator (accounting for 76% of cases of artificial nest predation). However, the presence of vocalisations did not affect the time taken for predators to locate and depredate eggs. Our results suggest that embryonic vocalisations 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) are required to examine whether vocalisations from the egg incur costs under other predator regimes.

卵捕食者会利用一系列嗅觉与视觉线索来定位鸟卵。处于卵内的早成鸟胚胎（precocial avian embryos）可在破壳前的一段时间内发出鸣叫声，此类鸣叫声有可能被捕食者所听见。本研究在野外条件下，针对一种滨鸟——红顶鸻（Charadrius ruficapillus）的卵所发出的胚胎鸣叫声展开了调查。我们首先对这类鸣叫声的声学特性及其发出的情境进行了表征，随后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破壳前0至5天（下称"鸣唱期"）。在鸣唱期内，鸣叫声的最高声学频率（千赫兹，kHz）随卵的日龄增长而升高（这或许是胚胎发育所致），而最低声学频率（kHz）则随地面温度升高而上升（这可能是胚胎与亲鸟交流热需求的一种方式）。

我们开展了人工巢实验，对比了有声学线索（从巢中持续播放预先录制的胚胎鸣叫声）与无声学线索的鸟巢的存活率。鸦科鸟类为主要的卵捕食者（占人工巢被盗食案例的76%）。但鸣叫声的存在并未影响捕食者定位并盗食鸟卵所需的时长。

本研究结果表明，胚胎鸣叫声是一类重要的信号，或可辅助胚胎与亲鸟进行交流，但并不会提高卵被捕食的概率。未来还需开展涵盖更多类群捕食者（例如依赖声学线索的捕食者）的研究，以探究卵内胚胎鸣叫声在其他捕食者群落中是否会带来被捕食的代价。