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.