Embryonic vocalisations mediate parental care in Masked Lapwings (Vanellus miles) but not Red-capped Plovers (Charadrius ruficapillus)

Embryonic vocalisations in birds may
enable communication between embryos and incubating parents but responses of
parents to embryonic vocalisations have not been measured experimentally. In
two ground-nesting shorebirds, we compare parental care of eggs without embryonic
vocalisations, those with natural embryonic vocalisations, and those in which
we experimentally introduced embryonic vocalisations, while accounting for prevailing
temperatures. We continuously recorded nests (one block of up to 24 hours per
nest) of two ground-nesting shorebirds, the Red-capped Plover Charadrius
ruficapillus and Masked Lapwing Vanellus miles and quantified parental
behaviours. We predict an increase in egg thermoregulation behaviours (time
spent incubating or shading) and ‘fussing’ (a combination of rising and re-settling,
shuffling, orientation change and egg turning), when vocalisations were naturally
present or when they were experimentally introduced in comparison to when no
vocalisations were present (control). In lapwings, the rate of fussing
increased at the nest only when natural vocalisations were present, however,
preening increased when natural or introduced vocalisations were present.
Additionally, the frequency of bill to egg touches (inspections) increased only
in the presence of introduced vocalisations. For plovers, treatment had no
influence on parental behavioural, however, the frequency of fussing, bill to
egg touches, and shell tossing increased with air temperature. For both
species, there was no influence of the presence of embryo’s vocalisations
(natural or introduced) on the parent’s egg thermoregulation behaviours. Our
results highlight that acoustic communication across the eggshell may occur and
can influence parental care in shorebirds but appears to be species-specific.