Vocal Response of Eared Grebe Embryos to Egg Cooling and Egg Turning

Abstract

In a laboratory study, the vocal responses of Eared Grebe (Podiceps nigricollis) embryos to egg cooling and egg turning were examined. Nineteen late-stage, prepipping embryos were twice subjected to 10 min of egg cooling and 10 min of normal incubation temperatures. Experimentally cooled embryos vocalized more than embryos exposed to normal incubation temperatures. Cooled embryos produced more bouts of calls and fewer calls per bout than when exposed to normal incubation temperatures. Intercall intervals within bouts did not differ between warm and cold periods. Results of the egg-cooling experiment support the "care-soliciting signal" hypothesis. In a separate paired experiment, embryos vocalized more when turned than when at rest. Because grebe nests are composed of sodden materials, embryos that are about to hatch may signal their parents to turn the eggs, because positioning a pipped egg upside down may suffocate the embryo. Also, prepipped embryos may vocalize more frequently when turned as a signal to their parents that they are viable and will soon hatch. Eared Grebe embryonic vocalizations probably are multifunctional, with care-soliciting being one of their functions.