EMBRYONIC CALLS AS CARE-SOLICITING SIGNALS IN BUDGERIGARS, MELOPSITTACUS-UNDULATUS

Embryonic calls occur 1-3 d before hatching among precocial and some a ltricial birds. In precocial species, rails may synchronize hatching a mong siblings or, in semi-precocial species, elicit parental attention to, and often thermoregulation of, the hatching egg. Much less is kno wn about the functional significance of calls in fully altricial speci es. In this study, naturalistic observations and laboratory experiment s were used to document factors affecting calling and the parental res ponses to calls in one altricial species, the budgerigar Melopsittacus undulatus. Budgerigar chicks hatch asynchronously and vocalize 24-48 h before hatching. Embryonic calling rates increase at higher egg temp eratures, and also as embryos near hatching. Parents easily locate a c alling egg in their clutch, even among a large brood of much older, vo calizing nestlings. Furthermore, they actively assist in the last stag es of hatching by helping to break the shell along the crack in the eg g. Both observational and experimental evidence suggests that embryoni c vocalizations are distinctive signals that increase parental attenti on and care, and may stimulate hatching assistance to a calling egg.