THE EARLY EMERGENCE OF COLD SENSATION IN SHAG NESTLINGS PHALACROCORAX-ARISTOTELIS

Neonate Shags Phalacrocorax aristotelis do not respond metabolically t o cold surroundings and depend completely for thermal protection on he at provided by the brooding parent. We examined whether neonate Shags have developed an ability to sense cold, even though a metabolic respo nse to cold surroundings is completely absent. Such information is imp ortant in order to identify the sequence by which the different mechan isms needed to maintain a stable body temperature are developed. Durin g cold exposure, 1-9 day old Shag nestlings were unable to produce hea t by physiological means and responded to body cooling by vocalization . Nestlings 12 days old were able to maintain a stable body temperatur e during cold exposure and did not call. These results strongly sugges t that neonate Shags have developed an ability to sense cold, which ca n trigger a behavioural thermoregulatory response well before they are capable of facultative thermogenesis. The lack of a metabolic cold re sponse may be due to either the immature state of the skeletal muscles , or to an underdevelopment of neuromuscular connections. Vocalization is probably mediated by dynamic activity of thermoreceptors, as the b ody temperature per se seems to be of minor importance in terms of con trolling the response. It is suggested that vocalization is mediated b y fast-acting cutaneous thermoreceptors.