Metabolic costs and honest signalling of need during the development of endothermy in American white pelicans

Abstract

I examined the development of endothermy in American white pelican chicks (Pelecanus erythrorhynchos) during the first 16 days after hatching. My results suggest that, while pelican chicks reached a modest degree of incipient endothermy by day 7, thermoregulatory self-sufficiency was not well developed until day 16. The age of endothermy in pelicans was similar to those reported for other large pelecaniform species studied to date. Honest signalling models predict that if offspring solicitation is a true reflection of need, then solicitation should be costly and costs should increase with need. I measured the metabolic costs of vocal heat solicitation calls given by pelican chic s in response to anticipated thermal need on days 1, 4, 7, 10 and 13. Call rates, metabolic rates (Vo$\sb2$) and body temperatures were measured during exposure to both warm (mid-thermoneutral) and cold (5$\sp\circ$C below thermoneutral) ambient temperatures. I also measured the call rates, Vo$\sb2$ and body temperatures of pelican chicks (days 1, 4, 7, 10 and 13) exposed to warm (mid-thermoneutral) and cold (5$\sp\circ$C below thermoneutral) ambient temperatures, and those given the opportunity to vocally thermoregulate. (Abstract shortened by UMI.)