Growth and Energy Requirements of Hand-Reared Great Blue Heron (Ardea herodias) Chicks

Abstract

The energy requirements of 12 hand-reared Great Blue Heron (Ardea herodias) chicks were determined using a continuous feeding trial. Male (n = 8) and female (n = 4) chicks did not differ in their hatching mass, but by day 30 the mass of male chicks was significantly greater than the mass of female chicks. At fledging, male chicks (x = 2,465 + SE of 51 g) were about 13% heavier than female chicks (2, 179 ? 10 g). The growth rate of male chicks (logistic growth rate (k) of 0.167 ? 0.004/day and absolute growth rate (AGR) of 70.7 ? 4.1 g/day) was significantly different from the growth rate of female chicks (k of 0.178 ? 0.003 /day, and AGR of 60.5 ? 0.4 g/day). Metabolizable energy intake (ElME) and energy requirements did not differ between male and female chicks. El,, was maximal between days 26 and 41 at 2,027 ? 25 kJ/day. The total energy requirement for gain (kJ/day) was greatest between 10 and 29 days of age, the time of maximum growth. The total energy requirement for maintenance (kJ/day) was greatest between 30 and 39 days of age. Our study provides evidence to support the hypothesis that reproductive success of Great Blue Herons is limited by the parents' ability to gather food. Brood size at fledging predicted by the relationship between parental effort and the chicks' energy requirements is similar to the observed number of young fledged per successful nest. Peak mortality of wild nestlings occurs during the time of peak chick energy requirements as indicated by our study. Received 7 June 1993, accepted