Relative Growth, Body Constituents, and Energy Content of Nestling Barn Swallows and Red-Winged Blackbirds

Abstract

growth as determined by this technique appears to vary throughout development, and tends to be greater than the caloric value of individual passerine nestlings reported in the literature. Future laboratory investigations of the energetics of nestling development from hatching to fledging might well consider aspects of metabolized energy as well as standard metabolism and caloric content of the nestlings. I am grateful to S. Charles Kendeigh and Herbert W. Kale II for critically reviewing this manuscript. LITERATURE CITED B^LDWIN, S. P., ^ND S.C. K•NDmOm 1932. Physiology of the temperature of birds. Sci. Publ. Cleveland Mus. Nat. Hist. 3: 1-196. Breeding attempts by juvenile Great Blue Herons.-Although most North American herons probably do not attempt to breed for the first time until the breeding season of their second year, records of breeding by Black-crowned Night Herons (Nycticorax nycticorax) (Gross 1923), Green Herons (Butorides virescens) (Meyerdecks, in Palmer 1962), and Little Blue Herons (Florida caerulea) (Palmer 1962) in juvenal plumage indicate that in these species a few individuals attempt breeding at about 1 year of age. Owen (1959) reported breeding that he considered exceptional by yearling Grey Herons (Ardea cinerea) in Great Britain. Millstein et al. (1970) found breeding attempts by yearling Grey Herons to be common at