Song and Territory Defense in the Red-winged Blackhird

(Ricklefs 1973). The Black Vultures' growth rates (0.079 and 0.068) are 20-30% lower than Ricklefs' (1973) expected value for altricial and semi-altricial land birds of comparable adult weight. The slow growth of Black Vultures may be related to precocity of development compared to faster growing raptorial birds (see Ricklefs 1973); the nestlings' dense down may indicate early development of homeothermy. Alternatively, slow growth may be related to the nutrient content of their food, i.e. the extent to which fruits or other plant material comprise their (presumably) mostly carrion diet. In addition, there may be energy limitations imposed by their dependence on carrion for food. Carrion may be an unpredictable resource in time and space, due to both the variability of its occurrence and to conditions limiting foraging activity. Hatch (1970) observed Turkey Vultures remaining on their roosts for 2 days in rainy weather, while Stewart (1974) observed that Black Vulture young that were normally fed several times daily were not fed on a rainy day. The reduced growth rates of Black Vulture young may be adaptive in ameliorating the "feast or famine" nature of scavenging. I thank D. Janos for photographing nestlings, E. Willis, I. L. Brisbin, and R. E. Ricklefs for commenting on the manuscript, and the Smithsonian Tropical Research Institute for logistic support. Special thanks are due G. C. White and I. L. Brisbin for the growth parameter analysis and interpretation.