Growth Rate and Development of Endothermy in the Snow Bunting (Plectrophenax Nivalis) and Lapland Longspur (Calcarius Lapponicus) at Barrow, Alaska

Abstract

The growth rate, general development, and the development of endothermy of two closely related passerines–the snow bunting (Plectrophenax nivalis) and the Lapland longspur (Calcarius lapponicus)–were studied near Barrow, Alaska. Although there is a 30% difference in adult weight of the two species, comparison of their daily weight curves and of the development of their plumage and behavior indicate essentially identical developmental rates. The rate and pattern of the development of endothermy support this conclusion. Both species are ectothermic at hatching, and both are essentially endothermic by the seventh day of life. The two species fledge at different ages, 7.4 days for the longspur and 13.1 days for the snow bunting. Fledging is thus shown to be a behavioral trait independent of development. The difference between the two species is correlated with different nesting ecologies: the longspur nests in open—cup nests, and the bunting nests in cavities. These results are compared with several other fringillids of the same subfamily (Emberizinae). The developmental rates of all are found to be very similar. There is no difference between arctic nesting and temperate nesting forms. The postulate that arctic passerine birds grow more rapidly than related temperate forms is not supported by any existing evidence.