Abstract
INVESTIGATIONS of seasonal changes in thyroid histology in wild birds have shown that increases in activity occur in the period preceding and during the annual molt (Davis and Davis, 1954; Assenmacher, 1958; Voitkevich, 1966) and in response to low temperature (Wilson and Farner, 1960; Kendeigh and Wallin, 1966). Involvement of the avian thyroid in migration and reproduction has also been suggested (Hohn, 1961). Although Phillips and van Tienhoven (1962) collated changes in thyroid activity with events within the breeding season in female Pintails (Anas acuta), information of this type is not available for other species. Few studies have considered sex differences in thyroid metabolism. This paper reports observations of seasonal variations in thyroid histology in a nonmigratory population of Black-billed Magpies (Pica pica hudsonia) near Laramie, Wyoming. Special attention was accorded (1) changes in thyroid activity in connection with major events in the breeding season, and (2) differences in thyroid dynamics as related to sex and age.
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