Biology of White-Crowned Sparrows in Late Summer at College, Alaska

Abstract

This paper reports on the results of observing, banding, and collecting Gambel's White-crowned Sparrows (Zonotrichia leucophrys gambelii) at College, Alaska, near Fairbanks (lat 64049' N) in late summer of 1957. For ease of communication, this race will be called Gambel's Sparrow hereafter in this report. Its behavior and physiological concomitants have been studied extensively on the wintering grounds from September through April and on the breeding grounds from arrival of the males in early May through fledging of the young in mid-June (Michener and Michener, 1943; Blanchard and Erickson, 1949; Oakeson, 1954; Wilson and Farner, 1960; and King and Farner, 1963). Less is known of the behavior of Z. 1. gambelii from late June through August. The work presented here concerns behavior and physiological concomitants in Gambel's Sparrows at College from late June through 30 August 1957. King, Farner, and Morton (1965) analyzed body weight and lipid reserves and King, Follett, Farner, and Morton (1966) studied gonad cycles in Gambel's Sparrows collected near Fairbanks in late summer of 1962 and in May and June of 1963. Although their aims and methods were different from mine, our data are complementary in several respects. This work was undertaken in connection with analysis of seasonal changes in thyroid histology in this race (Oakeson and Lilley, 1960). I wanted to know whether specimens collected near Fairbanks in July and August represented only local breeding birds and their offspring or whether my samples included individuals that moved into the area after nesting was over. If my samples included transients, I wanted to find out how long they lingered, when local breeding birds stopped entering traps, and what was the date of the earliest sign of fall migration. Since individual birds may move about while the number of birds foraging in a given area stays approximately the same, the only way to discover whether I was sampling a stable or shifting population was to band large numbers of individuals in a restricted area and retrap there frequently. From observations by T. T. McCabe, reported in Blanchard and Erickson (1949), we know that in British' Columbia Gambel's Sparrows with young still begging for food may move at least 40 or 50 miles away from breeding grounds by early July. Early storms in the mountainous breeding grounds of British Columbia might provide the stimulus for such movement. In the lowland nesting grounds of central Alaska, on the contrary, the climate of late summer is reliably warm, and the forage is excellent at least until early September. Is there evidence of movements of Gambel's Sparrows in July there also? I hoped to throw light on this question by concentrating banding operations in a cultivated field where I had watched Gambel's Sparrows during nesting. I knew the number of pairs whose territories included parts of this field, and the range of clutch sizes. I could, therefore, estimate the theoretical maximum number of local Gambel's Sparrows that might forage in this field before movement away from or into the area took place. This estimate constituted a basis of comparison for subsequent observations of numbers at this place.