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

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Abstract
Changes in behavior, body weight, gonad size, molt and subcutaneous fat in Zonotrichia leucophrys gambelii were studied at lat. 64[degree]49'' N. in the post-breeding period in 1957. In an area approximately 0.3 mile in diameter, 346 birds were trapped between June 26 and Aug. 27. Of these, 254 were banded and released, and 92 were kept for specimens. Territory defense had declined by June 30, flocks formed by July 9, migratory behavior was 1st seen on Aug. 7, and the 1st temporary decline in numbers began Aug. 9. By Aug. 30 all Gambel''s sparrows had left the trapping area. Analysis of the molt and fat accumulation stages in dissected specimens and observations of molt on live birds indicate that Gambel''s sparrows may begin migration while still molting and before they accumulate much fat. Nesting birds banded in May and June were never recaptured after July 21. Fluctuations in numbers preceded by 3 1/2 weeks a steady decline in numbers. Percentages of unhanded birds trapped per day remained high to the end of the study. Intervals between 1st and last capture of banded individuals averaged only 9.8 days for 6 adults and only 7.7 days for 22 birds trapped as juvenals. These facts indicate that a series of influxes and departures of groups of Gambel''s sparrows took place in late summer, with no substantial numbers of local breeding birds remaining at the trap sites after mid-July. Therefore, variations in samples of Gambel''s sparrows taken from a given locality in late summer may be due to interpopulational as well as individual differences.