Date of Award:

5-1-1974

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Department name when degree awarded

Biology

Committee Chair(s)

Keith L. Dixon

Committee

Keith L. Dixon

Abstract

Cassin's Finch populations were studied in northern Utah during three breeding seasons and three winters to determine patterns of breeding, factors limiting breeding population size, social dominance and individual survival in winter flocks, and interrelationships of social systems between the seasons. Population levels on the breeding area, Beaver Mountain, Cache County, exhibited marked fluctuations from year to year; and males significantly outnumbered females in these populations. Cassin's Finches nested in colonies that varied in size from 9 to 20 nests. Adult males in reddish plumage predominated in breeding; but, if lost from the population or experimentally removed by shooting, they were replaced by yearling brown males that were both behaviorally and physiologically capable of breeding. Significant differences in testicular development between adult and yearling males in spring were not found. Flocks composed of entirely yearling males were observed in each of the three summers, and their numbers may approach 25% of the population. Based on banding data and non-replacement of females that disappeared, numbers of females appears to be the limiting factor in breeding colonies observed. Territorial behavior centers around the female and is interpreted as a mated-female distance. It does not limit total numbers of breeding pairs but does function to space nests temporally within a colony. Habitat similar to that used for nesting remained vacant near the colonies studied. Thus, habitat factors did not appear to limit colony size nor restrict colony location. Estimation of the duration of molt of the primaries by regression analysis suggests that females may require 62 to 72 days, red males 66 to 75 days, and brown males 70 to 77 days to complete the annual molt. Molt does not appear to overlap with breeding. Adult males and females and their young leave the breeding and molting area prior to yearling males in early fall. Winter flocks of finches studied in Cache Valley lacked organization or continuity from day to day, and numbers of finches varied greatly from winter to winter. Males outnumbered females in winter flocks, but females appeared dominant over males at winter feeders. This dominance may represent a behavioral adaptation to improve female survivorship during the non-breeding season since fewer females disappeared from winter flocks than did adult or yearling males.

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