Date of Award:

5-1-1970

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Department name when degree awarded

Zoology

Committee Chair(s)

Keith L. Dixon

Committee

Keith L. Dixon

Abstract

Populations of color- marked mountain and black-capped chicakdees were studied at Beaver Mountain Ski Area, Cache County, Utah, an area of year-around sympatry. Aggressive interactions at winter feeding stations were quite frequent, with black-capped chickadees usually dominant over mountain chickadees. However, since mountain chicakdees won a substantial number of contests, an analysis of several factors possibly responsible for these reversals was made. The ones that had the greatest effect were sex of the participants, site of encounters in relation to black-cap winter ranges, and individual differences in birds. Other factors that seemed to have an effect, but less certainly so, were the absence of a male flock-mate at the time of encounters involving female black-capped chicakdees, and previous interspecific experience in combination with length of time on the area. Interspecific response to sound signals was absent in aggressive encounters, and visual displays were also unimportant in this respect. Other behavioral relationships in winter were also considered. Interspecific association away from feeding stations was infrequent, and mixed winter flocks were not formed. Blackcapped chickadee winter flock ranges overlapped mountain chickadee winter flock ranges. During the breeding season there was little behavioral interaction between members of the two species. Interspecific territoriality did not occur and interspecific response to sound signals was rare. Black-capped chickadee breeding territories and winter flock ranges occupied extensive aspen stands, whereas mountain chickadees tended more to utilize areas of coniferous or mixed forest. Thus, in spite of overlap of breeding territories and winter flock ranges, these two species probably avoid ecological competition. Apparently the two species have evolved in isolation for so long that their social behavior patterns have diverged enough that there is little carryover across specific boundaries. Also, it appears that evolution in isolation has resulted in the development of habitat preferences different enough that ecological competition is probably only slight in this area of sympatry.

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