Date of Award:

5-1-1991

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biology

Department name when degree awarded

Biology

Committee Chair(s)

Kimberly A. Sullivan

Committee

Kimberly A. Sullivan

Committee

James A. Gessaman

Committee

Thomas C. Edwards, Jr.

Abstract

Data presented in this thesis were collected on a population of Yellow-eyed Juncos (Junco phaeonotus) in the Chiricahua Mountains of southeastern Arizona, from 1985 to 1990. Severe drought and an associated reduction in the food supply occurred at the study site in 1989 and 1990. This provided the opportunity to document the effects of stressful environmental conditions on the breeding biology of the juncos. My field work covered the 1989 season, and for comparative purposes these thesis data are combined with data previously collected by Dr. Kimberly A. Sullivan and Dr. Wesley W. Weathers. Clutch size did not vary over the study years, although hatching success of eggs did decline significantly in 1987 and 1990. Brood size was significantly smaller in the second drought season. In the drought seasons, hatch lings were significantly lower in mass and the duration of the nestling period significantly increased. However, nestling growth, measured in terms of daily changes in mass, did not vary with season. The drought conditions did not influence parental effort. The field metabolic rates of adults provisioning nestlings were measured with the doubly labeled water technique. During the drought, parent juncos did not expend more energy than in the better years. In addition, the energy expenditure of adults provisioning nest lings did not vary with brood size, in either the favorable seasons or the drought season. Time allocated to foraging by parents feeding nest lings did not increase during the drought and did not vary with brood size. We conclude that Yellow-eyed Juncos do not adjust breeding effort to local conditions. In seasons with low food availability adults are still able to provision normal size broods.

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