Date of Award:

5-1-1997

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biology

Committee Chair(s)

Kimberly A. Sullivan

Committee

Kimberly A. Sullivan

Committee

Mark E. Ritchie

Committee

Edward W. Evans

Abstract

Individuals and populations are likely to optimize methods of food harvest and synchronize reproduction with local peaks in food supply, because animals exhibiting greater efficiency at acquiring energy or energy intensive tasks will often achieve greater survival, growth, and reproduction. Although this statement implies that foraging efficiency is optimized by selection for better foragers and optimal foraging theory owes much of its development and refinement to studies of free-living birds, the positive association of foraging proficiency and fitness has not been documented for free-ranging birds. Furthermore, the synchrony of reproduction and the peak in food resources has been examined within populations, but not among populations. This thesis addressed these shortcomings. In order to examine the effect of foraging proficiency on fitness, nine American Dippers were observed foraging in the field when they were 39-42 days post-hatching. Individuals were observed for 8-18 bouts totaling 47-145 minutes of observation per bird. The rate of calorie intake was estimated by noting the length of the prey relative to bill length, multiplying the number of items by size-specific energy constants, and dividing total calories by foraging time. The rate of calorie intake varied (mean ± SD=44.6 ± 5.3, n=9) among individuals and showed a significantly positive correlation with hematocrit (r=0.79, P < 0.02, n=8). As hematocrit is a relative measure of condition and the condition of recently independent juvenile birds often indicates survivorship through the first year, these data are consistent with the assumption that greater foraging proficiency confers fitness benefits for free-living birds. This study also described the breeding biology of a population of American Dippers nesting in northern Utah and compared the measured parameters to published values for other Cinclid populations. Annual productivity appeared to be a function of the number of breeding attempts that could be completed within a breeding season. In turn, breeding season length may have been largely determined by latitude and stream pH. The observed geographic variation in the annual production of dippers may have reflected behavioral adjustments to local abiotic conditions determining food supply and breeding season length, suggesting that similar processes contribute to intrapopulation and interpopulation variation in reproductive behavior.

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