Date of Award
Doctor of Philosophy
For many species of birds, egg formation costs are considered important constraints on timing of breeding, clutch size, and egg size. For American Coots (Fulica americana), body reserves and current food availability are both thought to affect these aspects of reproduction. In order to test the egg formation hypothesis, I conducted numerous observational and manipulative experiments on wild, free-ranging American Coots. Clutch size declined with laying date in five out of six years, contrary to seasonal patterns of food availability in prairie wetlands. Clutch size increased during two of three years in response to supplemental feeding. Laying date was only slightly affected by food supplements. Coots renested rapidly following clutch destruction, and some females produced phenomenal numbers of consecutive or near-consecutive eggs (to a maximum of 35 in 37 d). Because the average clutch was usually 8-11 eggs, these data provided a strong refutation of the egg formation hypothesis.;Egg size exhibited little change in response to most factors, and egg composition was only slightly more sensitive to such factors as annual variation and supplemental feeding. Egg size and quality (relative protein, lipid, and energy content) were positively correlated with clutch size, contrary to predictions based on life-history trade-offs. I suggest that among-individual variation in "inherent quality" overshadows these expected trade-offs.;Analysis of nutrient reserve dynamics of adult coots did not support earlier claims that coots rely on stored fat and protein for egg production. In general, coots exhibited little sign of nutritional stress during breeding, although supplemental feeding did result in increased fat and protein reserves. Among postlaying female coots, there were significant positive correlations between size of reserves and measures of previous reproductive performance. These observations lend further support to the idea that individual females are inherently "superior" or "inferior" breeders, but they do not give any indication why this might be so.;I conclude that coots are not food limited during egg laying or incubation. Further work is needed on the potential role of food limitation during brood-rearing, particularly with regards to variation in brood size and hatching asynchrony.
Arnold, Todd William, "Food Limitation And The Adaptive Significance Of Clutch Size In American Coots (fulica Americana)" (1991). Digitized Theses. 1954.