Age-related variation in the nutrient reserves of breeding American Coots (Fulica americana)

Abstract

We analyzed the relationship between age and nutrient reserves of 186 American Coots, Fulica americana, collected in southern Manitoba during the breeding season in 1981. The first principal component from the correlation matrix of 13 morphological variables was used as the measure of body size. Protein reserves, as indexed by lean dry weight, and fat reserves were related to body size, but the relationship for fat reserves was weak. The oldest coots of each sex were the largest, and this partly explained their larger protein reserves compared with the youngest coots. However, by scaling different sex–age groups to the same body size, we found that older coots had relatively larger protein reserves before breeding than did younger coots. Males and females did not differ in relative protein reserves, but females had relatively more fat reserves than did males. The results also indicated that body size is an important consideration in studies of nutrient reserve dynamics.