The Annual Molt Cycle of Branta canadensis interior in Relation to Nutrient Reserve Dynamics

Abstract

During July 1984-February 1987, we measured the duration and seasonal changes in intensity of prebasic molt in Canada Geese (Branta canadensis interior) of the Mississippi Valley Population (MVP). Temporal and geographic variations in molt intensity were examined in relation to lipid and protein reserve dynamics and the chronology of annual events. Wing- and body-molt intensities were greatest before fall migration, but limited body molt overlapped migration and continued into fall. Final stages of molt progressed with declining intensity through winter. Only the nesting season (May-June) was entirely free of molt. Molt in individual geese may have required ≥8 months (July-March) in at least 60% of the population. Temporal and geographic variation in molt intensity were associated with differences in lipid mass, but carcass protein had little apparent relationship with molt intensity. There was no evidence of net catabolism of nutrient reserves between hatching, wing molt, and post-molting periods. Lipid masses of breeding females and non-breeding geese declined during wing molt. Protein masses declined during wing molt only in breeding and non-breeding males, due to atrophy of breast muscles associated with flightlessness. Seasonal changes in molt intensity and lipid reserves indicated that geese allocated energy to emphasize molting before fall migration, and nutrient reserve deposition thereafter. The largest nutritional costs of molting probably were incurred during July-November. We propose that rate, intensity, and duration of body molt were influenced by the amount of productive energy geese were able to allocate to feather growth, without compromising replenishment of nutrient reserves after breeding or the deposition of reserves before winter. The simple, single molt of Canada Geese provides greater latitude in adjusting nutritional demands to environmental conditions than is possible for ducks that molt twice annually.