STEIN, R.W.; WILLIAMS, T.D.*; Simon Fraser University, Burnaby, B.C.; Simon Fraser University, Burnaby, B.C.: Age-related variation in small intestine size in the Western Sandpiper (Calidris mauri): Early ontogeny, stage of migration, and cestode infection

The Western Sandpiper (Calidris mauri) exhibits age-related variation in small intestine size during fall migration; however, the causal factors and functional importance of this difference are unclear. This study was designed to examine the temporal onset, possible causes, and functional significance of this age-related difference in small intestine size. We collected premigrants and migrants (Alaska and British Columbia, respectively) to investigate age-related and migration-related changes in small intestine size. Prior to initiating fall migration juveniles had 10% longer small intestines than those of adults. This suggests that the observed age-related difference in small intestine size was primarily due to an ontogenetic effect. However, after a relatively long migratory flight the small intestines of both adults and juveniles increased in length (9% and 6%, respectively) and diameter (7% and 13%, respectively); this is evidence for a training effect associated with commencing migration. Among refueling birds, juvenile had a higher prevalence of cestode infection than did adults. Infected individuals had heavier small intestines (after controlling for length, body mass, and year effects) than uninfected individuals in both adults and juveniles (7% and 11%, respectively).