Stein, R.W.*; Williams, T.D.; Place, A.R.; del Rio, C.M.: Age-related differences in digestive function during migration in the Western Sandpiper (Calidris mauri)

It is common practice to use species’ mean values of standardized measures, such as BMR, to evaluate changes in energy demands. However, relying upon species’ mean values becomes problematic when age-related differences are large and are not accounted for. The problem becomes pronounced when conservation decisions are being made, i.e. preservation of particular migratory stop-over sites, on the basis of these measures. I use the digestive tract as a model system to evaluate individual performance in relation to meeting the energetic demands of migration. I evaluated functional aspects of the digestive tract at three levels: a) uptake rates across epithelium using the everted sleeve, b) morphology (histological analysis) and c) activities of two digestive enzymes (pancreatic lipase and aminopeptidase-N) in three age-classes of the Western Sandpiper (Calidris mauri) during migration. I present these data in the context of whole organism performance and differences in energy demands for the different age-classes. In particular I will show that there appear to be problems associated with the use of the everted sleeve method (extensive tissue damage during eversion) in free-living birds (cf. captive birds that have been used in many previous studies). This may relate to changes in gut structure associated with captivity per se.