Modulation of gut function is important in an ecological and evolutionary c
ontext because it likely determines what food items an animal can and canno
t eat. We examined how diet affects activity of digestive enzymes in an omn
ivorous bird, the pine warbler (Dendroica pinus). Pine warblers were fed in
sect-based, fruit-based, and seed-based diets for similar to 54 d. We then
measured activity of amylase, maltase, sucrase, aminopeptidase-N, trypsin,
chymotrypsin, carboxypeptidase A, carboxypeptidase B, pancreatic lipase, an
d carboxyl ester lipase. We predicted that carbohydrase activities would be
highest in birds fed the diet highest in carbohydrates (fruit based), prot
ease activities would be highest in those fed the diet highest in protein (
insect based), and lipase activities would be highest in those fed the diet
s highest in lipid (insect based and seed based). Also, we predicted that p
ine warblers would exhibit greater dietary modulation of enzyme activity th
an reported for a less omnivorous congener, the yellow-rumped warbler (Dend
roica coronata). All predictions were upheld, supporting the hypothesis tha
t pine warblers modulate the activity of digestive enzymes in proportion to
demand from substrates in the diet.