Me. Ciminari et al., Is diet-shifting facilitated by modulation of pancreatic enzymes? Test of an adaptational hypothesis in yellow-rumped warblers, AUK, 118(4), 2001, pp. 1101-1107
Many birds exhibit seasonal switches in diet and thus alter nutrients predo
minating their food intake. We tested for dietary modulation of pancreatic
enzymes in Yellow-rumped Warblers (Dendroica coronata), a species for which
such dietary changes are documented. Birds were fed three diets formulated
from either fruit, insect, or seed. We predicted that pancreatic carbohydr
ase amylase, and the proteases trypsin and chymotrypsin, would be modulated
in direct correlation with relative levels of dietary carbohydrate and pro
tein, respectively. In contrast to the prediction, there was no significant
dietary effect on activities of amylase and chymotrypsin, and a significan
t change in trypsin activity (highest on seed diet) occurred in the wrong d
irection with regard to the prediction. Considering the statistical power o
f our tests, we conclude that Yellow-rumped Warblers represent a case of on
ly modest ability, at best, to modulate pancreatic enzymes. For some diets,
especially high-starch diets that they digest relatively poorly and on whi
ch they tend to lose body mass, they may lack sufficient enzyme and hence a
re constrained in their dietary niche.