Blood glucose concentrations during breeding in Short-tailed Shearwaters

Abstract

Blood glucose concentration was measured in breeding adult and non-breeding immature short-tailed shearwaters (Puffinus tenuirostris) at key stages during the breeding cycle on Phillip Island, Victoria. The species' diet has a low carbohydrate content, but its mean whole blood glucose level of ~14 mm L^-1 was comparatively high; however, this may partly have resulted from the procedure of sampling birds relatively soon after they returned to the colony at night after daytime feeding. Mean whole blood glucose level was significantly, but not dramatically, higher (by about 3 mm) during the incubation stage than at other times during breeding. This pattern was not related to breeding energetics, because it was exhibited by both age-classes. It may have reflected systematic variation in the recent feeding history of the sampled birds over the breeding season. Coefficients of variation in whole blood glucose concentration within samples obtained across the breeding cycle ranged from 13.7 to 20.8%. This level of variation is a little higher than that observed during the fasting-feeding cycle of other bird species, but might be expected in a species that exploits patchily dispersed food resources.