Wiersma P., Piersma T. & Van Eerden M.R. (1995) Food intake of Great Crested Grebes Podiceps cristatus wintering on cold water as a function of various cost factors. ARDEA 83 (2): 339-350

Food intake rate during the nonbreeding season of Great Crested Grebes Podiceps cristatus was estimated by reconstructing the stomach content of drowned birds from recognizable remains of the fish prey. Food intake by individual birds since the ejection of the last pellet (the accumulated prey mass) was assessed by estimating fresh mass of ingested fish on the basis of otoliths and pharyngeal bones. We present arguments for a constant pellet ejection rate during the winter season, which is essential for interpreting the data. The large sample sizes enabled us to analyze accumulated prey mass for monthly intervals. We show that food intake varied considerably during the season, increasing 1.8 fold from October to January. Intake rate was even lower in September than in October, but during this time most adults are undergoing wing moult which involves a strong reduction in diving activity. We explore the extent to which several variables explain the 1.8 fold increase in food intake from autumn to mid-winter. Changes in the air and water temperature, time spent submerged, heating up food, diving depth, fattening and buoyancy can explain a total of 55% of the observed increase in food intake. The remaining 45% must be due to higher activity costs during winter, resulting from an increased food requirement.