Factors affecting plasma biochemistry parameters and physical condition of Osprey (Pandion haliaetus) nestlings

Abstract

We assessed the normal values for 15 blood plasma biochemistry parameters and three indices of body condition (IBCs) in free-living Osprey (Pandion haliaetus) nestlings in Brandenburg (Germany). Values were compared with those of other raptors, and possible sexual and age-related differences were examined. In addition, we looked for possible relationships of habitat quality (measured in terms of foraging conditions and human disturbances) to nestling nutritional condition and productivity. Female nestlings showed higher mean urea levels and lower glucose values than males, which could be related to higher growth rates and nutrient demand of females at the end of the nestling period. Seven parameters also showed variation with age, probably relating to increasing body mass, metabolic rates, and physical activity during the pre-fledging stage. Conversely, the IBCs showed poor correlations with selected nutritional parameters, probably due to the homogeneously acceptable nutritional conditions of the nestlings. Finally, we found that Ospreys did not seem to adjust initial parental investment in relation to habitat quality, since productivity was not affected by habitat indicators. However, in large broods, but not in small ones, nestling nutritional condition improved as foraging conditions improved. These results suggest that females that are in better physical condition seem to produce more and better nourished nestlings in better foraging conditions.