The influence of environmental conditions on aspects of the time budgests of breeding ospreys

Summary

Ospreys (Pandion haliaetus) were observed for 350 h in 1975 in southeastern Virginia. Other studies have demonstrated that weather can have an effect on aspects of osprey foraging behavior (e.g., frequency of diving), but for the environmental conditions observed in this study, weather and other variables did not appear to limit the ability of ospreys to feed their young.

Male ospreys, which procure essentially all of the food for the family unit before the chicks fledge, spend an average of 43% of the daylight hours perched near the nest when they have unfledged young. About 1/3 of the daylight hours are utilized for hunting. Weather conditions have no effect on the time the male his perched near the nest, or on the rate of fish delivery by the male. Wind speed variability regressed positively with the time it took males to return with a fish (mean time=0.64 h/fish), but accounted for only 16% of the variation in the length of hunting trips. Size of fish delivered and rate of fish delivery were unrelated to either brood size or age of young. As the chicks age, the male spends increasing amounts of time away from the nest; this is not related to changes in weather, and appears to be due to decreasing attentiveness at the nest site by the male. Females with unfledged young spent over 95% of the daylight hours at the nest.

Adults with fledged but dependent young spend an average of 1/3 of the day perched near the nest. Both adults deliver fish at this time, but together they bring no more than the male alone brought before fledging. For both adults neither the percentage of time perched near the nest nor the rate of fish delivery are related to weather conditions.