Long-Term Monitoring of Osprey Populations in Western Montana

Abstract

Ospreys (Pandion ha/iaetus) are important apex predators and continue to be important indicators for environmental contaminants in aquatic ecosystems. Although osprey populations made rapid recoveries in Montana after the 1972 ban on the use of DDT, there have been surprisingly few studies monitoring osprey populations since then. During the last 20 yrs some osprey populations in western Montana have declined over 75 percent, and are now approaching the low numbers of the DDT era. The causes and geographical extent of these declines are not known. although companion studies have shown some very high levels of mercury in osprey chicks. For these reasons, we are establishing a long-term monitoring program for ospreys in western Montana. Here we report on our osprey studies on Flathead Lake and adjacent watersheds, which appear to be a major stronghold for ospreys. During the summer of 2008, we located and monitored 87 osprey nests on Flathead Lake. At least 69 (80%) of these nests were occupied; a sub-sample of 47 of these nests had 1.9 chicks produced per productive nest. This is above the productivity estimated to maintain stable osprey populations.