Bald eagle and osprey

Abstract

Bald eagles nested in all nine western states during recent years (about 19% of known U.S. population in 1982). The known numbers of nesting pairs in the west increased substantially in the last 10 years and totaled 584 in 1986. Much of the increase was due to more intensive survey efforts, but most biologists cite examples of new palrs establishing nesting territories. In contrast, productivity was relatively stable at 0.9 young produced per occupied territory with small annual fluctuations, a level slightly below the requirement for delisting (1.0 young per occupied territory) by the Pacific States Bald Eagle Recovery Plan. About 4,500 to 6,000 (minimum estimate) bald eagles winter throughout the western United States, which is about 50% of the surveyed population in the contiguous 48 states. Osprey range expansion and population increases have been documented in the West since 1981, when the population was estimated at 1,472 palrs (i.e., about 18% of the U.S. population). Monitoring efforts in the 1980s were not as intensive for ospreys as for bald eagles, but productivity was usually at the upper end of 0.95 to 13 young per occupied territory (a rate generally believed adequate for population stability). Although bald eagle and osprey nesting populations and productivity show cause for optimism, organochlorine contaminants remain a problem in a few individual birds and in some localized areas (e.g., lower Columbia River). DDE residues high enough to reduce productivity have been documented in eggs of both species during the 1980s. In addition, the bald eagle, which also forages on sick or dead prey, has been exposed to lead shot and the organophosphorus insecticide famphur. These contaminants have killed numbers of them in the West in recent years. Nesting ospreys appear more tolerant than nesting bald eagles of man and his disturbance; thus, more restrictions are required at bald eagle nest sites. Furthermore, bald eagles winter within the United States and their specific wintering requirements are generally known and considered in the species' management, whereas western ospreys winter in Mexico and Central America where knowledge of their requirements is nearly nonexistent. Reintroduction worked successfully for both species elsewhere but is not a high ,priority for western localities because few populations were extirpated and most populations have increased.