ABSTRACT
The osprey (Pandion haliaetus) has a nearly cosmopolitan distribution, but breeds primarily in the Northern Hemisphere. Northern populations migrate south to winter. The best time to census ospreys is during the incubation period which lasts about 38 days. It is relatively synchronized in temperate North America, but varies with latitude and altitude, generally beginning in late April to early June. In southern breeding areas, such as southern Florida and Baja California, the nesting season is less synchronized and immature birds are present, both of which complicate censusing. Aerial censuses, using a high-winged aircraft or helicopter are most practical for breeding ospreys. Osprey nests are large and are usually conspicuously placed at the top of a tree or artificial structure. During the census, it is important to record the nest structure, the habitat, and whether the nest is occupied by an incubating bird or by a nonbreeding pair.
