Montana Field Guide

Osprey - Pandion haliaetus

Ospreys are dark brown above and white below, with a barred tail. The head is white with a prominent brown eye stripe extending from the eye to the shoulders. Females and immature birds have brown streaking on the breast. Immature ospreys have light feather edges on the tops of their wings, giving them a speckled look. Ospreys have long, narrow wings, which are bent at the wrist when soaring. The underside of the wing often appears two-toned, with white along the leading edge of it (except for dark wrist patches), and brown-barred flight feathers. They have a loud whistled call. Ospreys range in length from 21-24 inches, and have a wingspan of 54-72 inches (FWP). A large diurnal raptor with long narrow wings, dark brown upperparts, white underparts, a white head with a prominent dark eye streak, and dark wrist patches (visible in flight) on the underside of the wings; immatures have pale buff edging on the dark feathers of the upper surface; females are more likely than males to have a necklace of dark streaking; average length 56-64 cm, wingspan 147-183 cm (NGS 1983).

Bald eagles are much larger and hold their wings straight out when soaring. eagles have dark brown bellies and wings, in contrast to the white belly and barred wings of the osprey (fwp). differs from other hawks in having all of the following characteristics: white belly, dark wrist patches, and a white head with a prominent dark eye streak. other hawks do not habitually plunge feet-first into water to obtain prey.

Montana Range

Ospreys depart by October for wintering areas in Central and South America (FWP). Bozeman area migr.: Apr 20-May 1 & Sep 15-30 (Skaar 1969). Migrates to CA, TX, FL or farther south.

Ospreys nest mainly near large lakes, reservoirs, and rivers in Montana (FWP). On upper Missouri, nest tree height variable but always as tall or taller than other trees. Presence of a flat, stable surface for nesting more important than tree species (Grover 1983).

Nearly all of their diet consists of fish, primarily rough fish such as suckers (FWP). On upper Missouri, catastomids most common prey, with salmonids & cyprinids eaten in similar quantities. Perch also eaten, but relative frequency not calculated (Grover 1983).

Upper Missouri nesting density = 0.03 occupied/km free flow- ing river, 0.54 occupied/km impounded river (Grover 1983). Becoming rare in Fortine area. Considered common 100 yrs ago in Gallatin valley; uncommon today (Skaar 1969).

Ospreys build their large nests on trees, power poles, docks, and other man-made structures. Ospreys prefer to build their nest at the top of dead, broken-topped trees, unlike eagles, which usually build nests in live trees below the tree canopy. Ospreys often build "frustration" nests if their first nest fails, although they rarely lay eggs a second time. Ospreys arrive in Montana in March and April, and lay one to four eggs in April or May. The young leave the nest in July and August, when about two months old (FWP). Upper Missouri ave. clutch = 2.71; 2/3rds of pre-fledglings killed were blown out. Successful nests = 52% of total occu- pied. Brood size of successful nests = 2.16. No eggs layed in 21.7% of occupied nests (Grover 1983). Nest dates Apr-Jul.