Osprey Pandion haliaetus

  • Order: Accipitriformes
  • Family: Pandionidae
  • Polytypic: 4 subspecies
  • Authors: Alan F. Poole
Sections

Appearance

Distinguishing Characteristics

northern migrant (carolinensis) Osprey perched, with caught fish. Pantanal, Mato Grosso, Brazil. 11 December 2006 © Arthur Grosset Large (approximately 1,400 to 2,000 g body mass), long-winged (150 to 180 cm wingspan) raptor with dark chocolate-brown back and upper wing coverts, mostly white breast (some speckling) and belly, white crown and forehead, and dark line through eye. Caribbean subspecies (P. h. ridgwayi) appears mostly white-headed and white-breasted (and often paler brown on back); North American individuals less so. Ospreys breeding in Mexico much like Caribbean birds, with breasts and crowns almost entirely white, also with white underwing coverts; females slightly but not significantly darker than males in both these populations, so sexes not reliably distinguished.  In all populations, iris of adult yellow; cere and legs pale blue-gray. Speckled brown necklace on breast of female (and some males).

Among Ospreys, sexual differences in plumage and size confuse the issue of geographic variation. Within populations, females average about 15–20% larger in body mass than males, and 5–10% longer in wing, tail, claw, and bill length. In addition, females tend to have fuller, darker breast-bands and darker heads than males, although this varies among populations (see above).

Juvenile similar to adult, but upperparts appear scaly because of light-buff feather edges on back and upper wing-coverts; these generally wear off by first winter; iris orange-red through first year.

Similar Species

Not easily confused with other birds of prey, except maybe adult Bald Eagle (Haliaeetus leucocephalus), which is larger, with all white head and tail. In flight, possibly confused at a distance with large gulls, especially adult Great Black-backed Gull (Larus marinus), but latter has all white head and tail, longer bill, white trailing edge to wing, and no crook to wings.

Detailed Description

Note that there are two subspecies of Ospreys found in the Neotropics: migratory carolinensis from breeding grounds in North America and (mostly?) resident ridgwayii that breed on Caribbean islands and shores, with a somewhat similar form nesting in northwestern Mexico. See Geographic Variation. Overall, Ospreys from tropical and subtropical climates tend to be paler than their conspecifics breeding in higher latitudes, in accordance with Gloger’s rule (Prevost 1983) and this pattern fits for Ospreys in the Americas: southern resident breeders are paler in plumage than their northern migratory counterparts. The following description is based on northern carolinensis, which occurs throughout the Neotropics as a migrant south to Chile and Argentina; see Summary and Geographic Variation for characters of resident Ospreys in the Caribbean and in northwestern Mexico.


Adult (Definitive Basic plumage): Forehead, crown and nape white, spotted with blackish brown (markings heavier on center of crown and nape). The eye is surrounded by a blackish brown ring, which then expands behind the eye in a wide blackish brown band that extends along the side of the neck to the back. Underparts mostly white, other than for a variable amount of dusky streaking on the sides of the throat and across the breast. The back, scapulars, rump, and upper surface of wing are dark brown; the primary coverts are almost as dark as the primaries. Upper surface of rectrices medium brown on outer webs; inner webs of all but the central pair are duller whitish. Rectrices crossed by about 5 (central rectrices) to 8 (outermost rectrices) dark brown bands, the most distal of which is the widest. The rectrices are tipped dull white.

Underwing coverts white, heavily barred or marked dark brown on greater secondary-coverts and the distal portion of the median secondary-coverts; the dark coverts on outer half of under wing surface form a conspicuous dark carpal-patch. Remiges dull whitish, barred with medium brown, and becoming darker on distal, narrowed portion of outermost 5 primaries. Axillaries brownish white and often with darker terminal marks.


The dark feathers of the nape, sides of neck, and anterior crown are elongated, forming short frontal and nuchal crests when erected.

Sexes are similar, except that the dark markings on chin, breast, and sides of neck average greater in females than in males; some males may appear all white in these areas or have minimal dark markings.

Juvenile similar to adult, but upperparts appear scaly because of light-buff feather edges on back and upper wing-coverts; these generally wear off by first winter; iris orange-red through first year.Osprey in flight. Pantanal, mato Grosso, Brazil, 02 December 2006, © Aruthur Grosset

Molts

Despite well-studied molts of Ospreys breeding at northern latitudes, molts of Ospreys breeding in the Neotropics largely have been ignored; the molts of southern and/or nonmigratory populations may differ (Henny 1988) and require further study. In older (adult) birds of both European (nominate haliaetus) and American (carolinensis) populations, Definitive Prebasic molt occurs mainly in 2 discrete periods, with main period on winter range (before migration to breeding range) and the other on breeding range (before migration to winter range) with most or all feathers renewed over a 12 month period. If the Neotropical breeders follow molt patterns roughly similar to Northern ospreys (perhaps not likely given that most resident breeders do not face the migration pressures of northern Ospreys), a quick summary suggests the following:


A) Primaries replaced in successive overlapping waves, each beginning with P1 and progressing out to P10, with number of feathers separating successive waves fewer in adults than in immature. Without this pattern of molt (often called Staffelmauser), Ospreys would require >1 yr of interrupted molt to renew all primaries given the same growth rates. Staffelmauser allows all primaries to be renewed annually (maintaining optimal aerodynamic capabilities of wing) in this and many other large bird species that are heavily dependent on soaring flight for survival.


B) Definitive Prebasic molt occurs mainly in 2 discrete periods: non-breeding period, especially 1-2 months leading up to breeding; and post-breeding, especially once female is released from the nest. Most or all feathers are renewed over a 12 month period.

Bare Parts

Bill dull blackish in adults, with cere, base of lower mandible, and commisure (extending from gape distally to nostril area) bluish gray.
Feet and unfeathered portion of tarsi covered with small, rough, scales that become large and flat on distal portion of upper toes, and smaller with sharp points on soles of feet. Feet large; outer toe reversible; talons long, robust, and strongly curved. Tarsi and feet pale bluish gray or sometimes tinged greenish; talons black. In most photographs, tarsi and feet appear very pale and dull whitish, with bluish color difficult to discern. Unique foot structure facilitates retaining grasp of slippery prey.

Measurements

Bahamas: MALE winglength -- 461 mm ± 7 SE; bill length -- 33.5 mm ± 3 (SE) (n = 4); FEMALE wing -- 492 ± 26; bill -- 36.1 ± 17 (Prevost 1983, museum specimens, n = 3).

Body mass: no published data for Caribbean, Mexico (Baja); for USA, see Poole et al. 2002, and above.  Males ca. 1200-1500 g; females ca. 1600-2000 g.

Recommended Citation

Poole, A. F. (2009). Osprey (Pandion haliaetus), version 1.0. In Neotropical Birds Online (T. S. Schulenberg, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/nb.osprey.01