Bird of the Month: Osprey
Written by Andy McCormick
Andy McCormick, Volunteer and Former Board President of Eastside Audubon
A powerful totem of conservation, the Osprey suffered dramatic losses in the mid-20th Century due to DDT pollution, but the species has now recovered to exceed its historical numbers and breed in a wide variety of habitats.
The Osprey is a fish hawk and has a special place in the world’s avifauna. It is the only raptor that plunges into water to catch live fish, and it is specially adapted to this lifestyle. Its wings are long and narrow, and large in relation to its body mass. This feature endows the Osprey with greater maneuverability than some larger raptors and the capability to rise out of the water with a fish in its talons and carry it a long distance to its nest. The diet of Ospreys is almost completely fish. However, the fish species will differ with location and may consist of mullet, smelt, flounder, bullhead, or other fish in the area. Photos, video, and vocalizations of Ospreys can be found at The Macaulay Library.
VERSATILE FLIGHT ABILITIES
The Osprey flight is described as languid and gull-like as it soars. While foraging, it flies slowly over water watching for fish. Once ready to strike, the Osprey hovers briefly then plunges at an angle into the water. In the last few seconds of flight, it will turn its body and dive feet first capturing the fish in its talons, often completely submerging in the process. The powerful wing strokes needed to take off from under water with the extra weight of prey are supported by increased muscle in the deltoid region of the wing (Bierregaard, et al). Spike-like pads on the feet of the Osprey cement its hold onto slippery fish. Once back in the air, the Osprey shakes off excess water and moves its outer toe to align the fish in a headfirst direction during flight (Alderfer).
A few years ago, I observed the flight agility of an Osprey over Rattlesnake Lake as it was being chased by a Bald Eagle. The Osprey was carrying a fish and the eagle was trying to get it to drop its prey. By accelerating and increasing its altitude in a spiraling flight, the Osprey out maneuvered the eagle, which could not maintain the rate of the climb or the speed of the Osprey. The eagle soon gave up the chase and the Osprey flew off with its fish.
Osprey
Scientific Name: Pandion haliaetus
Length: 23”
Wingspan: 63”
Weight: 3.5 lb (1,600 g)
AOU Alpha Code: OSPR
STRONG MATE AND SITE FIDELITY
An Osprey pair may stay together and will return to the same nest for many years. The nest, built by both sexes, is a bulky mass of sticks constructed at the top of a tree within a short flight to water. The Osprey’s nesting behavior includes adding sticks each year resulting in an expanded nest over time. Some Osprey nests have been known to weigh 300 lbs. or more. Ospreys tolerate the presence of humans near their nests and are comfortable using structures such as utility poles and roofs of buildings. They have also taken advantage of nest platforms constructed specifically for them and in some locations prefer them to more natural locations. Once the pair is settled, three eggs are deposited in the nest. For about 40 days, the female does most of the incubation. First flight occurs at about eight weeks of age (Kaufman).
The sole member of the genus Pandion, named for a mythological king of Athens, the Osprey is also the only member of the family Pandionidae. Presumably, it has been afforded this status because of its fish catching specialization. Its species name haliaetus is from the Latin haliaetos, a sea eagle. The English name Osprey is from the Latin ossifragus, from os, bone, and frangere, to break. This name was originally given to the Eurasian Bearded Vulture (Gypaetus barbatus) also known as the Lammergeier, a large vulture that drops bones and turtles from the air to break them. It is not known why the name was transferred to the Osprey sometime in the 16th Century (Holloway).
STATUS AND DISTRIBUTION
The Osprey is considered a species of Least Concern (BirdLife International) with a world population of 100,000 to 120,000 individuals. Information available in 1985 put the world population of Ospreys between 24,000 and 31,000 pairs with 7,000 to 8,000 in the contiguous United States, and another 10,000 to 12,000 in Alaska and Canada. However, the Osprey population is expanding and by the mid-1990s there were estimates of increases of 50 -100% in some areas. By 2001 the continental U.S. population had increased to between 16,000 to 19,000 pairs (Bierregaard, et al).
Ospreys nest in the subarctic across North America, Europe, and Asia and most migrate completely out of the breeding zone and winter in a zone across Central and northern South America, Africa, Southeast Asia, Indonesia, and the coast of Australia. Some non-migratory populations remain in the Mediterranean region. Most Ospreys have migrated out of Washington by the end of September and return to the breeding range in late March to April (Aversa, et al).
Photo credit Mick Thompson. References available upon request from amccormick@eastsideaudubon.org.