Environment

Osprey Facts: Animals of North America

These numerous birds of prey can build nests that are so large, they can even accommodate a human being.

Physical Description

Ospreys, or Pandion haliaetus, are fish-eating birds of prey with a large size and spectacular appearance. The size of this bird usually ranges between 21 and 23 inches (54 and 58 centimeters) with a weight of about 2.3 to 3 pounds (1.2-1.4 kilograms), with their wingspans extending out to about 5 or 6 feet (1.5 to 1.8 meters). The dorsal parts of this avian species, including the back and upper wing coverts, are of a deep, chocolate brown in color, while their ventral regions are primarily white. Their breasts are white with some brown speckling. The Ospreys' crowns and foreheads are mostly white, with a dark line running around the eyes and extending to the sides of the neck. The color of the birds' irises are yellow, with a pale blue, transparent, nictitating membrane . Even though the sexes in Ospreys are quite similar in appearance, a few visible differences can be used to distinguish them. Adult males usually have a slimmer body and narrower wings than do females, with females usually attaining body masses 15-20% higher than do their male counterparts upon reaching physical maturity. The brown streaks on the breasts are usually darker and denser in females than in males. Juveniles of this species are similar to adults, except for the orange-red color of their irises in their first years, and a scaly appearance of the back and wing coverts, an appearance that is due to the light buff-colored edges of their first feathers, which are lost by the time they see their first winter.

Diet

Either marine or freshwater fishes may comprise the lion's shares of the diets of Ospreys. Since these birds are unable to dive further than 0.5-1.0 meters deep into the water, their food sources are primarily restricted to those fishes that are to be found in shallow waters or surface schooling fish. The average size of their prey ranges between 8 and 14 inches (20 and 36 centimeters). The penetrating vision of the Ospreys can detect underwater movements from a height of 10 to 40 meters (33–131 feet) above the water's surface. After marking their targets, the birds hover over the water for a few moments before plunging into the water, feet first, to grab hold of their prey. This avian species is well designed by nature to meet its predatory foraging habits. With sharp spicules underneath its toes, talons with backwards-facing scales, and nostrils that can be closed when diving into water, the efficient predator is well equipped to succeed easily in its efforts to catch fish.

Habitat and Range

Ospreys usually frequent areas with shallow fishing grounds, or deeper waters where fish school near to the surface. Areas with expanses of shallow, fish-filled waters, such as lakes, marshes, lagoons, and rivers, serve as ideal habitats for these birds to thrive. After peregrine falcons, Ospreys are the second most common bird of prey, or raptor, in the world. Except for Antarctica, they are to be found in the tropical, sub-tropical regions, and temperate of all other continents. In summer, Ospreys are found found in North America from Alaska to Newfoundland and further south towards Florida and the Gulf Coast. During this season, they also breed in all parts of Europe. The Ospreys migrate along the coasts towards South America, South and South-East Asia, and Northern Africa during the winter season. In Australia, these birds primarily have a sedentary presence lacking major migrations. Golden eagles, bald eagles, great horned owls are the most common natural predators of these birds. During the period lasting from the 1950s until the 1970s, Osprey populations plummeted significantly, due to the rampant use of pesticides which poisoned these birds and thinned their egg shells. However, strict implementation of bans on harmful pesticides, such as the 1972 DDT ban, helped in bringing Osprey populations back up to safer levels. Conservation status results, provided by the American Breeding Bird Survey, exhibited an encouraging increase in Osprey populations, demonstrating a rate of 2.5% growth per year between 1966 and 2010.

Behavior

Ospreys are usually solitary in nature, and typically roost alone or in small groups of six to ten. They are known to defend their immediate nesting sites, usually from other Ospreys, though they are not strictly territorial, setting them apart from most other fish-eating birds. Aerial chases to defend nests are quite common among these birds, and can even become quite intense in certain cases. They prefer roosting in open areas, such as the bare branches of trees, and may also roost upon the ground for warmth on cold days. Hatchlings are known to aggressively compete over food sources, often resulting in the elimination of their weaker, later-hatched members.

Reproduction

Ospreys are found to mate for life, though rare cases of polyandry have been reported. During the breeding season, a pair of male and female mates will enter into a 5-month-long period of partnership in order to raise their offspring. Nests are cautiously built by the mating partners using sticks, with a compact lining of algae, sod, vines and other such materials inside them. The male is primarily involved in the gathering of all of these materials, while the female arranges them to build the nest. Nests built in the pair’s first season are usually small but, as consecutive years pass by, the nests can become large, some sizable enough to even accommodate a human. Within a month after mating, between 2 and 4 whitish eggs, with distinctive patches of reddish-brown colors, are laid by the female. The average time between the hatching of the eggs and their physical development into fledgelings usually lasts around 10 weeks.

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