The Osprey is most frequently observed near permanent water bodies which contain significant fish populations. It is a dramatic bird to watch as it flies over water scanning the surface for rising or basking fish. When a potential kill is detected it usually begins to hover. As it hovers it will periodically adjust its height and then plunge down hitting the water surface at its up to 45 miles per hour (70 kilometres per hour). As it enters the water, the wings are folded and swept back behind the tail. The feet are extended out in front of the body. When the fish is caught, the Osprey will unfold its wings, and make a powerful downthrust freeing it from the water. The fish will be adjusted so that the head points in the direction of flight. At times it will skim above the water, similar in method to a Bald Eagle, dragging its legs intermittently in an attempt to startle fish to allow easy capture. The frequency of foraging success appears to be quite high with average adult success from one study at 62% while another study reported 57.5%. The Osprey hunts most often in mid-morning and late afternoon, apparently independent of cloud conditions or wind speed. Yet these factors do impede success, probably because of limited visibility.
The adult Osprey, in autumn, migrates on average about two weeks earlier than do juveniles. The bulk of migration occurs in the middle of September. In eastern North America migration occurs on a broad front from the Appalachian Mountains east to the coastline. In the interior, and the west coast, the timing is similar but pathways are less understood. The Osprey returns to its breeding grounds in North America between early March and mid-May.
The Osprey generally begins mating at three years of age. Typically, a male returns first to an old nest site. He may perform elaborate flight displays such as flying backwards at near stalling speeds, or carrying a stick (or fish) and dangling it in what is thought to signify nest ownership. Nest building or refurbishing commences once the female has returned and she stands in the nest organizing sticks and twigs which are brought by the male. Polygamy has been observed at one study site in Massachusetts in the early 1970s. This is believed to have been the result of too few males or too many females. The unequal sex ratio seems to have been the effect of low productivity because of pesticide poisoning and long distance immigration by females from source populations.
The Osprey defends only the immediate nest site so that in areas with abundant food, local colonies can develop. In these areas nest sites can be as close as 67 feet (20 meters). In areas relatively poor in food supply, such as at the northern limit of the range in Quebec, nests occur one every 75 square miles (200 square kilometers).
ADAPTATIONS
The Osprey has evolved several novel adaptations which are unique among birds. The foot is remarkable in that it can turn backwards and has accompanying spines on the soles of its toes; both of which contribute to the ability for catching fish. Osprey feathers tightly overlapping in a regular pattern, are compacted, and oily; all three factors contribute to water resistance. The tarsi are short and relatively thick, possibly for resisting impact at high speeds on the water surface and the fish itself. The bill is strong and hooked and the small intestine is relatively long and narrow; thought to be a benefit for digesting scales and bones.
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Always carries fish head first
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Fish make up 98 percent of the diet
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Pair copulating; male on top
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