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The osprey is one of the most widely distributed birds in the world. They can be found wintering or breeding on every continent except Antarctica. Those who spend time on the water have likely seen these spectacular birds of prey, which resemble an eagle but with narrower wings. Ospreys are frequently seen in The Bahamas and their large bulky nests can be found on the cliffs and shorelines of many of our islands.
There are four subspecies of ospreys, which are separated by geographic region: (1) Pandion haliaetus carolinensis breeds in North America and the Caribbean, and winters in South America; (2) Pandion haliaetus haliaetus breeds in the Palearctic region ( Europe, North Africa and in Asia north of the Himalayas) and winters in the south Africa, India and the East Indies; (3)Pandion haliaetus ridgwayi is a non-migratory subspecies and it resides in the Caribbean with a range that extends from The Bahamas and Cuba to southeast Mexico and Belize; and (4) the final subspecies, Pandion, haliaetus leucocephalus is also a non-migratory subspecies. Its range includes Australia and the southwest Pacific.
Osprey can live almost anywhere where there are safe nest sites and shallow water with abundant fish. Nests are usually found close to water: rivers, salt marshes, mangrove swamps and along the shore of islands usually on high cliffs or rocky ledges.
Ospreys are large (55 -58 cm long) with a wingspan ranging from 145 to 170 cm. Their wings have a characteristic bend at the carpal (“wrist”) joints. They are bright white underneath with a mottled dark brown necklace. The North American race P. h. carolinensis has a dark eye stripe through each eye and a dark brown back. The beak is black and the feet are a pale blue–gray. Adults have a bright yellow iris but juveniles have an orange –red iris. The Caribbean subspecies P.h. ridgwayi is paler on the head and breast, but lacking the dark eye stripe.
Ospreys are unusual among raptors for their fish eating diet. They are generally opportunistic and will eat whatever fish species are available. They hunt for fish on the wing flying 10 to 40 meters above the water. When they spot a fish, they hover briefly and then dive toward the surface of the water. Just before hitting the water, the osprey swings its legs forward and bends its wings back, plunging feet first into the water, using strong wing beats to lift itself and its prey from the water. Once airborne the osprey rearranges the fish in its feet carrying it with one foot in front of the other so that the fish is facing forward. This supposedly makes the fish more aerodynamic and easier to carry.
Ospreys display several adaptations to their unique fish eating lifestyle. They have relatively long legs for a raptor, spiny footpads called spicules, long sharp curved claws and a reversible outer toe to aid in gripping slippery fish. Additionally, ospreys have dense oily plumage and efficient nasal valves that prevent water from entering the nostrils when the bird dives to catch a fish.
Ospreys build their nests high off the ground to protect the young from ground dwelling predators such as raccoons or snakes. They are adaptable, building their nests on channel markers, dead trees, artificial nest platforms, communication towers, buildings and other manmade structures. They are pack rats and will jam the nest walls with anything from boat line to Easter tinsel to plastic bags and even stuffed animals.
Courtship in ospreys centers around food and nest sites. Ospreys are generally monogamous although divorces do occur, usually because of infertility or a male being a poor hunter. Osprey pairs use the same nest year after year but they need to spend some time each year repairing it. Once the nest has been established the male begins to deliver food to the female. If the female is well fed, she will spurn the advances of other males. The feeding continues until the young fledge.
Ospreys usually lay from two-to-four eggs over a period of several days. Both the male and female incubate the eggs which hatch in about 40 days. Eggs hatch in the order they were laid. Chicks that hatch first are larger and have a competitive advantage over those that hatch later. If food becomes scarce, the smaller chicks often die. The breeding season differs between populations. Migratory populations usually nest in the spring and summer (April – May), while non-migratory populations breed in the winter and spring (December – March). Osprey chicks usually fledge between 48 and 76 days old. After fledging they begin to hunt on their own. However, they often return to the nest to receive food from their parents for two to eight weeks after fledging.
In the late 19th and 20th centuries, the main threats to osprey populations were egg collectors and shootings. These declined by the late 20th century, though some shootings still occur. The introduction of the pesticide DDT (dichloro-diphenyl-trichloroethane) caused osprey populations to decline from the 1950’s through the 1970’s. The banning of DDT in the U.S. contributed to the rebounding of the North American population but DDT continues to be used in some countries that serve as wintering grounds for ospreys. Ospreys are protected under the US Migratory Bird Act, CITES appendix II and the Bahamas Wild Birds Protection Act.
Ospreys are a valuable indicator species for monitoring the long term health of rivers, bays, and wetlands. They are well suited for this role due to their fish eating lifestyle and known sensitivity to contaminants. They are also relatively easy to study because of their highly visible nests and are tolerant of short term disturbance such as nest observation by researchers.
The resident Caribbean subspecies has not been widely studied and actual population numbers are not accurately known. The Bahamas National Trust would appreciate yachtsmen and residents who observe osprey nests and ospreys in The Bahamas reporting their location to the BNT at bnt@bnt.bs. GPS points for the nests would be most helpful.
Provided by the Bahamas National Trust.
The Bahamas National Trust would appreciate yachtsmen and residents who observe osprey nests and ospreys in The Bahamas reporting their location to the BNT at bnt@bnt.bs. GPS points for the nests would be most helpful.