03. Chickadee Notes

Osprey in New Brunswick

Status

OspreyThe Osprey, or Fish Hawk, Pandion haliaetus, has a global range that is among the widest of any bird of prey. The species breeds throughout the northern hemisphere, as well as northern Asia and Australasia. It is estimated that there are 25,000 to 30,000 pairs worldwide. That the Osprey does not breed in Africa, South America, or Indomalaysia remains a puzzle. Although the Osprey is uncommon throughout New Brunswick, it is fairly common locally along the coast. The most dense breeding populations in New Brunswick occur mainly in coastal areas with extensive shallow waters, but Osprey also nest in numbers near lakes where fish are plentiful. Breeding Osprey are largely absent from the upper Bay of Fundy, where muddy water prevents visual detection of fish.

The use of the insecticide DDT led to increased reproductive failure in Osprey over the eastern United States during the 1960s. Osprey populations in New Brunswick may also have been reduced through the use of DDT, applied widely to provincial forests from 1952 to 1967 to control the spruce budworm. The species was first protected in New Brunswick under the Endangered Species Act in 1976. Although information on Osprey populations in New Brunswick was lacking at that time, extensive Osprey surveys were carried out in the province in 1974-75. Since these first surveys numbers of Ospreys nesting in New Brunswick have increased significantly, supporting suggestions that the population may now be recovering from a past decline. Today there are at least several hundred nesting pairs of Osprey in New Brunswick and the population may still be growing.

Natural History

In flight, the long, narrow wings of the Osprey, with their conspicuous crook and black wrist mark, confirm identification of adults and young at a great distance. Overall, the Osprey is dark brown above and white below. Female Osprey, with a wingspan of about 163 cm, are somewhat larger than males.

Osprey have a repertoire of vocalizations, ranging from a whistled "chewk, chewk, chewk" to a sociable "chirrup" exclaimed when greeting one another. However, it is the high-pitched whistle that these birds utter as they soar over water in search of fish that so often attracts the observer's attention.

Osprey have a preference for rivers, lakes and coastal bays...

With few exceptions, Osprey catch and feed on live fish only, and are well adapted to do so. These birds hunt mostly on the wing, soaring, hovering, and finally lifting the wings and plunging feet first into the water to grasp a fish. Short, sharp, horny spicules, unique among birds of prey, cover the base of the foot pad and ensure that slippery fish can be securely grasped. The talons, long and razor sharp, can snap shut in 2/100 of a second. Extra dexterity and stability for subduing fish is provided by the flexible outer toe, which reverses position and lets the bird grip with two toes forward and two toes back. The legs are long and unfeathered, allowing the bird to reach as much as a metre into the water at the end of a plunge. Fish can be spotted over water by the keen sighted Osprey from heights of up to 30 m.

Osprey have a preference for rivers, lakes and coastal bays, where they feed on a variety of fish, such as flounder, herring, menhaden, suckers, sunfish, and perch. They are not particularly choosy, taking those species which are most abundant, accessible, and the right size. On rare occasions Osprey have also been recorded preying on small mammals, birds, snakes, and molluscs.

In the spring, Osprey return to New Brunswick in mid-April...

North American Osprey are migratory. Most winter in Latin America and the Caribbean basin, with concentrations in northern South America. In the spring Osprey first return to New Brunswick in mid-April, appearing first in Charlotte County and along the lower St. John River. Gradually, birds move up the Saint John River valley and along the coast. Within about a week, Osprey start to appear in central New Brunswick and in about 10 days in the eastern counties. On the North Shore birds sometimes arrive in advance of those in the central and western parts of the province. This may be because they migrate on a broad front, entering New Brunswick in the north and inland as well as along the coast. Most Osprey have left New Brunswick by the end of September, but stragglers may remain into October or November, or even December.

...power blackouts in New Brunswick have been attributed to Osprey activity around hydro towers.

For about two weeks after birds arrive they are occupied repairing old nests or establishing new ones. Osprey are noted for their use of conspicuous and sometimes unusual nesting sites. In one case the bird, sitting on a nest placed on an unused windmill, was observed to go round and round with every breeze! The tops of isolated, flat-topped trees, live or dead, are most commonly chosen nest sites but birds frequently nest on other structures such as power poles or hydro towers. On several occasions, power blackouts in New Brunswick have been attributed to Osprey activity around hydro towers. Sites are invariably near water and exposed, giving the Osprey clear access when landing. One of the greatest nest densities in New Brunswick occurs at the Tabusintac Lagoon, where at least 20 nests have been observed.

The nest is a bulky structure of sticks, but unlikely items such as barrel staves, rubber boots, feather dusters, dolls, plastic hamburger cartons, and even animal carcasses are also sometimes incorporated. Both the male and female share nest construction duties. It is not unusual for a well-constructed nest to be used by several generations of birds, if the sheer weight of the nest does not cause the tree to collapse first.

By mid-May, New Brunswick Osprey have laid their two, or occasionally three, attractive buffy white and brown blotched eggs. Incubation lasts about 35 days, and by mid-August most young are on the wing. Although adult Ospreys have few enemies, their eggs or nestlings are preyed upon by gulls, herons, ravens and raccoons. Field studies in New Brunswick have shown that the yearly proportion of Osprey nests which are successful may vary from a low of 37% to a high of 76%. Successful New Brunswick nests produce from 1.7 to 2.0 young annually, comparing favourably with other parts of eastern North America.

Nearly all of the incubation is done by the female, with the young breaking out of the eggs at intervals. Their first down is short, thick, and buff-coloured and will be replaced 10 to 12 days later with a dense, woolly second down. By this time the young are active and moving about the nest. Growth is rapid, so that 70 to 80% of adult body weight is attained within a month of hatching, although fledging will not occur until the age of 40 to 55 days. Young Ospreys still depend on their parents for food for at least 10 to 20 days following first flight. Finally, at the age of about four months, the young will be skilled enough at catching fish to survive on their own and will join adults for the fall flight to the southern wintering grounds. Juvenile Osprey remain south for two or three years, after which they will have reached sexual maturity and will fly north to breeding areas such as New Brunswick.

Helping Out

Although the Osprey is a locally common bird in New Brunswick, the species has declined elsewhere, and populations are still recovering. Like all birds of prey in New Brunswick, the Osprey is protected. Nesting birds should not be disturbed, and because nests are used repeatedly trees with nests should not be cut at any time of the year. We can all help wildlife such as the Osprey by minimizing or eliminating our use of pesticides. When pesticides are used pesticide containers must be disposed of with great care.

Further Reading

Bent, A.C., 1936. Life Histories of North American birds of prey. United States National Museum Bulletin 167. 409 pp.

Poole, A.F., 1989. Ospreys: A natural and unnatural history. Cambridge University Press, Cambridge Massachusetts. 246 pp.

Stocek, R.F., 1972. The Occurrence of Osprey on electric power lines in New Brunswick. N.B. Naturalist 3: 19-27.

Stocek R.F. and Pearce, P.A., 1983. Distribution and reproductive success of Ospreys in New Brunswick 1974-1980. pp. 215-221. In Bird, D.M. (Ed), Biology and Management of Bald Eagles and Ospreys. Harpell Press. St.-Anne-de-Bellevue, Quebec. 325 pp.