osprey

English

Osprey
Pandior haliaetus
This information was scanned from The Birds of British Columbia (Campbell et al.), Volume II, pages 10-13. Volumes I, II and III of The Birds of British Columbia, can be ordered electronically at: orders@ubcpress.ubc.ca from UBC Press in Vancouver, British Columbia.

Range
Cosmopolitan Occurs in tropical and temperate parts of all continents. In the Western Hemisphere, breeds from northwestern Alaska and central Canada south to the Bahamas and from the southern United States south to Chile and Argentina.

Status
Uncommon to fairly common migrant and summer visitant across the southern third of the province, rare north of latitude 56°N very rare on the Queen Charlotte islands. In winter, very rare on the south coast, casual in the interior. Widespread breeder south of latitude 56°N, except the Queen Charlotte Islands.

Status Change
No change.

Nonbreeding
The Osprey is widely distributed throughout the province, occuring chiefly near lakes, rivers, sloughs, and protected coastal waters including lagoons, bays, and inlets it is reported infrequently on the Queen Charlotte islands and in far northern mainland areas

On the coast, the first spring migrants may be seen in late February, but most arrive during the first 2 weeks of April in autumn, the southward movement begins in September, and by mid-October most have departed. In the southern interior, early spring migrants appear during the second and third weeks of February, but the main influx occurs during the second and third week of April. Migrants arrive in the Chilcotin-Cariboo region during the first week of April. Autumn departure occurs during late August and through September. The main exodus in southern areas occurs during the last 2 weeks of September; most birds have departed by early October Migrating Ospreys do not regularly aggregate in large flocks in British Columbia as they do in some other areas in North America (see Bull 1974); the largest group reported in the province is 16 birds.

Breeding

Nests

Eggs

Young

The Osprey breeds throughout the province, except on the Queen Charlotte islands, generally south of latitude 56°N. Although Cumming (1931) indicates that it "... formerly nested at Tow Hill .. and is now absent from the north end of Graham Island [Queen Charlotte Islands]..." there is no conclusive evidence that it ever bred there. The centre of abundance appears to be in the vicinity of Creston and Nelson where approximately 140 pairs nest, making this area one of the most concentrated in the world (Anonymous 1988) The most northern record is from Atlin Lake (3 young in tree nest, 16 July 1980).

The Osprey breeds from near sea level to at least 1,070 m elevation in close proximity to permanent water. Occasionally, nests may be located up to 4 km from a source of water. Most nests (87%; n=361) were closely associated with permanent water. Nests close to water were found in the vicinity of lakes (65%), rivers (25%), or marine shores (9%). Three nests were located near drying sloughs. Lake nests were either situated on a man-made structure in the lake (52%), in trees along the shore (39%), or on wooded islands (9%). River nests were situated either along shores (67%) or me man-made structures in the river (23%). Nests on dry land (13%) were located on forested sides of mountains, lightly forested range land, along highways, roads and railway tracks, or on prominent, wooded hills. L S. Forbes (pers comm ) found that Ospreys at Creston sometimes nested be Great Blue Heron colonies. He also notes that Ospreys there give nesting Bald Eagles a wide berth and that a relocation of eagle nests caused a redistribution of nesting Ospreys

Nests:

Nests were situated in trees (56%; n = 395) and on manmade structures (44%). Most tree nests (64%) were in dead trees, including black cottonwood and 5 species of conifers. Living trees (36%) included 2 deciduous and 7 conifers us species Most nests were located at or near the top of the tree. Man-made structures supporting nests included wooden pilings (53%), cross members of wooden power poles (32%), navigation lights in lakes (8%), as well as cranes, artificial nest platforms, gas pylons, microwave dishes, a cable across a river, a wharf, and a chimney. Heights of 381 nests above ground or water ranged from 1 to 61 m, with 59% recorded between 9 and 18 m.

Nests ranged from compact to large, bulky structures of sticks, branches, and twigs. They were usually lined with a variety of material, including twigs, grasses, bark (black cottonwood and ponderosa pine), mosses, weeds, fish bones, twine, and down. Measurements for 8 nests ranged from 0.6 to 2.3 m for outside diameter, and 0.3 to 1.7 m in height.

One nest in the east Kootenay was used for 11 consecutive years. Two active Osprey nests built on a wharf were only 6 m from each other. Ospreys have been recorded displacing Canada Geese and Great Horned Owls from their nests, although at Creston, geese often prevent Ospreys from using a nest (L. S. Forbes pers. comm.). Forbes also notes that Ospreys occupying nests from which geese had fledged young rarely reared young successfully.

Eggs:

Dates for 46 clutches ranged from 30 April to 23 June, with 51% recorded between 15 and 22 May. Calculated dates indicate that eggs could be found as early as 17 April and as late as the end of June. Sizes for 39 clutches ranged from 2 to 4 eggs (2E-16,3E-21,4E-2), with 54% having 3 eggs. Incubation period is about 38 days but may extend to 43 days (Barber and Koplin 1972).

Young:

Dates for 419 broods ranged from 21 May to 4 September (2 young fledged), with 52% recorded between 27 June and 20 July. Sizes for 412 broods ranged from 1 to 4 young (1Y-117, 2Y-221,3Y-67,4Y-7), with 54% having 2 young. Fledging period is 44 to 59 days (Stotts and Henny 1975).

Remarks
In the Creston area, numbers of breeding Ospreys increased between 1968 and 1981. This increase was attributed, in part, to the installation of a water management system which increased the abundance of prey fish available to the birds (Flook and Forbes 1983). In 1981, a mean of 1.5 young was fledged from 27 occupied nests in the Creston area. This mean is above the rate necessary to maintain a stable Osprey population (Henny 1983,1986; Henny and Wight 1969; Spitzer et al. 1983).