. The Canadian field-naturalist. 430 The Canadian Field-Naturalist Vol. 87 as a consequence are easier to find than heron- ries, it is beheved that few colonies were missed in the surveys. On the basis of the 6,397 nests counted, it is estimated that the total breeding Table 5. â Nest location of active Double-crested Cormorant colonies in the Canadian prairie provinces, 1967-1972 Number of nests Provinces Near lakes and ponds On lake islands In trees On the ground Alberta Saskatchewan Manitoba All three provinces 0 0 4 4 4 12 36 52 0 1 6 7 4 11 34 49 population of Double-crested Cormorants in
. The Canadian field-naturalist. 430 The Canadian Field-Naturalist Vol. 87 as a consequence are easier to find than heron- ries, it is beheved that few colonies were missed in the surveys. On the basis of the 6,397 nests counted, it is estimated that the total breeding Table 5. â Nest location of active Double-crested Cormorant colonies in the Canadian prairie provinces, 1967-1972 Number of nests Provinces Near lakes and ponds On lake islands In trees On the ground Alberta Saskatchewan Manitoba All three provinces 0 0 4 4 4 12 36 52 0 1 6 7 4 11 34 49 population of Double-crested Cormorants in the Canadian prairie provinces for the 1967- 1972 period consisted of 6,500 breeding pairs. The colonies averaged 114 nests and ranged from 2 to 1,010 nests (Table 6). Although the Manitoba colonies did not differ significantly in size from those in Alberta or Saskatchewan, the three largest colonies, with 645, 802, and 1,010 nests, were found in the Lake Manitoba - Lake Winnipegosis region (Figure 2). That region contained of the total breeding Table 6. â Comparison of the size of active Double- crested Cormorant colonies in the Canadian prairie provinces, 1967-1972 Provinces Number of colonies Mean colony size ± 95% confidence interval Range in colony size Alberta Saskatchewan Manitob? All three provinces 4 12 40 56 1 ± ± ± 2-232 4-434 3-1010 2-1010 population of Double-crested Cormorants in the area surveyed. The large majority of the cormorants nested on the ground on islands in lakes (Table 5). At three of the six places where they nested in trees, they were associated with Great Blue Herons. On treeless islands in lakes, cormorants always nested in association with gulls, either California Gulls {Larus californicus), Herring gulls, or Ring-billed Gulls and also frequently with White Pelicans, Common Terns or Caspian Terns. The breeding range of the Double-crested Cormorant in the Canadian prairie provinces is shown in Figure
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