Habitat use by trumpeter swans in the Grande Prairie region of Alberta
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AbstractTrumpeter swans breeding in Alaska, in the Tri-state region of Idaho, Montana and Wyoming, and in the Grande Prairie region of Alberta have survived the destruction of habitat and the shooting which threatened this species with extinction. Although the ecology of the swans in Alaska and the Tri-state region has been documented, the swans breeding in the Grande Prairie region had not been studied in detail. This study examined the use of habitat by swans breeding in the Grande Prairie region and investigated whether the number of lakes which provide suitable habitat might limit the number of swans in this population. In the Grande Prairie region, the mean width of zones of emergent vegetation, and the total edge length of portions of these zones which were greater than 40 m wide, were greater in lakes occupied by breeding swans in 1979 than in historically unoccupied lakes. Because most swans nested in emergent vegetation, these analyses suggested that breeding swans select lakes on the basis of the availability of potential nest sites. Although the abundance of submerged macrophytes did not appear to influence the selection of lakes by breeding swans, adult swans with cygnets used portions of lakes where the biomass of submerged macrophytes was high. Chara spp., Lemna trisulca, Potamogeton richardsonii, P. strictofolius, and P. zosteriformis may be important foods of these swans. All lakes which appeared to provide suitable habitat for breeding swans were not occupied each year from 1973-1980. This appears to suggest that the number of swans breeding in the Grande Prairie region is not limited by the number of these lakes. Swans bred on some lakes which were exposed to agricultural and related human activity in fewer years from 1973-1980 than they on lakes which were isolated from these potential disturbances. This implies that the use of some lakes by the swans may be inhibited by agricultural activity. However, those swans that bred on lakes which were exposed to agricultural and related human activity exhibited clutch sizes, brood sizes, hatching success, and cygnet survival that did not differ significantly from those of swans exposed to low levels of these activities. Incubation behavior did not differ significantly between swans exposed to these differential levels of activity. Therefore, the reproductive success of the swans in this region does not appear to be affected by the differing intensity of agricultural activity near the lakes.
Bibliography: p. 138-146.