1.25 1.50 1.75 2.00 2.25 2.50 2.75 3.00 3.25 3.50 Index of prairie pond numbers (millions)
0.30 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25 Ratio north/south populations
Figure 19.7 Distribution and breeding success of Northern Pintails Anas acuta in relation to wetland conditions on the Canadian prairies. (a) Relationship between numbers of ponds and lakes on the prairies in May and the proportion of the total Pintail population found breeding north of the prairies, 1958-1968 (r = 0.91, P < 0.001) (b) Relationship between the proportion of the total Pintail population in northern areas and overall breeding success (r = -0.92, P < 0.001). Redrawn from Smith (1970).
the greatest proportions of Pintail occurred in northern breeding areas. Some similar findings were obtained for Mallard (Pospahala et al. 1974).
In general, these various patterns were supported by other ring recoveries, with diving ducks showing strong site-fidelity, and the dabbling ducks variable but generally much lower site-fidelity (Table 17.5; Johnson & Grier 1988). The Blue-winged Teal was extreme in various local studies, in that very few adults or young were found to return to the same nesting areas in successive years. The northward displacement of several species in drought years from the prairies to the tundra was also confirmed by ringing; it represented a substantial shift in the breeding sites of adults in successive years and between natal and breeding sites for yearlings.
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