Nesting of northern pintails in Alberta: laying date, clutch size, and renesting

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Abstract
Nesting of northern pintails was studied in southern Alberta where breeding densities are high. Adults nested earlier and laid larger clutches than did yearlings in the wild. Captive pintails nested earlier, laid larger clutches, and appeared to renest more readily than did wild birds. Food may limit each of these parameters in the wild. The reproductive output of female pintails nesting in high densities in southern Alberta appears to be lower than that of birds breeding at Delta, Manitoba, because of reduced clutch size and lower renesting rate. Clutch size was strongly correlated with laying date but the laying of larger clutches by adults in the wild (and by captive birds relative to wild birds) was not simply a consequence of earlier nesting. A number of proximate causes suggested to explain the seasonal decline in clutch size (hen age, renesting, declining food resources, and decreased body reserves) were rejected. Whatever the mechanism through which laying date influences clutch size, the ultimate reason for this phenomenon may be a seasonally declining survival rate of young which has selected for reduced reproductive effort later in the breeding season. Captive pintails fed a 14% or 29% protein diet after laying their first clutches did not differ in frequency of renesting, clutch size, or renest interval.