Have Lesser Scaup, Aythya affinis, Reproductive Rates Declined in Parkland Manitoba?

Résumé

Long-term surveys indicate that the scaup populations have declined over the past 20 years, and that this is probably the result of decreases in Lesser Scaup (Aythya affinis) rather than Greater Scaup (Aythya marila) numbers. To identify factors possibly related to the decline, we estimated demographic parameters for a local population of Lesser Scaup at Erickson, Manitoba, that was well studied before declines occurred and compared these estimates to historic rates. On average, nests were initiated later than in the past, and recent estimates of nesting success and duckling survival were lower than historical estimates. Breeding-season survival of adult females was estimated as 72.6%, with most (83%) mortality occurring during nesting. Current estimates of demographic rates at Erickson are too low to maintain a stable local population, and suppressed reproductive rates might be the proximate cause of the local population decline.