Nest Success and Duckling Survival of Greater Scaup, Aythya marila, at Grassy Island, New Brunswick

Nesting biology and duckling survival of Greater Scaup (Aythya marila) at Grassy Island on the Saint John River in southern New Brunswick were compared between 1995 and 1996. Grassy Island in New Brunswick is an area that is notably removed from other scaup breeding areas, being located farther south from main breeding areas in North America. The Mayfield estimates of nest success were 61% and 21% in 1995 and 1996, respectively. Mean daily survival rates were 0.99 in 1995 and 0.96 in 1996 and were significantly different (t = 4.86, P < 0.001). Duckling survival was estimated to range from 38 to 54% in 1995, and was 8% in 1996. The lower breeding success in 1996 may have been due to factors associated with decreased temperatures and increased precipitation, but the fact that the breeding location is atypical to other Greater Scaup breeding areas should not be overlooked.

Nesting Biology of Mallards in West-central Illinois

The number of Mallards (Anas platyrhynchos) breeding in Illinois and eastern North America has increased in recent decades; however, few studies have investigated the nesting biology of Mallards outside primary production areas. Therefore, we radiomarked resident female Mallards (n = 148) in west-central Illinois during 1998–2003 to assess nesting parameters and evaluate recruitment. Mean initiation date for first nests ranged from 22 April to 6 May, and the majority (75%) of nests were initiated by 20 May. Therefore, the majority of nests were predicted to hatch by 24 June. The nesting season averaged 88 days (range: 77–103 days). The proportion of unsuccessful females that renested ranged from 50.0–85.7%, and adults were more likely to renest (75.0%) than yearlings (48.0%). Nest success ranged from 9.8–33.3% and was 19.6% overall; hen success was 28.3%. Initial brood size was 8.2 ± 0.3 ducklings, but brood size declined to 3.0 ± 0.6 ducklings by 17 days posthatch. Brood survival to 20 days was 0.759 ± 0.081, and 20-day duckling survival was 0.413 ± 0.035. Female survival during spring-summer ranged from 0.546–1.00 and averaged 0.710 ± 0.096. Likewise, estimated Mallard recruitment varied annually (range: 0.302–0.672 female ducklings/female). Assuming constant female and duckling survival, we estimated that a recruitment rate of 0.613 female ducklings/adult female was necessary to maintain a stable Mallard breeding population in west-central Illinois. Estimated Mallard reproduction and recruitment was similar to that observed in other areas of North America. Nest success and hen success approached or exceeded estimated thresholds for population stability in most years; however, hen success averaged over the study period was insufficient for local population maintenance and growth. Female survival was comparable to that observed in other studies but may have limited population growth in some years. Duckling survival was sufficient for population maintenance. Management designed to enhance hen success and brood habitat may augment Mallard recruitment in west-central Illinois.