Lesser Scaup Nest Success and Duckling Survival on the Yukon Flats, Alaska

Abstract

Over the last 20 years scaup numbers have declined, and these declines have been greatest in the northern boreal forests of Canada and Alaska where most lesser scaup (Aythya affinis) nest. We studied nest success and duckling survival of lesser scaup over 3 field seasons, 2001–2003, on the Yukon Flats National Wildlife Refuge in northeastern Alaska, USA. Daily survival rate (DSR) of nests on our study area across all 3 years was 0.943 (n = 177 nests, 95% CI: 0.930–0.954), corresponding to a nest success of only 12.3%, considerably lower than published estimates of an average nest success as high as 57% for lesser scaup in the northern boreal forest. With Mayfield logistic regression, we investigated effects on nest survival of year, clutch initiation date, and nesting habitat type (large wetlands >10 ha, small wetlands <10 ha, and wooded creeks). Neither year nor clutch initiation date influenced nest survival; however, the odds of nest success on large wetlands was 49% lower than on wooded creeks (odds ratio = 0.512, 95% CI = 0.286, 0.918). Based on the model that used only habitat type for estimation, DSR on large wetlands was 0.931 (corresponding nest success = 7.6%), DSR on small wetlands was 0.941 (nest success = 11.1%), and DSR on wooded creeks was 0.963 (nest success = 26.2%). To estimate duckling survival, we monitored 10 broods (n = 75 ducklings) over 3 field seasons by radiotagging hens at nest hatch. Most duckling mortality (94%) occurred in the first 10 days after hatch. Average duckling survival during 1–10 days was 0.321 (95% CI: 0.122–0.772), during 11–20 days was 0.996 (95% CI: 0.891–1.040), and during 21–30 days was 0.923 (95% CI: 0.769–1.041). Three of 10 hens moved all or part of their broods overland between nesting and brood‐rearing wetlands for distances of 0.3–1.6 km. Our estimates of lesser scaup nest success and duckling survival on the Yukon Flats were among the lowest ever reported for ducks nesting at northern latitudes, even though the study site was in pristine boreal forest. Estimating and comparing scaup demographic rates from different geographic areas can contribute to improved conservation. Given the scarcity of information on scaup nesting in the boreal forest, basic nesting parameters are important to those trying to model scaup population dynamics.

Reproductive Rates in Lesser Scaup (<i>Aythya affinis</i>) in Southwestern Manitoba: Another Look at the Data

“…However, at the Erickson breeding site, Koons and Rotella (2003) reported estimates of nest success (11%) and duckling survival (20%) during 1999-2000 to be low and similar to rates recorded for recent studies in boreal forest areas (Fournier and Hines 2001;Brook 2002;Corcoran et al 2007;Martin 2007). In southern Saskatchewan, in 1999-2000, Brook (2002 reported lower nest success (3%) and duckling survival (38% Dawson and Clark 1996) than at Yellowknife (14% and 61%, respectively).…”

“…For boreal breeding scaup, historical nutrient reserve data are sparse (body mass only; Trauger 1971) but lipid reserves of boreal females measured during [2003][2004] in northern Alberta and the Northwest Territories were much lower than historical values reported for females in northwestern Minnesota in 1986-1988and southwestern Manitoba in 1977-1980(Anteau and Afton 2004, 2009a; but see DeVink et al 2008c). Furthermore, recent studies have reported that some reproductive parameters, such as nest success, female survival, duckling and brood survival, and breeding probability, were low in boreal and parkland breeding sites, at rates that would be consistent with the SCH (Fournier and Hines 2001;Brook 2002;Koons and Rotella 2003;Corcoran et al 2007;Martin et al 2009). Afton and Anderson (2001) and Anteau and Afton (2009a) speculated that reduced food resources at nonbreeding areas would affect body condition and, hence, recruitment of northern boreal breeders more than southern prairie-parkland breeders because of the shorter time between arrival and egg-laying in the north.…”

“…During 1970During -1972, some females were marked with a coded plastic nasal saddle, so that broods were more readily identified (Sugden and Poston 1968). Brood surveys began during the first week of July and, because scaup females usually move their broods from smaller to larger (usually class 5) wetlands as they mature (Hammell 1973;Corcoran et al 2007), surveys were conducted mostly on class 4 and 5 wetlands until broods reached age class IIa (21-28 days of age). Greatest duckling losses and most brood movement occur before ducklings reach age class IIa (Hammell 1973;Afton 1983;Dawson and Clark 1996;Brook 2002;Corcoran et al 2007).…”

“…Brood surveys began during the first week of July and, because scaup females usually move their broods from smaller to larger (usually class 5) wetlands as they mature (Hammell 1973;Corcoran et al 2007), surveys were conducted mostly on class 4 and 5 wetlands until broods reached age class IIa (21-28 days of age). Greatest duckling losses and most brood movement occur before ducklings reach age class IIa (Hammell 1973;Afton 1983;Dawson and Clark 1996;Brook 2002;Corcoran et al 2007). Also, most brood-rearing females spend increasing amounts of time away from their broods after they reach age class IIa, and at that point ducklings often form groups on lakes making it difficult to distinguish individual broods (personal observations; Hines 1977;Afton 1984).…”

“…Neither of these studies published total brood loss or IIa broods/ pair values comparable to my study. Published estimates of total brood loss for scaup are few and limited to boreal scaup, but losses are high Corcoran et al 2007).…”