Population ecology of breeding Pacific common eiders on the Yukon‐Kuskokwim Delta, Alaska

• Published in: Wildlife Monographs
• Main Authors: Wilson, Heather M., Flint, Paul L., Powell, Abby N., Grand, J. Barry, Moran, Christine L.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2012
• Subjects: Pacific; Yukon; Kuskokwim; Somateria mollissima; Alaska
• Online Access: http://dx.doi.org/10.1002/wmon.8; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fwmon.8; https://onlinelibrary.wiley.com/doi/full/10.1002/wmon.8

Abstract Populations of Pacific common eiders ( Somateria mollissima v‐nigrum ) on the Yukon‐Kuskokwim Delta (YKD) in western Alaska declined by 50–90% from 1957 to 1992 and then stabilized at reduced numbers from the early 1990s to the present. We investigated the underlying processes affecting their population dynamics by collection and analysis of demographic data from Pacific common eiders at 3 sites on the YKD (1991–2004) for 29 site‐years. We examined variation in components of reproduction, tested hypotheses about the influence of specific ecological factors on life‐history variables, and investigated their relative contributions to local population dynamics. Reproductive output was low and variable, both within and among individuals, whereas apparent survival of adult females was high and relatively invariant (0.89 ± 0.005). All reproductive parameters varied across study sites and years. Clutch initiation dates ranged from 4 May to 28 June, with peak (modal) initiation occurring on 26 May. Females at an island study site consistently initiated clutches 3–5 days earlier in each year than those on 2 mainland sites. Population variance in nest initiation date was negatively related to the peak, suggesting increased synchrony in years of delayed initiation. On average, total clutch size (laid) ranged from 4.8 to 6.6 eggs, and declined with date of nest initiation. After accounting for partial predation and non‐viability of eggs, average clutch size at hatch ranged from 2.0 to 5.8 eggs. Within seasons, daily survival probability (DSP) of nests was lowest during egg‐laying and late‐initiation dates. Estimated nest survival varied considerably across sites and years (mean = 0.55, range: 0.06–0.92), but process variance in nest survival was relatively low (0.02, CI: 0.01–0.05), indicating that most variance was likely attributed to sampling error. We found evidence that observer effects may have reduced overall nest survival by 0.0–0.36 across site‐years. Study sites with lower sample sizes and more frequent ...