Distribution patterns of wintering sea ducks in relation to the North Atlantic Oscillation and local environmental characteristics

Abstract

Twelve species of North American sea ducks (Tribe Mergini) winter off the eastern coast of the United States and Canada. Yet, despite their seasonal proximity to urbanized areas in this region, there is limited information on patterns of wintering sea duck habitat use. It is difficult to gather information on sea ducks because of the relative inaccessibility of their offshore locations, their high degree of mobility, and their aggregated distributions. To characterize environmental conditions that affect wintering distributions, as well as their geographic ranges, we analyzed count data on five species of sea ducks (black scoters Melanitta nigra americana, surf scoters M. perspicillata, white-winged scoters M. fusca, common eiders Somateria mollissima, and long-tailed ducks Clangula hyemalis) that were collected during the Atlantic Flyway Sea Duck Survey for ten years starting in the early 1990s. We modeled count data for each species within ten-nautical-mile linear survey segments using a zero-inflated negative binomial model that included four local-scale habitat covariates (sea surface temperature, mean bottom depth, maximum bottom slope, and a variable to indicate if the segment was in a bay or not), one broad-scale covariate (the North Atlantic Oscillation), and a temporal correlation component. Our results indicate that species distributions have strong latitudinal gradients and consistency in local habitat use. The North Atlantic Oscillation was the only environmental covariate that had a significant (but variable) effect on the expected count for all five species, suggesting that broad-scale climatic conditions may be directly or indirectly important to the distributions of wintering sea ducks. Our results provide critical information on species-habitat associations, elucidate the complicated relationship between the North Atlantic Oscillation, sea surface temperature, and local sea duck abundances, and should be useful in assessing the impacts of climate change on seabirds.

Survival and local recruitment are driven by environmental carry-over effects from the wintering area in a migratory seabird

“…In several bird species, associations of the NAOI with vital rates have already been found (e.g. Forchhammer et al 1998;Grosbois and Thompson 2005;Crespin et al 2006;Descamps et al 2010;Zipkin et al 2010).…”

Temporal aggregation of migration counts can improve accuracy and precision of trends

“…A negative binomial distribution of counts is often assumed when variance is larger than the mean, and a zero-inflation parameter can model excess zero-observation counts that arise from true absence or nondetection given presence (Zipkin et al 2010, Ross et al 2012. Importantly, the ability to model the hierarchical structure of errors among hourly, daily, and annual counts, and to acknowledge and model temporal autocorrelation of counts, can result in more realistic estimates of precision that better reflect the true variability in the data (Ross et al 2012).…”

The early birds and the rest: do first nesters represent the entire colony?

“…Like other seaducks (Mergini), common eider spring arrival responded to local weather parameters, ice cover, the North Atlantic Oscillation (NAO) index and fertilizer release Jónsson et al 2009;Love et al 2010;Zipkin et al 2010;Laursen and Møller 2014). In northwest Iceland, spring icecover generally is absent but females arrived later following warm winters with strong westerly winds (positive NAO values; Jónsson et al 2009), whereas females in southwest Iceland nested earlier following milder winters (D'Alba et al 2010).…”