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Article Excerpt
(Received 1 July 2008; accepted in revised form 4 November 2008)
ABSTRACT. In more than 30 years of studies on marine birds in Arctic Canada, we have observed numerous instances of mortality of adults, eggs, and chicks that seem unusual when compared to known sources of mortality for seabirds breeding in temperate or tropical regions. The extreme cold weather and ice conditions of the Arctic might intuitively be expected to be a significant factor in mortality for these Arctic birds. While weather conditions led directly to seabird mortality, other factors, perhaps facilitated by typical Arctic climate features, caused more deaths. In this paper, we summarize mortality incidents that we have witnessed for nine species of Arctic marine birds, as a baseline against which future observations can be made. We also speculate on mechanisms by which climate change could increase mortality of breeding Arctic seabirds in the future.
Key words: Arctic, marine bird, mortality, predation, weather
RESUME. Dans le cadre d'etudes sur les oiseaux aquatiques qui se sont echelonnees sur plus de 30 ans dans l'Arctique canadien, nous avons observe de nombreuses incidences de mortalite chez les adultes, dans les oeufs et chez les oisillons, incidences qui semblent inhabituelles lorsqu'elles sont companies aux sources connues de mortalite des oiseaux de mer qui se reproduisent dans les regions temperees ou tropicales. Intuitivement, nous croyons que le temps froid extreme et le regime des glaces de l'Arctique peuvent representer un facteur de mortalite important chez ces oiseaux de l'Arctique. Bien que les conditions climatiques aient directement entraine la mort des oiseaux de mer, d'autres facteurs, qui sont peut-etre declenches par les caracteristiques climatiques typiques de l'Arctique, ont occasionne d'autres deces. Dans ce document, nous resumons les incidents de mortalite dont nous avons ete temoins pour neuf especes d'oiseaux aquatiques de l'Arctique comme point de reference en vue d'observations futures. Nous emettons egalement des hypotheses a propos des mecanismes dans le cadre desquels le changement climatique pourrait accroitre la mortalite des oiseaux de mer de l'Arctique en reproduction a l'avenir.
Mots cles: Arctique, oiseau aquatique, mortalite, predation, conditions meteorologiques
Traduit pour la revue Arctic par Nicole Giguere.
INTRODUCTION
Seabirds generally share traits of low annual reproductive output, delayed maturation, and high annual survival (Lack, 1968; Schreiber and Burger, 2002; Gaston, 2004). To date, seabird research has focused on issues that influence aspects of birth and fledging, including factors affecting reproductive effort, nest failure (i.e., egg and chick mortality), and annual reproductive success (e.g., Hamer et al., 2002; Schreiber, 2002; Frederiksen et al., 2006). Mortality of adult seabirds has also received much attention, but this topic is generally more difficult to study. Most previous publications have dealt with events outside the Arctic, especially fisheries bycatch (e.g., Tull et al., 1972; Melvin and Parrish, 2001; Mallory et al., 2006a; Rolland et al., 2008), oil spills (e.g., Piatt and Ford, 1996; Wiese et al., 2004), harvest (Hansen, 2002; Priest and Usher, 2004), and mass mortality events known as seabird "wrecks" (Warham, 1996; Gaston, 2004; Bugoni et al., 2007), die-offs that are often highly visible because numerous seabird carcasses wash ashore (Bourne, 1976; Hudson, 1985). Seabird wrecks are often linked to poor feeding conditions (usually storm-related) in winter and may kill thousands of birds (e.g., Schreiber, 2002; Anker-Nilssen et al., 2003; Gaston, 2004). Aside from these highly visible mortality events, much less is known about factors leading to other natural mortality of adult seabirds, even in the case of disease outbreaks (Friend et al., 2001).
In the Arctic, migration mortality of some marine birds has been documented, particularly for eider ducks (e.g., Barry, 1968). However, few studies have reported natural sources of mortality of adult seabirds during the Arctic breeding season, when weather conditions can be extreme and may intuitively be considered a major factor in bird mortality. Previous reports have often included brief and anecdotal evidence (e.g., Hatch and Nettleship, 1998; Gaston and Hipfner, 2000; Gilchrist, 2001; Butler and Buckley, 2002), but quantitative details of adult mortality are lacking.
In more than three decades of studies in the Canadian Arctic, we have observed numerous instances of seabird mortality during the breeding season, much of it from causes unlikely to occur at lower latitudes. Perhaps the most obvious environmental difference faced by seabirds in Arctic Canada compared to southern waters is the presence of cold, extreme weather through much of the year. Arctic sea-birds initiate nesting while the marine regions surrounding them may still be ice-covered. Ice occasionally persists into the chick-rearing period at some locations (Gaston et al., 2005; Mallory and Forbes, 2007). Moreover, temperatures at many colonies can be near or below 0[degrees]C through much of the season, and significant snowstorms can occur in any month, particularly in the High Arctic.
Given the paucity of documented and quantifiable adult mortality reported during the breeding season, we summarize published and unpublished data on mortality of adult seabirds (auks, petrels, gulls, eiders) breeding in the Canadian Arctic to provide a baseline against which future observations may be compared. Our focus was on natural mortality events that we considered "unusual," that is, mortality other than from expected predation (e.g., foxes at nests; Gaston et al., 1985). Because we were concerned with natural mortality, we also exclude a discussion of human harvest, although this is a significant mortality factor for some seabirds in the Canadian Arctic (Merkel, 2004; Wiese et al., 2004). Finally, we comment on unusual mortality of eggs and chicks to demonstrate how sources of mortality for these Arctic species may differ from those documented for seabirds nesting in temperate and tropical regions.
METHODS
The observations reported here have accrued during field research projects conducted during the May-to-August breeding season in selected years between 1975 and 2008. Opportunities to observe adult mortality during the breeding season occurred at 11 different seabird colonies (Fig. 1). Details of the years of observations and geomorphology of the sites are listed in Table 1. Observations at these colonies focused on six species, namely thick-billed murres (Uria lomvia), black guillemots (Cepphus grylle), northern fulmars (Fulmarus glacialis), black-legged kittiwakes (Rissa tridactyla), glaucous gulls (Larus hyperboreus), and common eiders (Somateria mollissima borealis), but we had occasional observations on other species during breeding (Tables 2, 3). Note also that we use the term "seabird" to include marine waterfowl (notably eiders). Our summary represents an estimated 1700 person-days of our own observations, plus records from a minimum 2000 days by our field staff (with camps of 2 12 people on each day, thereby representing an estimate of more than 7000 person-days).
[FIGURE 1 OMITTED]
TABLE 1. Details of colonies where observations were made. Numbers refer to Figure 1. Number Colony Lat/Long. Years Height and...
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