Seabirds
K.J. Kuletz1 and N.J. Karnovsky2
1U.S. Fish and Wildlife Service, Anchorage, AK, USA
2Department of Biology, Pomona College, Claremont, CA, USA
November 11, 2012
Highlights
- In the Atlantic Arctic, Dovekies (Little Auks), the most abundant seabird species in the arctic, show flexibility in foraging behavior and diet that has allowed some breeding colonies to do well despite warming ocean currents that affect their prey.
- Two circumpolar species, the common murre and thick-billed murre, show long-term fluctuations in population trends at colonies in response to changes in SST (sea surface temperature). These population trends tend to be synchronous within ocean basins, but alternate between Pacific and Atlantic sectors.
- Seabirds can bring beneficial nutrients from their ocean foraging grounds to breeding sites on land, but they can also concentrate and increase deposition of harmful contaminants and mercury at inland sites.
A total of 64 marine bird species are considered 'Arctic' in that they breed in the Arctic, and additional species spend at least part of the year in Arctic waters. Of the 64 Arctic species, 20 are circumpolar, found in both the Atlantic and Pacific sectors, while 19 species breed solely in the Atlantic and 25 species solely in the Pacific (Petersen et al., in press). In the Pacific sector, Sigler et al. (2011), analyzed seabird distribution at sea and identified three major species clusters, with the north Bering Sea and Chukchi Sea birds forming one group and the central and southern Bering Sea regions another, while the Beaufort Sea birds formed a distinctly separate group. The north Bering-Chukchi region was dominated by planktivorous birds (Aethia auklets in the north Bering Sea and Puffinus shearwaters in the Chukchi Sea), whereas the Beaufort seabirds were primarily piscivorous and circumpolar in distribution.
Over the past few decades the Arctic has experienced significant warming. In response to these warming trends, seabirds have shown shifts in their phenology, diets, physiology, foraging behavior, and survival rates. In the Atlantic sector there has been increase in the flow of warmer, more saline water in the West Spitsbergen Current into the Greenland Sea and into the Arctic Ocean (Piechura and Walczowski 2009), which affects plankton and therefore the diets of seabirds that feed on them (Kwasniewski et al., 2009). See the Ocean essay for further information about temperature and volume flux of Atlantic Water in the Greenland Sea and Fram Strait. Seabirds that breed in the Arctic face additional challenges during the non-breeding season. For example, using geolocators, Frederiksen et al. (2012) found that black-legged kittiwakes throughout the Arctic spend winters further south in regions where they may interact with fisheries or encounter oil spills.
Dovekies (Alle alle, also known as the Little Auk; Fig. 3.1), the most abundant seabird species in the Atlantic Arctic, and possibly in the World, are planktivores that nest on rocky slopes. From 1963 to 2008, dovekies showed a trend of earlier breeding and median hatch date became 4.5±2.1 days earlier. This is likely due to earlier nest site availability because of earlier snow melt (Moe et al. 2009). In contrast, the piscivorous black-legged kittiwakes (Rissa tridactyla) have shown a slight trend towards later breeding, which is likely related to delays or decreases in the availability of their fish prey due to warmer sea surface temperatures (SST) and loss of sea ice (Moe et al. 2009).
In the Arctic, copepods are a key prey in seabird food chains. In the Atlantic sector, increases in the flow of warm, Atlantic-derived water into the Greenland Sea have led to an increase in abundance of a smaller, low-lipid copepod, Calanus finmarchicus, instead of larger Arctic species (C. glacialis and C. hyperboreus) (Scott et al. 2000). While dovekies feed primarily on the large Arctic copepods (Karnovsky et al., 2003, 2010), in years with high inflow of Atlantic-derived water, they feed their chicks more of the smaller copepod species (Moline et al., 2010). Inter-colony comparisons of dovekie behavior found that dovekies make longer foraging trips when feeding in the warmer, Atlantic-derived water, where they must feed on the small copepod species, whereas at colonies where larger, high-lipid copepods are available, they spend less time searching for prey and make fewer deep dives (Welcker et al., 2009). For additional information on Atlantic Water in the Greenland Sea (Fram Strait) see the Ocean essay.
For dovekies, foraging conditions influence body mass and over winter survival of adult birds (Harding et al., 2011). However, despite variation in foraging conditions, dovekies have been able to maintain high reproductive success throughout the Greenland Sea (Jakubas et al., 2011; Jakubas and Wojczulanis-Jakubas, in press; Karnovsky et al., 2003, 2010; Gremillet et al., 2012; Harding et al., 2011). Continued warming, however, could result in extinction of colonies exposed to warmer Atlantic-derived water with sub-optimal prey (Karnovsky et al., 2010).
A much rarer arctic seabird that breeds in the Atlantic sector, the ivory gull (Pagophila eburnea), has declined by an estimated 80-90% over the past 20 years (Gilchrist and Mallory, 2005). This small gull nests in isolated nunataks (rocky outcrops among glacial icefields). Because the declines appeared to be occurring throughout Canada and in different breeding habitats, Gilchrist and Mallory (2005) suggest that the causes of decline are related to factors associated with migration or over-wintering conditions. As with many Arctic seabird species, lack of monitoring makes it difficult to determine population trends or the factors influencing them (Petersen et al., 2008).
There have been few long-term studies at seabird colonies in the Pacific Arctic, with the exception of two sites monitored by the Alaska Maritime National Wildlife Refuge - the Cape Lisburne colony (mainland Alaska in the eastern Chukchi Sea) and Bluff colony (mainland Alaska in the northern Bering Sea, Norton Sound). Two species have been monitored at these sites since the late 1970s, the black-legged kittiwake and the common murre (Uria aalge). Between 1975 and 2009, kittiwake numbers have increased overall at Cape Lisburne, but their reproductive success has declined since 2004 (Dragoo et al., 2012). These contrasting trends suggest immigration to the region by prospecting birds, i.e., birds from elsewhere looking for a new place to nest. At the Bluff colony, both kittiwakes and murres have shown stable population trends, but their mean hatching dates have been earlier than the long-term (1975-2009) mean (Dragoo et al., 2012); the earlier hatch dates suggest an adaptation to earlier prey availability by both seabird species.
Two species of murres, the common murre and thick-billed murre (U. lomvia) are widespread and relatively abundant throughout the Arctic; consequently, they have been identified as a key species to monitor by the Circumpolar Seabird Group of CAFF (Petersen et al., 2008). In a pan-Arctic study of both murre species, data from 32 common and 21 thick-billed murre colonies were used to examine population trends and the potential influence of SST (Irons et al., 2008). The more Arctic thick-billed murre colonies increased in size when SST warmed slightly, whereas the more temperate common murre colonies increased with moderate cooling, but both species had negative trends when SST changes were extreme, regardless of direction. These patterns showed synchronous fluctuations relative to SST, with changes in trends being synchronous within ocean basins and opposite between the two basins (Pacific and Atlantic). These population trends might reflect changes in the prey base, but this remains to be determined. For more information about SST, see the Ocean essay.
Seabird tissues and eggs have become useful tools to monitor a wide variety of contaminants that can impact the birds themselves and serve as indicators of environmental health (e.g., Vander Pol and Becker, 2007). One example is the use of murre eggs to study atmospheric deposition of mercury in the Arctic. Variations in the isotopic composition of mercury in murre eggs (a reflection of the female bird's diet in spring) show that deposition increased with latitude and was negatively correlated with sea-ice cover (Point et al., 2011). Loss of sea-ice cover could accelerate the amount of biologically accessible methylmercury throughout the food chain (Point et al., 2011). By foraging in the ocean and returning to land-based colonies, seabirds transport beneficial nutrients to land, but they may also be responsible for transporting contaminants to inland lakes and soils. Blais et al. (2005) found that Arctic ponds near large colonies of northern fulmars (Fulmarus glacialis) had higher levels of persistent organic pollutants and mercury, and suggested that contaminants in seabirds could be an indicator of ecosystem health and are also a direct concern to indigenous peoples relying on traditional foods.
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