ARCTIC SEABIRDS: DIVERSITY, POPULATIONS, TRENDS, AND …peregrinefund.org/subsites/conference-gyr/proceedings/201-Gaston.pdf · Great Skua Stercorarius skua XXX 5 LC Pomarine Skua

SEABIRDS HAVE PROVIDED A SOURCE OF FOOD forArctic peoples throughout their history andmost major seabird colonies within the rangeof the post-Pleistocene Inuit expansion areassociated with archaeological sites that attestto significant harvest and storage of seabirds(Freuchen and Salmonsen 1958, Nelson 1983).Some Arctic communities are heavily depend-ent on seabird harvesting (e.g., Ivujivik, Que-bec, Gaston et al. 1985; Siorapaluk, Greenland,Malaurie 1985). Early European explorationsin Arctic and sub-Arctic waters also madeextensive use of seabirds for food (e.g., HenryHudson’s crew, Prickett 1611). Consequently,these birds have been of interest to people fora very long time.

Census of Arctic seabird colonies began in the1930s in Greenland (Salomonsen 1950) andRussia (Uspenski 1956), the 1950s in easternCanadian Arctic (Tuck 1961), the 1960s inSpitzbergen (Norderhaug et al. 1977, Mehlumand Bakken 1994), and the 1970s in the north-ern Bering and Chukchi seas (www.seabirds. net/maps/dev/north-pacific.php?v=14). Subse-quent monitoring was sporadic in most regionsuntil the 1980s, but has become more regularsince then (CAFF Seabird Working Group,unpubl.). However, many breeding sites areextremely remote, in places where navigationis challenging and support for aircraft very dis-tant. Consequently, although we have a goodpicture of distributions, and some idea of pop-

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ARCTIC SEABIRDS: DIVERSITY, POPULATIONS, TRENDS, AND CAUSES

ANTHONY J. GASTON

Wildlife Research Division, Environment Canada, National Wildlife Research Centre, Ottawa K1A 0H3, Canada.

E-mail: [email protected]

ABSTRACT.—Populations and trends of Arctic seabirds have been the subject of substantialresearch since the 1930s in Europe and Greenland and since the 1950s in North America. Themarine waters of the Arctic support 44 species of seabirds comprising 20 genera. There are fourendemic monotypic genera and an additional 25 species for which the bulk of the population isconfined to Arctic and sub-Arctic regions. Most Arctic seabirds have large populations, with onlytwo species comprising less than 100,000 individuals and many species numbering in the millions.Population trends for several widespread Arctic species have been negative in recent decades.Conversely, some sub-Arctic species are spreading northwards. Climate change with consequentchanges in competition and predation, and intensifying development in the north, increasinglythreaten Arctic seabirds. Changes in ice conditions are likely to have far-reaching and potentiallyirreversible results. Received 22 February 2011, accepted 26 May 2011.

GASTON, A. J. 2011. Arctic seabirds: Diversity, populations, trends, and causes. Pages 147–160 inR. T. Watson, T. J. Cade, M. Fuller, G. Hunt, and E. Potapov (Eds.). Gyrfalcons and Ptarmigan in aChanging World, Volume I. The Peregrine Fund, Boise, Idaho, USA. http://dx.doi.org/10.4080/gpcw.2011.0201

Key words: Seabirds, diversity, population size, population trends, Arctic.

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ulation sizes, our information on populationtrends is rather fragmentary and localised andour knowledge of causes behind change inpopulations is even less substantial (Gaston etal. 2009). This paper attempts to review whatwe do know of seabird population size and sta-tus, understanding that there is considerableuncertainty especially about population trends.

SPECIES RICHNESS AND DISTRIBUTION

Forty-four species of seabirds breed within theArctic (Table 1), 23 in the High Arctic, 41 inthe Low Arctic. They belong to 20 genera, therichest in species being Larus (10 spp.), Gavia(5 spp.) and Stercorarius (4 spp.). Six generaare monotypic. The majority are members ofthe order Charadriiformes, 34 species, includ-ing four endemic genera, all monotypic: LittleAuk (Alle alle), Ivory Gull (Pagophilaeburnea), Sabine’s Gull (Xema sabini), andRoss’s Gull (Rhodostethia rosea). Fifteenspecies are circumpolar in their distribution,occurring in Canada, Alaska and over most ofthe Russian Arctic. There are two ‘bi-polar’genera, found at high latitudes in both hemi-spheres–the fulmars (Fulmarus), and the skuasand jaegers (Stercorarius), the former likelyoriginating in the southern hemisphere (Voous1949), the latter in the northern hemisphere(Furness 1987). All four species of Stercorar-ius found in the northern hemisphere areendemic to the Arctic and sub-Arctic, as is thesingle fulmarine petrel, all the loons, terns andauks and five species of Larus gulls.

Overall diversity is highest in the low-Arcticof the Pacific Basin (Chukchi and Bering seasand adjacent coasts) where 28 species occur inthe Alaskan low-Arctic (including islandssouth to 60º N) and 26 species on the Asianside. Other biodiversity hotspots occur in WestGreenland (24 spp.), eastern Canadian Arctic(Nunavut, northern Quebec and Labrador, 22spp.), and Iceland (22 spp. excluding the sub-Arctic/boreal species found only on the southcoast).

Several taxa have been elevated to species sta-tus only recently and were previously consid-ered sub-species. These splits mainly involvedistinguishing North American and Eurasianpopulations: Arctic/Pacific Loons (Gavia arc-tica/pacifica), American/European HerringGull (Larus smithsonianus/argentatus). Thelarge white-headed gulls of the genus Larusare divided into several poorly differentiatedand mostly allopatric species in northern Asiaand on the west coast of North America. Muchof their diversity was regarded as infra-specificuntil recently (cf. Vaurie 1965, Olsen and Lars-son 2003).

The distributions of many species of Arcticmarine birds were poorly known until the latterhalf of the twentieth century. In addition, manyspecies are long-lived and conservative in theirbreeding site adherence, making them slow toalter their breeding range. Consequently, wehave few data on which to assess trends inrange extent among Arctic seabirds. No strictlyArctic species has become extinct during his-toric times, although three sub-Arctic species,Spectacled Cormorant (Phalacrocorax per-spicillatus) (Commander Islands), LabradorDuck (Camptorhynchus labradorius)(Labrador) and Great Auk (Pinguinus impen-nis) (Newfoundland and Iceland) were huntedto extinction by Europeans in the 19th Century(Fuller 2000). Ivory Gull and Ross’s Gull arelisted by IUCN/Birdlife International as threat-ened or endangered at a world scale.

There is some evidence for the recent north-ward spread of predominantly temperate orlow-Arctic species: Ancient Murrelet (Synthli-boramphus antiquus) in the Bering Sea (Gas-ton and Shoji 2010), Horned Puffin(Fratercula corniculata) in the Beaufort Sea(Moline et al. 2008), Mew (Common) Gull(Larus canus) in Iceland (Petersen andThorstensen 2004), Black-headed Gull(Chroicocephalus ridibundus) in Labrador(Chaulk et al. 2004), Great Black-backed Gull(Larus marinus) and Razorbill (Alca torda) inHudson Bay (Gaston and Woo 2008). At the

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same time there is evidence of a retreat for atleast one high-Arctic species, with the range ofthe Ivory Gull contracting in northernNunavut, with most colonies on northern Baf-fin Island and eastern Devon Island desertedwhile numbers have remained stable farthernorth on central Ellesmere Island (Environ-ment Canada 2010). Southern colonies are alsodecreasing in Greenland (Gilg et al. 2009). Thepopulation trend in Russia is unclear (Gilchristet al. 2008) but some colonies at their westernextremity in the Barents Sea region have beendeserted (Gavrilo 2010). The population ofKittlitz’s Murrelet (Brachyramphus brevi-rostris), a species associated with tidewaterglaciers in the low- and sub-Arctic of theNorth Pacific, is declining in its core breedingrange in south central Alaska and perhaps else-where (Kuletz et al. 2003, Stenhouse et al.2008). Similar changes have been noted bylocal people:

“I have started to notice birds which Iused to only see on TV, little birds whichhave multi-coloured bills, that fly homewith multiple cod in their beaks and thatburrow into the soil. I think these arethe Atlantic puffins [Fratercula arctica],which are located some distance southmigrating north due to the disappear-ance of the ice cover during the summermonths” (Pijamin: Elders Conferenceon Climate Change 2001).

With little evidence for range changes, it is dif-ficult to ascribe causes. The spread of Razor-bill in Hudson Bay has been linked to anincrease in sandlance Ammodytes spp., perhapsrelated to diminishing ice cover (Gaston andWoo 2008). Reduced ice cover also is likely tobe involved in the arrival of Horned Puffin inthe Beaufort Sea. The association of Kittlitz’sMurrelet with tidewater glaciers makes itlikely that recent declines are caused by theretreat of many Alaskan coastal glaciers (Sten-house et al. 2008). In the longer run, changesin ice cover must affect the distribution of ice-

associated species such as Ross’s and Ivorygulls and Thick-billed Murre (Uria lomvia).

POPULATION SIZES AND DENSITIES

Most species have populations numbering inthe hundreds of thousands and only two arebelieved to number less than 100,000 breedingindividuals: Ivory Gull and Thayer’s Gull(Larus thayeri) (Table 1). Among high-Arcticspecialists, the Ivory Gull has decreased pre-cipitously in Canada (by 80% since the 1980s),has decreased in Greenland, and shows rangecontraction in the northern Barents Sea. In allcases the southern parts of the range seem tobe more affected than northern parts (Gilchristand Mallory 2005, Gilchrist et al. 2005, Gilg etal. 2009, Environment Canada 2010). Of theother two exclusively high-Arctic species,population size for Thayer’s Gull, which isconfined to eastern and central parts of theCanadian high-Arctic and northwest Green-land, is very poorly known, but certainly num-bers less than 100,000 (AJG, M.L. Malloryand H.G. Gilchrist unpubl.). The Little Auk,although well-distributed in small pocketsaround the Arctic Ocean, is numerically con-centrated into a single location in northwestGreenland (Crimson Cliffs and adjacent coastsof Thule District) where the population,although difficult to count, is believed togreatly exceed ten million birds (Renaud et al.1982). Censusing such an aggregation isalmost impossible and no information is avail-able on trends. Some small colonies in south-ern Greenland and in Iceland have disappearedsince the 1930s (Nettleship and Evans 1985).

Thick-billed and Common Murres (Uriaaalge)are among the most abundant seabirds inthe Northern Hemisphere with both speciesexceeding 10 million adults (Gaston and Jones1998). Both have circumpolar distributions.The more northern species, U. lomvia, occursmostly in Arctic waters, where it constitutes ahigher proportion of seabird biomass than anyother species. Both species of murre haveshown regional population changes over the

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Loons Gaviidae

Red-throated Loon Gavia stellata X X X X X X X X 6 LC

Black-throated Loon Gavia arctica X X X X 6 LC

Pacific Loon Gavia pacifica X X X X 6 LC

Great Northern Loon Gavia immer X X X X X 6 LC

Yellow-billed Loon Gavia adamsii X X X X X X 5 LC

Petrels Procellariidae

Northern Fulmar Fulmarus glacialis X X X X X X X 8 LC

Cormorants Phalacrocoracidae

Great Cormorant Phalacrocorax carbo X X 6 LC

European Shag Phalacrocorax aristotelis X X 6 LC

Pelagic Cormorant Phalacrocorax pelagicus X X 6 LC

Gannets Sulidae

Northern Gannet Morus bassanus X X 6 LC

Jaegers/Skuas Stercorariidae

Great Skua Stercorarius skua X X X 5 LC

Pomarine Skua Stercorarius pomarinus X X X X X X 6 LC

Parasitic Jaeger Stercorarius parasiticus X X X X X X X X 7 LC

Long-tailed Jaeger Stercorarius longicaudus X X X X X X X 7 LC

Table 1. Seabird species occurring in the circumpolar Arctic, by region, with global populationestimate (orders of magnitude and IUCN status).

Ala

ska

NW

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Nu

nav

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Qu

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L

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Gre

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Icel

and

Sva

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Sib

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Table 1. (continued)

Gulls and Terns Laridae

Black-headed Gull Chroicocephalus ridibundus X 8 LC

Mew Gull Larus canus X X X X X 7 LC

G. Black-backed Larus marinus X X X X X 6 LCGull

Glaucous Gull Larus hyperboreus X X X X X X X X 6 LC

Iceland Gull Larus glaucoides X X 6 LC

Thayer's Gull Larus thayeri X X 4 LC

Amer. Herring Gull Larus smithsonianus X X 6 LC

Lesser Black-backed Larus fuscus X X X X 6 LCGull

Herring Gull Larus argentatus X X 7 LC

Vega Gull Larus vegae X 6 LC

Slaty-backed Gull Larus schistisagus X X 6

Ivory Gull Pagophila eburnea X X X X 4 NT

Ross's Gull Rhodostethia rosea X X X 5 LC

Sabine's Gull Xema sabini X X X X X X 6 LC

Black-leg. Kittiwake Rissa tridactyla X X X X X X X 8 LC

Arctic Tern Sterna paradisaea X X X X X X X X 7 LC

Aleutian Tern Onychoprion aleuticus X 5 LC

Auks Alcidae

Little Auk Alle alle X X X X X X X 8 LC

Common Murre Uria aalge X X X X X X 7 LC

Thick-billed Murre Uria lomvia X X X X X X X 8 LC

Razorbill Alca torda X X X X 6 LC

Black Guillemot Cepphus grylle X X X X X X X 7 LC

Pigeon Guillemot Cepphus columba X 6 LC

Kittlitz's Murrelet Brachyrhamphus brevirostris X X 5 CE

Parakeet Auklet Aethia psittacula X X 7 LC

Crested Auklet Aethia cristatella X X 7 LC

Least Auklet Aethia pusilla X X 7 LC

Atlantic Puffin Fratercula arctica X X X X X 8 LC

Horned Puffin Fratercula corniculata X X 7 LC

Tufted Puffin Fratercula cirrhata X X 7 LC

1(orders of magnitude, breeding individuals)

Ala

ska

NW

T

Nu

nav

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Qu

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L

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Gre

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Icel

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Sva

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past three decades, with trends in the NorthPacific and Northwest Atlantic generally pos-itive or stable when trends in the EuropeanArctic were negative and vice versa (Irons etal. 2008). By combining population trend datafrom around the Arctic with information on seasurface temperature changes (SST) anddecadal-scale climate-ocean oscillations, Ironset al. (2008) showed that population growthwas most often positive where conditionsremained relatively stable and negative whenchange, either colder or warmer, was large.This result suggests that not only the directionbut the magnitude of change may be importantin determining biological outcomes of climate.Trends in different regions switched directionwith regime shifts. However, U. lomvia popu-lations have declined in all regions except theCanadian eastern Arctic since the 1970s,whereas no single global trend can be identi-fied for U. aalge.

The population of Thick-billed Murres in Cen-tral West Greenland is much depressed com-pared to numbers in the early nineteenthcentury, as a result of heavy harvesting ofadults at colonies (Evans and Kampp 1991), aswell as drownings in gill-net fisheries (Tull etal. 1972) and shows no sign of recovery, withthe population south of Thule District remain-ing at <20% of historical levels (Kampp et al.1994, Merkel et al. 2007, F. Merkel pers.comm. 2010). Numbers in East Greenland,although small, have also declined. Similarly,numbers in Novaya Zemlya are considerablylower than in the early twentieth century whenthe population numbered several million birds.Currently, there are thought to be in the regionof one million breeders (Bakken andPokrovskaya 2000). In Spitzbergen, numbersof Thick-billed Murres were thought to be sta-ble up to the 1990s, but have since decreased,especially in the southern part of the archipel-ago (CAFF Circumpolar Seabird WorkingGroup, unpubl.)

In Iceland, numbers of Thick-billed Murresdecreased at 7% per year between 1983–1985

and 2005–2008, while numbers of CommonMurres decreased abruptly between 1999–2005 after modest increases earlier (Gardars-son 2006). Northern Fulmar (Fulmarusglacialis), Black-legged Kittiwake (Rissa tri-dactyla) and Razorbill also decreased,although some small colonies increased (Gar-darsson et al. 2009).

CAUSES OF POPULATION CHANGES

The causes of population and range changescan rarely be confidently attributed to a singlesource. The decline of Ivory Gulls in the Cana-dian Arctic illustrates a case where severalpotential contributory causes can be identified:heavy hunting of adults in Greenland (Sten-house et al. 2004), high levels of mercury ineggs (Braune et al. 2006) and changes in iceconditions associated with global warming(Environment Canada 2010). All may havecontributed to recent population decline. Onlywhere population declines are abrupt and asso-ciated with strong environmental signals, cancauses be confidently assigned. This was thecase for Common Murre populations in thesouthern Barents Sea in 1985–87 when num-bers fell by 80% in response to starvation fol-lowing the collapse of the Barents Sea Capelin(Mallotus villosus) stock (Anker-Nilssen et al.1997). The population subsequently recoveredto near its former level (Krasnov et al. 2007).Similarly, an 80% decrease in Lesser Black-backed Gulls in northern Norway coincidedwith a collapse in the stock of spring spawningHerring (Clupea harengus) (Bustnes et al.2010).

Most changes in demography and populationstatus of Arctic seabirds that have been linkedwith climate changes have, to date, beenascribed to causes operating through the foodchain (Harris et al. 2005, Sandvik et al. 2005,Durant et al. 2004, 2006, Irons et al. 2008).However, a few cases where direct effects haveoccurred have been documented. Mallory et al.(2009) reported a wide range of weather-related mortalities at Arctic seabird colonies

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and suggested that some types of mortality,especially those associated with increases inextreme weather events, could create heaviermortality in the future. In northern HudsonBay in the late 1990s, a combination of warmsummer weather and earlier emergence bymosquitoes, leading to heavy blood-sucking,caused the death of some incubating Thick-billed Murres through a combination of dehy-dration and hyperthermia. In addition, somebirds left their eggs unattended for periods ofseveral hours, resulting in many losses topredatory gulls (Gaston et al. 2002). Theseeffects had not been recorded previously in 20years of observations. Changes in the timing ofsnow-cover and ice-melt affect the availabilityof breeding sites to crevice, scree and burrow-nesting species, such as puffins and Little Auks(Birkhead and Harris 1985). Such changes inaccessibility can result in altered interactionswith predators, as observed for AntarcticPetrels (Thalassoica antarctica) by vanFraneker et al. (2001).

Although both species of murre are currentlyabundant, many populations have been declin-ing for several decades (Johnsen et al. 2010).Problems facing murres include fisheries inter-actions, contaminants and oil spills and, insome parts of their range, hunting (especiallyof U. lomvia). For U. lomvia, changes in theextent and timing of sea-ice cover over the pastseveral decades are leading to changes in phe-nology and reproduction with adverse conse-quences for nestling growth (Gaston et al.2005). These changes seem likely to intensify.Levels of some contaminants, especially mer-cury, have increased in murre eggs in the NorthAmerican Arctic since the 1970s, althoughthey remain at sublethal levels (Braune et al.2001). If climate change leads to increasedshipping and oil and gas exploitation in Arcticwaters, the increased risk of spills would alsopose a potential hazard for murres, which areextremely susceptible to mortality from oilpollution (Wiese and Robertson 2004). In thelong-term, range contraction of U. lomvia inresponse to the retreat of Arctic sea ice appears

likely. Eventually it may be replaced by U.aalge and other more southern auks.

Substantial research has been carried out in theBarents Sea region and in the Canadian Arcticon concentrations and trends in contaminants,especially organohaline compounds and heavymetals (Braune et al. 2001, Letcher et al.2010). Very high levels of mercury (Braune etal. 2006) and organohaline compounds (Mil-jeteig et al. 2009) have been found in the eggsof Ivory Gulls from Canada and Svalbard andhigh organohaline concentrations occur also inGlaucous Gulls (Larus hyperboreus) fromSvalbard (Bustnes et al. 2003, 2004), perhapscausing mortality in some cases (Gabrielsen etal. 1995, Sagerup et al. 2009). These speciesscavenge marine mammal carcasses, puttingthem high up the food chain and hence subjectto high biomagnification effects. They mayalso frequent garbage dumps around humanpopulation centres. Levels of contaminants inother species generally do not approach thoselikely to impact populations (Gabrielsen 2007,Letcher et al. 2010), except in the case ofpoint-source pollution resulting from industrialsites (e.g., Kuzyk et al. 2003).

Changes in the timing of seasonal events forhigh-latitude marine birds have been identifiedfor many southern hemisphere species (Croxallet al. 2002, Rolland et al. 2010), as well assome Arctic seabird populations (Gaston et al.2005, Byrd et al. 2008a,b, Moe et al. 2009).For some Arctic species, reproductive successis inversely correlated with date of laying, e.g.,Little Auks (Moe at al. 2009), but this relation-ship may vary among geographical areas; it istrue for Thick-billed Murres breeding at PrinceLeopold Island, Nunavut, but not for the samespecies breeding in northern Hudson Bay(Gaston et al. 2005). The importance of timingof breeding in determining the dynamics ofArctic seabird populations is supported by acorrelation found between colony size and thetiming of sea ice withdrawal in adjacent watersfor Thick-billed Murres in Greenland (Laidreet al. 2008).

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Mismatching of breeding initiation with theseasonal peak of food availability may be acommon phenomenon among seabirds con-fronted with rapidly changing seasonal timing(Bertram 2001, Wilhelm et al. 2008, Watanukiet al. 2009). It has been identified as a likelycause of reduced nestling growth for Thick-billed Murres in northern Hudson Bay (Gas-ton et al. 2009), as well as accounting forsome of the variation in reproductive successof Black-legged Kittiwakes and CommonMurres in sub-Arctic Alaska (Suryan et al.2006, Schultz et al. 2009) and Newfoundland(Wilhelm et al. 2008).

Changes in seabird diets, both from year toyear and over decades, have been reportedfrom many sites. Diet switching is likely afairly routine aspect of seabird biology (e.g.,Montevecchi and Myers 1995, 1997, Barrett2002). At Coats Island, northern Hudson Bay,Thick-billed Murres switched from feedingtheir chicks predominantly the ice-associatedArctic Cod (Boreogadus saida) to the moresub-Arctic Capelin in the mid-1990s (Gastonet al. 2003). The change was associated withan advance in the date of sea-ice clearance inthe region.

Not all prey are equally suitable, especially forrearing nestling birds, and some prey switchescan result in reduced productivity amongseabirds (Litzow et al. 2002, Wanless et al.2005, Gremillet et al. 2008). In the southwestBarents Sea in recent decades Herring hascome to dominate over Capelin as a foragefish. This change has coincided with a declinein numbers of breeding Back-legged Kitti-wakes (–8% per year after 1995). ApparentlyHerring is not as satisfactory as Capelin asfood for kittiwakes (Barrett 2007). At the Pri-bilof Islands, Sinclair et al. (2008) alsoobserved a reduction in the proportion ofCapelin in Black-legged Kittiwake and Thick-billed Murre diets between the 1980s and2000s, while changes in the zooplankton dietof Least Auklets (Aethia pusilla) was alsoobserved over the same period (Springer et al.

2007, Sheffield Guy 2009). These changeswere associated with a warming of the adja-cent surface waters and a retreat of winter seaice. Similarly, in Iceland, the diet of mostseabirds switched from sandlance to otherfishes in the 2000s (Gardarsson 2006), achange also observed in boreal waters of theNorth Sea (Wanless et al. 2005). This dietchange was contemporary with declines inmost seabird populations.

Many seabirds are very conservative in theirbreeding sites, returning faithfully to largecolonies that, in some cases, have been in exis-tence for millennia (Gaston and Donaldson1996). If climate change alters environmentalconditions around such colonies it is unlikelythat a mass exodus will take place in search ofnew colony locations. There are examples oflarge colonies suffering repeated reproductivefailure over many years without any substan-tial emigration (e.g., Atlantic Puffins at Rost,Norway reared few chicks between 1969–1982, Anker-Nilssen and Rostad 1993). How-ever, parasites and predators may be moremobile in response to climate change and mayinitiate or expand their activities at new sites.Some examples of such expansions havealready been observed, with an increase in theincidence of tapeworms in alcids in Labradorand Greenland since the 1960s (Bin Muzaffar2009) and the appearance of the parasitic tick(Ixodes uriae) on murres in Svalbard after2000 (Coulson et al. 2009). The implicationsof these parasite range expansions are not yetclear but adverse consequences for the seabirdpopulations involved are possible.

Currently Golden Eagles (Aquila chrysaetos)and White-tailed Sea-eagles (Haliaeetus albi-cilla), both of which cause disruption to nest-ing seabirds, only reach the fringes of theArctic. Their northward spread could createproblems for gulls, murres and other open-nesting seabirds. Increasing predation of birdsand their nests by Polar Bears (Ursus marinus)has also been observed, probably as a result ofthe bears coming ashore earlier in the season

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(Rockwell and Gormezano 2009, Smith et al.2010). This could affect especially accessiblespecies such as Little Auks (Stempniewicz2007). Because of the potential for alternativeprey, it is extremely difficult to predict howseabird populations will respond to changes inpredator distributions.

CONCLUSIONS

The Arctic is an important area for marine birddiversity and endemism. Most Arctic seabirdpopulations for which information is availableover several decades have shown negativetrends in recent years. These trends are super-imposed on a situation where several impor-tant populations were substantially depressedby anthropogenic mortality, compared withnumbers in the first half of the twentieth cen-tury (especially Thick-billed Murres in Green-land and Novaya Zemlya).

Only a few instances are available whererecent trends can be traced to particular causesbut stressors include fisheries activities, pollu-tion, and climate change. The last, especiallyas manifested in changes in the timing of theopen water season, is affecting the timing ofseasonal events in marine ecosystems and thisis affecting the optimal timing of breeding,especially in low-Arctic areas. Changes in iceconditions, especially, are likely to have far-reaching and potentially irreversible conse-quences. These changes are also encouragingthe northward expansion of sub-Arctic species,although such changes in range are relativelysmall, as yet. Changes in the distributions ofpredators and parasites have also been notedand these may have important consequencesfor Arctic seabirds. Because of the number ofArctic endemic seabird taxa, the decline ofArctic marine birds presages a significant lossof global biodiversity.

ACKNOWLEDGMENTS

Thanks to the many students, contractors, col-laborators and volunteers who have assistedwith seabird research and monitoring in theCanadian Arctic. Our efforts would not havebeen successful without the financial andlogistic support of Natural Resources Canada(Polar Continental Shelf Program), theNunavut Research Institute, Indian and North-ern Affairs Canada (Northern ContaminantsProgram), and various branches of Environ-ment Canada (Canadian Wildlife Service andScience and Technology Branch). For informa-tion and advice on literature sources, I thankCarsten Egevang, Maria Gavrilov, ArnthorGardarsson, Grant Gilchrist, David Irons,Mark Mallory, Freydig Vigfúsdóttir, and mem-bers of the C-bird working group of CAFF.

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