Justification of Red List Category
This species has declined rapidly in parts of its range, but its status in other areas is poorly known. A number of factors are likely to be contributing to declines, including climate change, pollution and increasing human intrusion or hunting within breeding areas. It is currently considered Near Threatened; but further surveys are required in order to clarify the true magnitude of declines.
Using all data obtained recently and the current knowledge on Ivory’s gull biology in Russia, populations have been estimated at 1,000-1,500 breeding pairs on Franz-Josef Land (European Russia), 1,500-3,000 pairs on Severnaya Zemlya; and 1,000-2,500 pairs in the rest of the Kara Sea Islands (Central Asian Russia) (M. Gavrilo, unpubl. data). An estimated 1,000 pairs were recorded in northeast Canada (Hess 2004, Gilchrist and Mallory 2005, Mallory pers.comm. 2016), 900-2,000 pairs in Greenland between 2000 and 2012 and 800-1,500 pairs in Svalbard between 2001 and 2013 (BirdLife International 2015). Orr and Parsons (1982) recorded aerial estimates of possibly more than 35,000 individuals between Canada and Greenland in 1978-1979, while del Hoyo et al. (1996) estimated possibly 25,000 pairs (75,000 individuals). This gives a total of 58,100-77,200 individuals, rounded here to 58,000-78,000 individuals, roughly equivalent to 38,000-52,000 mature individuals.
Trends are difficult to estimate as colony size fluctuates from year to year, but sustained declines have been recorded in Canada. The European population is estimated to be fluctuating (BirdLife International 2015). Further information is required on long-term trends in other areas.
This species has a circumpolar distribution in the Arctic seas and pack-ice during the non-breeding season, while its breeding range is confined to the Arctic Atlantic sector. It breeds from Canadian Arctic Archipelago (to Canada) through Greenland (to Denmark), Svalbard (Svalbard and Jan Mayen Islands (to Norway), and islands of Franz-Josef Land, Severnaya Zemlya and offshore islands in the Kara Sea (to Russia). In Russia, there are 55 known sites where Ivory Gulls have bred or have been breeding until now (Gavrilo 2009). During the past 25 years, 38 breeding sites have been confirmed, eight historical sites have been abandoned and 10 remain unsurveyed. Using all data obtained recently and the current knowledge on the species' biology, populations have been estimated at 1,000-1,500 breeding pairs on Franz-Josef Land (European Russia), 1,500-3,000 pairs on Severnaya Zemlya and 1,000-2,500 pairs in the rest of the Kara Sea Islands (Central Asian Russia) (M. Gavrilo, unpubl. data). During the last five years, the numbers of breeding pairs varied greatly between seasons and also inter-annually. For example, the colony on Sedov Archipelago (Severnaya Zemlya) had 2,000 breeding pairs in 2006-2007, but has held between 100 and 1,000 pairs in previous years. Also, the total numbers for five of the monitored colonies dropped from a maximum of 2,720 breeding pairs observed during 1990s-2000s to 450 pairs in 2016. Overall, no large-scale survey covering most of the key colonies during the same single season has been performed after 2006 and, thus, further research is needed to assess the overall Russian population estimate and trend.Other populations include 1,000 individuals in northeast Canada (Hess 2004, Gilchrist and Mallory 2005, Mallory pers.comm. 2016), 900-2,000 pairs (equating to 2,700-6,000 individuals) in Greenland (BirdLife International 2015), and 800-1,500 pairs (equating to 2,400-4,500 individuals) in Svalbard (BirdLife International 2015). Extrapolations based on aerial estimates suggested >35,000 individuals between Canada and Greenland in 1978-1979 (Orr and Parsons 1982). The global population is perhaps best placed in the band 58,000-78,000 individuals.
Behaviour The species is migratory (Olsen and Larsson 2003). It breeds between late June and August (although most pairs do not lay until early-July). Most of the colonies in Canada, Greenland and Svalbard hold between 1-100 pairs (del Hoyo et al. 1996, Gavrilo et al. 2007, Volkov de Korte 2000). Breeding numbers in the same colony in any given season is a subject of great inter-annual fluctuations (up to 10 fold) depending on ice conditions (food availability) during the pre-breeding season (Gavrilo 2011a, Eamer et al. 2013). There is also inter annual alteration between different breeding sites (Bangjord et al. 1994, Mallory 2005, Robertson et al. 2007, MacDonald, 1976, Volokov and De Korte, 1996, 2000, Gavrilo 2011a, Spencer et al. 2012). It departs from the breeding grounds during August - first half of October, returning late-February to early-June (Malory et al. 2008, Olsen and Larsson 2003, Volkov and De Korte 2000, Gilg et al. 2010, Spencer et al. 2014). Most active migration occurs in November, with the first birds only arriving on the wintering grounds in December (Bering Sea, southeast Greenland, Davis Strait/Labrador Sea), and with birds from Greenland, Svalbard, and Russia arriving in sequence (Gilg et al. 2010). Most of the birds wintering in the Pacific are thought to originate from the largest Russian colonies, Kara Sea Islands and Severnaya Zemlya (Gilg et al. 2010). Between July-December, they may travel 50,000 km on average, and even more for individuals that move to the Pacific (Gilg et al. 2010). Outside of the breeding season the species is weakly gregarious, occurring singly or in flocks of up to 20 individuals (Snow and Perrins 1998) or up to 2,000 individuals in favourable feeding places (Renaud and McLaren 1982, Lydersen et al. 2014). Larger numbers also gather in the spring at Hooded Seal Crystophora cristata whelping sites, where they feed on carrion and discarded placentae (del Hoyo et al. 1996). The species also regularly follows Polar Bears Thalarctos maritimus to feed on scraps from their kill (del Hoyo et al. 1996). Habitat Breeding It breeds on the high Arctic islands north of the July 5oC isotherm (Snow and Perrins 1998). Twelve different habitats are described for the species (Gavrilo 2011b) which are grouped into two principal categories: i) relatively inaccessible coastal or inland (up to 50 km from the coast [Wright and Matthews 1980, Gilg et al. 2009]) rocky mountains and cliffs up to 750 m high (Frisch and Morgan, 1979) and ii) a variety of flat-ground habitats including plain polar deserts, gravel and sandy spits, stony plateau, small gravel/bare islands (del Hoyo et al. 1996, Snow and Perrins 1998, Gavrilo 2011b), or even icebergs (MacDonald 1962, Macpherson 1962, Boertmann et al. 2010, Nachtsheim et al. 2016) or grounded ice floes (Kristoffersen 1926) as well as abandoned wooden buildings and other human artefacts (Gavrilo 2011b). In general, spatial-territorial patterns of Ivory Gull breeding colonies distribution are affected by the terrestrial predation, mostly by Arctic Foxes Vulpes lagopus (Gavrilo 2011b, 2012). Non-breeding Outside of the breeding season it strongly associates with sea ice (del Hoyo et al. 1996, Gilg et al. 2010, Spencer et al. 2014) with preference for the marginal pack-ice zone. Gulls wintering in Davis Strait were found to persistently use ice areas with predictable and valuable food resources provided by remains of breeding and polar bear kills at the whelping patches of Hooded Seals (Spencer et al. 2016). The timing of formation and recession and extent of sea ice is suggested to play a large role in their distribution and migratory timing (Spencer et al. 2014). Diet Its diet consists predominantly of fish, crustaceans, molluscs, and carrion (e.g. seal placentae) (del Hoyo et al. 1996, Mallory et al. 2008, Karnovsky et al. 2009). The species is supposed to occupy upper trophic levels during the entire annual cycle, making it vulnerable to accumulation of toxic substances (Spencer et al. 2014). It feeds mostly by hovering and contact dipping in open leads in ice-filled waters or at the glacier fronts, walking along ice-floe edges and along the sandy beaches, or scavenging on marine mammal remains (Divoky 1976, Renaud and McLaren 1982, Mallory et al. 2008, Karnovsky et al. 2009, Lydersen et al. 2014, Gavrilo pers. comm.). Breeding site The nest is constructed of mosses and available vascular plants, straw and other debris on a snow-free area of broad rock ledges on steep, inaccessible coastal or inland cliffs up to 300 m high; on gravel, sand or clay ground; broken ice-fields and bare, level shorelines with low rocks; or on ledges, logs or roofs of abandoned buildings (del Hoyo et al. 1996, Snow and Perrins 1998, Gavrilo 2011a,b, Mallory et al. 2008, Volkov and de Korte 2000), avoiding areas with developed tundra vegetation (Gavrilo 2011b).
The loss of sea ice due to climate change represents a significant threat to the Ivory Gull as it is reliant on sea ice for breeding and hunting, selecting areas with 40-80% sea ice cover to forage. Decreasing sea ice has been linked to declines in Canada (Gilchrist and Mallory 2005) and changes to sea ice is decreasing the area of overlap with polar bears and seals, which they scavenge from, and is likely to lead to increased competition (Hamilton et al. 2017). Decreasing sea ice has been linked to declines in Canada (Gilchrist and Mallory 2005), as well as more generally across its range (Joiris 2017). Industrial diamond and gold mining in Canada (Bordeur Peninsula of Baffin Island, Severnaya Zemlya Archipelago) is likely causing habitat degradation and disturbance to breeding colonies (Gilchrist et al. 2008).
This species feeds high up in the trophic chain and is therefore vulnerable to bioaccumulation (Braune et al. 2006). With pollution accumulating in Arctic waters from diffuse sources, the exact sources of pollutants are unknown. The species' reliance on seal and whale blubber makes it particularly vulnerable to heavy metal contamination (Tucker and Heath 1994, Spencer et al. 2014). Trace heavy metals have been recorded, such as silver, arsenic, cadmium and lead (Braune et al. 2006, 2007, Miljeteig et al. 2009, Lucia et al. 2015), as well as high levels of pesticides, including organochlorinated pesticides (OCPs), DDT and polychlorinated biphenyls (PCBs) (Lucia et al. 2016). The levels of OCPs, polychlorinated biphenyls PCBs and mercury in Ivory Gulls are among the highest ever reported in Arctic seabirds (Braune et al. 2006, Miljeteig et al. 2009, Lucia et al. 2015). Yet, this is not thought to be at high enough concentrations to cause direct mortality. There is a threat from synergistic and additive effects, which are likely to having a sub-lethal effect, shown in other bird species to affect parental behaviour, endocrine distribution and neurological functions, as well as potentially causing reproductive disruptions (Miljeteig et al. 2012, Lucia et al. 2016). Mercury levels are some of the highest reported in Arctic sea birds, and egg concentrations of industrial contaminants exceed published thresholds known to disrupt reproductive success of avian species (Lucia et al. 2015). The concentration of methyl mercury in feathers of Canadian birds increased by a factor of 45 during 1877-2007 (Bond et al. 2015). High levels of selenium may offer some protection against mercury concentrations, but could also damage gulls (Lucia et al. 2016). Chronic oil pollution is suspected. Although there are no records of oiled Ivory Gulls, they would not be expected to reach land or be recorded due to their ecology. Given impact on other, similar species at risk such as Little Auk Alle alle and Thick-billed Murre Uria Iomvia, Ivory Gulls are likely highly to be at risk (Gilchrist et al. 2008).
The Ivory Gull has traditionally been hunted in Canada and Greenland and this is thought to have had an effect on their population (Stenhouse et al. 2004a). They have since become fully protected by law in Canada and Greenland (Stenhouse 2004) and, likely as a result of this, shooting is less common. Reports from Russia shows that hunting and egg collection seems to not have a major impact on the population (Gilchrist et al. 2008).
Conservation Actions Underway
Bern Convention Annex II. In Russia, it was listed in the Red Data Book of the U.S.S.R. (1984) and is currently registered as a Category 3 (Rare) species in the Red Data Book of the Russian Federation. As a result, the species is listed in regional Red Data Books along its breeding range in Russia (Gilchrist et al. 2008). However, there are currently no specific conservation measures in action for this species (Varty and Tanner 2009). A Norwegian-Russian project satellite tagged 31 individuals in 2007/2008 to assess movements at breeding grounds and their dispersal ability (Gilg et al. 2009).
Text account compilers
Martin, R., Moreno, R., Palmer-Newton, A., Stuart, A., Wheatley, H., Ashpole, J, Derhé, M., Butchart, S., Ekstrom, J., Fisher, S., Harding, M., Malpas, L., Calvert, R.
Stenhouse, I., Anderson, O., Miljeteig, C., Strom, H., Gavrilo, M., Volkov, A.
BirdLife International (2020) Species factsheet: Pagophila eburnea. Downloaded from http://www.birdlife.org on 07/08/2020. Recommended citation for factsheets for more than one species: BirdLife International (2020) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 07/08/2020.