VU
Red-legged Kittiwake Rissa brevirostris



Justification

Justification of Red List Category
This species underwent a rapid historical decline, but there is evidence that suggests that the population has now recovered, and potentially stabilised. It is precautionarily listed as Vulnerable.

Population justification

The Pribilof Islands account for >82% of the breeding population, with an estimated 235,624 breeding birds at St. George Island (per Goyert et al. 2017), 1,400 birds at St. Paul Island, and 172 at Otter Island (Thomson et al. 2014). The estimate for St. George is derived from a nest census conducted in 1995, while the estimates for St. Paul and Otter islands were taken from the most recent (2014) direct count of all attending birds conducted by the Alaska Maritime National Wildlife Refuge. The Commander Islands contain the only known Red-leggged Kittiwake colonies outside of the United States. These islands contain approximately 32,300 breeding birds (Vyatkin and Artyukhin 1994, del Hoyo et al. 1996, Artukhin 1999), which is approximately 14% of the breeding population. The colonies on Bering Island support by far the largest portion of the breeding birds of the Commander Islands, with an estimated 30,600 breeding birds in 1993 (Vyatkin and Artyukhin 1994). Recent counts for Bering Island and the other colonies in the Commander Islands group are not available. In the Aleutian Islands, Buldir Island (and its associated offshore rocks [Outer and Middle rocks]) is the largest colony with an estimated 8,605 breeding birds (per Goyert et al. 2017). Bogoslof Island and nearby Fire Island have a combined total of approximately 900 birds (Byrd et al. 2001). The remaining small colonies in the Aleutian Islands at Amak, Unalga, Koniuji and Chagulak islands contain fewer than 20 birds each (Byrd et al. 1997, 2004) and combined with Bogoslof Island account for <1% of the population. Overall, the population size in Alaska has been estimated at 247,300 breeding adults (Goyert et al. 2017), along with the population size of 32,300 in the Commander Islands, Russia. This gives a global population size estimate of 279,600 mature individuals, placed here in the range 100,000-499,999 mature individuals.

Trend justification
From the mid-1970s to mid-1990s, the known population declined by >40%. Most of this decline was on the Pribilof Island of St. George, where a precipitous (>50%) decline in breeding numbers occurred (Byrd and Williams 1993). The decline on St. George continued through the early 1990s, but subsequently has shown recovery (Byrd et al. 2008, Jason and Romano 2017). The small population on St. Paul Island declined by >80% from the mid-1970s through 2008 (Thomson et al. 2014), though since 2008, the population appears to have stabilised (M. Romano in litt. 2016). There is some evidence of a slight decline on the Commander Islands, but no counts are available prior to the late 1980s and it is unclear whether this was a trend or just interannual fluctuations (Byrd et al. 1997). No recent trend information is available for any of the Commander Islands. Of the remaining small colonies (all <5% of the population) the number of breeding birds at Buldir Island may have increased by as much as 55% between 1992 and 2014, and the number of breeding birds may have increased at Bogoslof Island in the mid-1990s (Byrd et al. 1997). Therefore, based on this evidence the decline over the past 3 generations (c.39 years) likely no longer meets the threshold for Vulnerable. Goyert et al. (2017), however, state that there have been recent declines in the species. With this uncertainty, the past and ongoing population reduction is very tentatively retained in the range 30-49% over 3 generations, though with further evidence of population trends, this precautionary assessment will require revision.

Distribution and population

Red-legged Kittiwake Rissa brevirostris occurs throughout the Bering Sea, and ranges across the North Pacific Ocean (including the Northern Gulf of Alaska) and the Sea of Okhotsk (USGS-ASC 2015). Vagrants have been noted along the Pacific Coast of Japan and along the West coast of the United States (Byrd and Williams 1993, Cole et al. 2006, Brazil 2009).
Nearly the entire global population breeds in the Bering Sea, on the Pribilof (St. Paul, St. George and Otter), Bogoslof (Bogoslof and Fire) and Buldir (Buldir, Outer Rock, Middle Rock) islands, U.S.A., and the Commander Islands (Arij Kamen, Toporkov, Bering and Mednyi), Russia (Byrd and Williams 1993, Byrd et al. 1997). In addition, smaller colonies on Unalga, Koniuji, Amak, and Chagulak islands (Aleutians, U.S.A.) were discovered during the 1990s and early 2000s (Byrd et al. 2004, Gibson and Byrd 2007).
Although their at-sea distribution is poorly studied, recent tracking efforts have shed new light into the at-sea habitat use of the species. Chick-rearing birds GPS-tracked from St. George Island forage to the southwest of the island in ocean waters (>1,000 m), with occasional trips over the Bering Sea shelf (Kokubun et al. 2015). Geolocation-tracking from St. George Island has revealed that the majority of birds disperse after breeding to the northern Bering Sea (Orben et al. 2015). Hot spots of non-breeding distribution in the Bering Sea occur along the Russian coast in the Gulf of Anadyr and the Karaginsky Gulf (Orben et al. 2015). Birds also winter along the Kuril Islands in the Sea of Okhotsk, and in the western subarctic gyre (Orben et al. 2015, Orben et al. unpubl. data).

Ecology

This species nests on remote oceanic islands in the Bering Sea. Nesting colonies occur on ledges of vertical sea cliffs up to 300 m high (Hickey and Craighead 1977). The species nests in dense aggregations often in the vicinity of other cliff nesting species, including the congeneric Black-legged Kittiwake (Rissa tridactyla). It forages in surface waters within the top 0.5 m and feeds on small fish (e.g. lampfish, juvenile walleye pollock and other gadids), squid and marine invertebrates by pursuit diving (Byrd and Williams 1993). Birds arrive at nesting colonies in April and leave around September (Byrd and Williams 1993, Orben et al. 2015).

Threats

Being restricted to a range within 10 degrees of latitude, the species is vulnerable to the impacts of changing ice distribution and sea surface temperature. An investigation into the foraging habits of Red-legged Kittiwakes on St. George Island found that they fed almost exclusively on lipid-rich myctophid fish during the reproductive period (Kokubun et al. 2015), although there is evidence that they are also able to feed on neritic prey (Hunt et al. in Orben et al. 2014). Myctophid fish are not widely commercially fished and are protected by law in the West Coast Exclusive Economic Zone (Federal Register 2016), which includes some of of the Red-Legged Kittiwake’s non-breeding range. As a result of this, the Red-legged Kittiwake is likely to be less affected by fisheries than other piscivorous seabirds in its range during breeding and likely also during other parts of the year. This limited diet does, however, put them at great risk from changes in prey abundance and distribution due to the effects of climate change. Changes in distribution of prey fish has already been attributed to a lack of lipids in the diet of kittiwake, with experimental studies showing that a lipid-poor diet during development leads to higher levels of stress hormones (Kitaysky et al. 2001, 2006), growth retardation and impaired cognitive ability (Kitaysky et al. 2006). This is backed up by modelling indicating a link between warmer surface temperatures and lower productivity up to 2 years later, likely due to lower reproductive success of new breeders raised during the period of low food and worse winter survival rates of adults, which have had to increase foraging effort to provision young (Kitaysky et al. 2006). Later ice retreat dates are also related with lower productivity 2 years later (Zador et al. 2013), likely for similar reasons. However, the rate of the declines observed at the global level in the species is uncertain. In Alaska, the St. Paul populations remain badly depleted, while those on St. George have recovered to a large extent (Byrd et al. 2008).

Although islands remain rat-free and a rat prevention programme is still in place, rats still pose a potential threat from boats arriving from mainland, rat-infested ports (Byrd and Williams 1993). Further human effects include subsistence offtake in Pribilofs, which could be causing decline; however, this is estimated under 250 birds collected annually on St Paul and St George (Byrd et al. 2008) described as 'trivial' and unlikely to affect the population.

Conservation actions

Conservation Actions Underway
It is a protected species in both the USA and Russia. All known Red-legged Kittiwake colonies in the U.S.A. are protected as part of the Alaska Maritime National Wildlife Refuge, administered by the U.S. Fish and Wildlife Service. All colonies within the Commander Islands occur within the Commander Islands Nature and Biosphere Reserve. A rat prevention programme, conducted by the U.S. Fish and Wildlife Service in partnership with the Tribal Governments of St. Paul and St. George, is underway in the Pribilof Islands (Byrd and Williams 1993).

Conservation Actions Proposed
Monitor breeding populations throughout the range to assess population trends, and continue and expand monitoring of vital demographic rates (e.g. productivity, adult survival, juvenile recruitment) in order to refine population models. Characterise the diet of Red-legged Kittiwakes at multiple colonies. Investigate the link between ocean/climate conditions and the availability of forage species at the major colonies. Assess the efficacy of rat prevention measures at breeding colonies and develop and maintain infrastructure to respond to potential rat introductions (via shipwreck etc.) at remote breeding sites. Continue tracking studies and expand to additional colonies (e.g. Buldir, Bering, and Bogoslof islands) to characterize winter distribution and foraging distribution during the breeding season. Assess the impact of commercial fishing, and if warranted establish the proposed buffer zone around the Pribilof Islands in which trawl fishing would be prohibited (Lensink 1984).

Identification

35-39 cm. Small gull. Adults mostly white, but dark grey upperwing and back. Black tips to outer primaries. Scarlet legs. Short bill and steep forehead give distinctive profile. Juvenile and first winter birds have more black on outer primaries and primary coverts, extensive white on inner primaries and secondaries. Similar spp. Black-legged Kittiwake R. tridactyla is lighter grey on upperwing and back, has longer bill and black legs. However, R. tridactyla can very rarely have reddish-orange legs. Immature R. tridactyla has carpal bar and tail-band.

Acknowledgements

Text account compilers
Stuart, A., Symes, A., Taylor, J., Westrip, J., Butchart, S., Benstead, P., Gilroy, J., Martin, R., Moreno, R., Ashpole, J, Palmer-Newton, A., Pilgrim, J.

Contributors
Romano, M., Orben, R., Renner, H., Artukhin, Y., Williams, J., Drew, G.


Recommended citation
BirdLife International (2021) Species factsheet: Rissa brevirostris. Downloaded from http://www.birdlife.org on 24/10/2021. Recommended citation for factsheets for more than one species: BirdLife International (2021) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 24/10/2021.