Aleutian Tern (Onychoprion aleuticus, formerly Sterna aleutica): uplist to Vulnerable or Endangered?

This discussion was first published as part of the 2014 Red List update, but remains open for comment to enable reassessment in 2015.

Current species factsheet for Aleutian Tern:

Aleutian Tern Onychoprion aleuticus is currently listed as Least Concern on the basis that it was not thought to approach the thresholds for Vulnerable under any of the IUCN Red List criteria.

It breeds entirely in the north Pacific Ocean on the coasts of Sakhalin and Kamchatka, Russia, on the Bering and Pacific coasts of Alaska (USA) and on the Aleutian Islands (USA). It is strongly migratory, and although the wintering range is poorly known it is believed to lie off Indonesia and Malaysia.

Published population estimates for Alaska range from 9,000 to 12,000 birds, and estimates for Russia range from 7,200 to 13,000, although they are based on data that are more than 20 years old (H. Renner in litt. 2013). Wetlands International estimate a total population of 17,000-20,000 individuals, including 9,500 birds in Alaska (Wetlands International 2014), based on data from the U.S. Fish and Wildlife Service (2006).

A 2013 status assessment by the U.S. Fish and Wildlife Service compiled new data on Alaskan colonies (including surveying more than half of the known active colonies in 2013) and suggested that the population at surveyed colonies had declined by 79% since 1995, with perhaps fewer than 5,000 individuals in Alaska as a whole. This number is not 79% lower than the published population estimate owing to the discovery of previously undocumented colonies. However, colonies with data points both before and after 1995 have declined 79%.  In addition, few new colonies (3) have been discovered since 1995, while 56% of colonies active prior to 1995 (24) have been reduced to zero (H. Renner in litt. 2013).

Surveys on the Kodiak Archipelago in 2008-2010 visited 86% of known colonies (324 out of 377) and recorded only 326 Aleutian Terns at 11 colonies (Corcoran 2012). Four of the five largest colonies that supported from 240-3,000 individuals in the 1970s now are used intermittently and at reduced numbers with counts ranging from 22-120 terns. Although the species is difficult to monitor since colonies often shift from year to year, given the few sightings in the region in the past decade it is reasonable to conclude that this species has declined rather than relocated within the Kodiak Archipelago (Corcoran 2012).

Data available for Aleutian Tern colony sizes are not optimal for a variety of reasons, including variable survey methodology as well as extreme variation in attendance, common breeding failure, and occasional colony movement.  Nonetheless, there appears to be sufficient evidence of a dramatic decline in Alaska.

Data on the Russian breeding population are currently missing from this picture. Personal communications with Russian ornithologists indicate the species is stable in Russia (H. Renner in litt. 2013), but no published data are available.

No single main driver of declines has been identified but several factors including habitat modification, predation, egg harvesting and disturbance by humans likely play a substantial role in population change at local scales, and may have a cumulative impact at the population level. Eggs and chicks are reportedly preyed on by introduced species such as arctic (Alopex lagopus) and red (Vulpes vulpes) foxes, Norway rats (Rattus norvegicus), and domestic dogs. Natural predators include mink (Mustela vison), bears (Ursus spp.), and a wide variety of other bird species. Some chicks may also be killed by Arctic Terns (U.S. Fish and Wildlife Service 2006). There is limited information regarding response to predation, but Aleutian Terns are not as aggressive as Arctic Terns and are very sensitive to disturbance at colonies. Individuals frequently hover high over the colony if disturbed by humans. They will dive at avian predators, but often rely on the more aggressive Arctic Terns to chase intruders away.

If evidence points towards a decline approaching 30% (typically 25-29%) over three generations, estimated by BirdLife to be c.33 years, either in the past, in the future, or over a period including both the past and the future, then the species may be eligible for uplisting to Near Threatened under the A criterion. A decline of 30-49% over 33 years would qualify the species for uplisting to Vulnerable, and a decline of 50-79% over the past 33 years, predicted to occur in the next 33 years, or over a specified period of time including both the past and the future, would warrant uplisting to Endangered.

Data from the Russian population and comments on the likely global population trend  are requested.


Corcoran, R.M. 2012. Aleutian tern counts from seabird colony and nearshore marine bird surveys in the Kodiak Archipelago, Alaska 1975-2012 Unpubl. Refuge Report 01-12. U.S. Fish and Wildlife Service, Kodiak National Wildlife Refuge, Kodiak, Alaska

U.S. Fish and Wildlife Service 2006. Alaska Seabird Information Series: Aleutian Tern Onychoprion aleutica

Wetlands International (2014). “Waterbird Population Estimates” . Retrieved from on Friday 14 Mar 2014

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9 Responses to Aleutian Tern (Onychoprion aleuticus, formerly Sterna aleutica): uplist to Vulnerable or Endangered?

  1. Andy Symes says:

    Preliminary proposals

    Based on available information, our preliminary proposal for the 2014 Red List is to pend the decision on Aleutian Tern Sterna aleutica and keep this discussion open until early 2015, while leaving the current Red List category unchanged in the 2014 update.

    There is now a period for further comments until the final deadline of 16 May, after which recommended categorisations will be put forward to IUCN.

    The final Red List category will be published on the BirdLife and IUCN websites in mid-2014, following further checking of information relevant to the assessment by both BirdLife and IUCN.

  2. Yat-tung Yu says:

    Discussion of this species has been raised within the EAAFP Seabird Working Group through emails and updated information of this species in E and SE Asia was also requested. Only a few information was received as single or two at Sunda Strait, Indonesia, in August and September. Apparently, only Hong Kong has regular records of this species in this region since 1992 (but through regular birdwatching activities rather than standard survey). This species is a passage migrant of Hong Kong (April to early June, early August to mid-October). The highest single count at Hong Kong was 865 individuals on May 1999 and numbers varied from less than 10 (e.g. in 2002 and 2004) to several hundreds individuals (e.g. in 2009 and 2010). Therefore, no clear trend was shown from the records in Hong Kong.

  3. Joe Taylor says:

    Recommended categorisations to be put forward to IUCN

    Following further review, there has been no change to our preliminary proposal to pend the decision on Aleutian Tern Sterna aleutica and keep this discussion open until early 2015, while leaving the current Red List category unchanged in the 2014 update.

  4. Heather Renner says:

    Data from 90 known colonies in Russia have been shared with me by Yuri Artukhin, Russian Academy of Science. We are in the process of determining whether they can be included in our trend model, and will have results to share in the few months. Clearly the majority of the world’s population of Aleutian terns now nest in the Russian Far East, especially the northern end of Sakhalin Island which may host 2/3 of the world’s population. 1/3 to 1/4 of the colonies in Russia are only documented as “presence” and many others only have one quantitative estimate (so no trend is available) – however Sakhalin Island and the Koryak Uplands seem to be stable or increasing. I will share more data when it is available.

  5. Christoph Zockler says:

    I have been monitoring a Aleutian Tern colony near Anadyr since 2000, when there were around 20 pairs. This declined over the years to 11 in 2005 and none in 2011 and 2012. We also noted a decline in numbers further north, where we suspected still smaller colonies.

    Colonies on Kamchatka from Central Kamchatka to North Kamchatka hold good numbers in 2008 and 2009 respectively. Together with Yuri Gerrassimov we summarised the 2008 findings from the Ust Kamchatsk area for 2008, where we found also many mixed colonies relatively far inland at remote bogs (see Gerrassimov et al 2012: Gerassimov, Yu.N., E.E. Syroechkovskiy, E.G. Lappo, C. Zöckler, J.R. McCallum, R.V. Bukhalova (2012): To the knowledge of Bird Fauna of The Kamchatka River Mouth. Ornithologiya 37: 5-26

    In 2009 w erecorded several colonies previously unknown in the Ossora region. Several of those were close to local communities and regularly visited by egg collectors, who unfortunately were not selective and also did not leav one egg for the birds to continue to breed. A colony at Karaga south of Ossora this way had hardly any success.

    Unfirtaunetly, as Heather already says, most of these places are very remote and very little monitoring takes places so trend information is lacking completely apart from the Anadyr site. My sense is however that the species has declined quite strongly and a monitoring plan needs to be developed. The species is at least near threatened but most likely VU. however more monitoring in Kamchatka and Sakhalin is requested.

    I have more detailed information.

  6. Heather Renner says:

    A manuscript is now in press in Marine Ornithology describing the status and trends of Aleutian terns in Alaska and Russia. I am happy to send the manuscript to anybody requesting it. Here is the abstract:

    We compiled survey data on 202 colonies throughout Alaska and Russia to assess the current status and colony sizes of Aleutian Terns and to evaluate changes in recent decades. We fit a Poisson generalized linear mixed model to all available counts of Alaskan colonies since 1960, excluding colonies with less than a 6-year temporal spread in counts. Russian data were not included in the trend model due to our inability to resolve dates on a number of counts. We estimate that numbers at known colonies in Alaska have declined 8.1% annually since 1960 or 92.9% over three generations (33 years; 95% CI =83.3-97%) with large colonies experiencing greater declines than small colonies. Trends at known colonies within discrete geographic regions of Alaska (Aleutian Islands, Bering Sea, Chukchi Sea, Gulf of Alaska, and Kodiak Island) were consistently negative. The most recent counts of all known Alaskan colonies sum to 5,529 birds. This number should be considered a rough minimal estimate because it does not take into account that some colonies have not been surveyed in recent years and their size may have changed, and that the surveys that were conducted were neither systematic nor inclusive of all potential habitats. In Russia, the sum of the most recent count of all colonies was 25,602 individuals, indicating that Russia may host approximately 80% of the world’s population. Numbers in some regions in Russia appear to have increased substantially in recent decades, especially on Sakhalin Island and the southern coast of the Koryak Highland. We have no data to identify any population-level stressor that could explain the apparent reduction in numbers in Alaska. However, predation, egging and other anthropogenic disturbances, and degrading habitat may cause population change at local levels. If this overall pattern cannot be explained by other possible but unlikely factors, (e.g., establishment of large colonies in new locations within Alaska, major shifts between Alaska and Russia), then the observed trends in Alaska populations are, indeed, alarming. Therefore, we urge close monitoring of known colonies within Alaska, studies of dispersal, establishment of management practices to insulate colonies from human disturbance, and more concerted efforts among Alaska and Russian partners.

    • Yu Yat-tung says:

      Dear Heather,

      I am very much interesting to read the manuscript. Would you mind to send me a copy (my email address:

      Thank you very much

      Yat-tung Yu

      Research Manager,
      Hong Kong Bird Watching Society

      • Yu Yat-tung says:

        Dear Heather,

        Thank you very much. The manuscript is received from my side. I just wanted to reply you directly through email but your server has blocked my reply.

        Best regards,

  7. Andy Symes (BirdLife) says:

    Preliminary proposals

    Based on available information, our preliminary proposal for the 2015 Red List would be to pend the decision on Aleutian Tern and keep this discussion open until 2016, while leaving the current Red List category unchanged in the 2015 update.

    There is now a period for further comments until the final deadline of 31 August, after which recommended categorisations will be put forward to IUCN.

    The final Red List categories will be published on the BirdLife website in late October and on the IUCN website in November, following further checking of information relevant to the assessments by both BirdLife and IUCN.

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