The Arctic tern is considered a rare bird in many parts of its breeding range. However, assessing the true rarity of the Arctic tern is complex due to several factors.
Breeding Range and Population
The Arctic tern has a circumpolar breeding distribution, nesting in Arctic and subarctic regions around the northern hemisphere. Its breeding range includes northern parts of Europe, Asia, and North America. Current global population estimates for the Arctic tern range from 1 million to 3 million pairs.
Within its widespread breeding range, the Arctic tern nests in scattered colonies, rather than uniformly across the landscape. Colonies can range from just a few pairs to over 10,000 pairs. However, the species is described as nowhere ‘superabundant’, with large colonies of thousands of pairs being infrequent. This scattered nesting distribution and lack of large concentrations of birds contribute to the perception of the Arctic tern as a rare species.
Population Trends
Overall, the global population of the Arctic tern appears to be declining, though trends vary across different parts of its range. Declining trends have been observed in Europe and the eastern Canadian Arctic while some Arctic colonies in Alaska and Russia are stable or increasing.
The table below summarizes population trends in key areas of the Arctic tern’s breeding range:
Region | Population Trend |
---|---|
European Arctic | Declining 1-3% per year |
Svalbard | Stable |
Western Canadian Arctic | Declining 3.5% per year |
Eastern Canadian Arctic | Declining significantly since 1970s |
Alaska | Stable or increasing at some colonies |
Russia | Stable or increasing at most colonies |
These declining trends in parts of the Arctic tern’s breeding range also contribute to its rarity, as the species becomes less common and widespread.
Threats and Conservation Status
Several threats may be contributing to declining trends in Arctic tern populations in some regions. These include:
- Disturbance and habitat alteration at breeding colonies from human activities
- Increased predation pressure from polar bears, foxes, gulls, and other predators in some areas
- Changing climate conditions altering prey availability during the breeding season
- Bioaccumulation of contaminants such as mercury
The IUCN Red List categorizes the Arctic tern as Least Concern globally. However, it is listed as Endangered, Threatened, or a Species of Special Concern at regional levels in several parts of its range. These conservation designations often reflect declines in local populations, adding further support to the Arctic tern’s rarity in parts of its breeding distribution.
Breeding Habitat Specificity
The Arctic tern nests in a specialized habitat niche – low-lying coastal areas and inland marshes and lakes of the Arctic and subarctic. It requires areas free from predators with adequate food supplies nearby. As a ground-nesting species, habitat availability may limit its abundance and distribution more than for some other Arctic bird species.
The specific requirements for its nesting habitat prevent the Arctic tern from breeding uniformly and densely across the Arctic. Instead, it is restricted to suitable patches of habitat. This habitat specificity likely contributes to the limited size and scattered distribution of colonies, relative to some other seabirds.
Identification Challenges
Identifying and counting Arctic terns in the field presents some challenges that may lead to underestimates of true population size. Their migrations traverse huge distances, making it difficult to survey the entire population. At breeding colonies, their tendency to nest in scattered, low densities can make them hard to locate and monitor.
Away from nesting areas, Arctic terns can be challenging to distinguish from similar tern species, especially the very closely related Common Tern. This difficulty in identification can complicate population surveys.
Inaccessible Nesting Areas
The remoteness and inaccessibility of some Arctic tern nesting areas hinders efforts to fully survey breeding populations, likely resulting in underestimates. Colonies on isolated, hard-to-reach islands and far northern coastlines are logistically difficult and expensive for researchers to access. Some nesting areas likely remain unsurveyed, so a complete census of the global population is not feasible.
Vagrancy Records
Observations of vagrant Arctic terns far outside their normal range provide evidence that the species is not common and widespread. For example, Arctic terns observed during the breeding season as far south as Florida, California, and Japan likely represent wandering individuals far from their typical Arctic breeding areas. These rare vagrant records support the relative rarity of this species on the global scale.
Comparison to Other Tern Species
The total global population size of the Arctic tern is small compared to many other tern species. For example, the Least Tern has a global population estimated around 700,000 pairs while the Roseate Tern population is estimated at 360,000-530,000 pairs. The smaller overall population of the Arctic Tern, likely numbering less than 3 million pairs, contributes to its perception as a rarer species relative to these other more populous terns.
Population Size Compared to Other Terns
Species | Estimated Global Population (breeding pairs) |
---|---|
Least Tern | 700,000 |
Roseate Tern | 360,000-530,000 |
Arctic Tern | 1-3 million |
Conclusion
In summary, the Arctic tern’s specialized nesting habitat requirements, scattered breeding distribution, population declines in parts of its range, difficulty in monitoring, and small total population size relative to other tern species all contribute to it being considered a rare bird in many regions. However, its broad circumpolar distribution prevents it from being classified as globally threatened. Determining the rarity of the Arctic tern depends on whether the scale in question is local, regional, or global.