Arctic terns and Antarctic terns are seabirds that belong to the same genus Sterna. Despite their similar names, they live and breed in different polar regions and have some key differences.
Geographic Range
The most obvious difference between Arctic terns and Antarctic terns is their geographic breeding range:
- Arctic terns breed in the Arctic region, including Alaska, Canada, Greenland, Iceland, northern Europe, and Siberia.
- Antarctic terns breed in the Antarctic region, including the Antarctic Peninsula, South Georgia, the South Sandwich Islands, and other subantarctic islands.
During the non-breeding season, both species migrate long distances towards the opposite pole. However, there is little overlap between their ranges:
- Arctic terns migrate down to the Antarctic pack ice region.
- Antarctic terns migrate up to the waters along the coasts of Peru, Brazil, and southern Africa.
Migration
Both Arctic and Antarctic terns make extremely long annual migrations, but the Arctic tern’s migration is longer:
- Arctic terns fly from their Arctic breeding grounds all the way down to the Antarctic pack ice region and back each year, covering around 25,000 miles (40,000 km). This is the longest migration of any bird species.
- Antarctic terns fly about 15,000 miles (24,000 km) from their Antarctic breeding sites up to the coasts of South America, southern Africa, and Australia before returning south.
These epic pole-to-pole migrations allow the terns to experience summer conditions year-round, taking advantage of the seasonal abundance of food in both polar regions.
Breeding
The breeding habitats and nesting behaviors of Arctic and Antarctic terns also differ:
- Arctic terns nest in treeless tundra areas near water, often in rocky coastal areas or inland lakes and rivers.
- Antarctic terns nest on rocky, ice-free ground on subantarctic islands and the Antarctic Peninsula. They are less reliant on access to freshwater than Arctic terns.
Both species nest in colonies and lay 1-3 eggs in scrapes lined with vegetation or rocky debris. However, Antarctic terns have a longer breeding season lasting from November to early April, while Arctic terns breed from late May to August.
Appearance
Arctic and Antarctic terns are very similar in appearance, with gray and white plumage, black caps, red-orange bills, and forked tails. However, there are some subtle differences:
Trait | Arctic Tern | Antarctic Tern |
---|---|---|
Size | Length 28-33 cm | Length 33-36 cm |
Wingspan | 76-85 cm | 89-94 cm |
Bill color | Dark red | Orange-red |
Legs | Reddish | Blackish |
Crown | Jet black | Less deeply black |
In general, Antarctic terns average slightly larger with a paler bill color, darker legs, and a less deeply black crown. But these differences are subtle and variable enough that they can be very difficult to distinguish in the field without a direct side-by-side comparison.
Diet
The diets of both tern species consist mainly of fish, aquatic invertebrates, and some insects. However, there are some differences in their preferred prey:
- Arctic terns feed on fish like Arctic cod, capelin, sand lance, herring, and juvenile pollock. They also eat shrimp-like crustaceans and marine worms.
- Antarctic terns prey mostly on Antarctic silverfish and krill. They also consume some small squid and diving beetles.
This variation in diet reflects differences in food availability in the Arctic vs. Antarctic marine ecosystems where each species feeds.
Population Status
Both tern species have large global populations estimated in the hundreds of thousands to millions of breeding pairs. However, their conservation statuses differ slightly:
- Arctic terns are considered a species of Least Concern on the IUCN Red List due to their extremely large range and stable population trend.
- Antarctic terns are classified as Near Threatened, with decreasing populations likely due to climate change impacts on food availability.
Major threats to both species’ breeding sites include human disturbance, habitat loss, pollution, and predation by invasive species like rats. Climate change may also impact their migratory patterns and prey availability in the future.
Taxonomy
Arctic and Antarctic terns belong to the same genus Sterna in the bird family Laridae, which includes gulls, terns, noddies, and skimmers. However, they are considered separate species:
- The Arctic tern’s scientific name is Sterna paradisaea.
- The Antarctic tern’s scientific name is Sterna vittata.
This species separation is supported by molecular evidence as well as their distinct geographic breeding ranges, migratory patterns, and habitat preferences.
Hybridization
Despite being considered separate species, Arctic and Antarctic terns are known to occasionally hybridize where their breeding ranges come into contact:
- Hybrids have been documented in small numbers in the South Sandwich Islands and South Orkney Islands in the southern Atlantic.
- These hybrids show intermediate physical traits between the two species.
- However, hybridization seems to be relatively rare and limited to these few overlap zones.
The ability to interbreed to some degree supports the close evolutionary relationship between Arctic and Antarctic terns in the genus Sterna.
Conclusion
In summary, the main differences between Arctic and Antarctic terns include:
- Breeding ranges located at opposite poles
- Slightly longer migration distance for Arctic terns
- Subtle variation in size, plumage, and bill color
- Somewhat differing prey preferences
- Separate species status confirmed by molecular evidence
However, these terns also share many similarities as closely related seabirds in the same genus. Their epic pole-to-pole migrations are a remarkable feat of endurance, allowing them to take advantage of the great seasonal abundance of food in both polar oceans.
While Arctic and Antarctic terns may occasionally hybridize where their ranges interact, they remain ecologically well-separated for most of the year by their distinct breeding habitats and migratory behaviors. Conservation efforts are needed to protect the fragile polar ecosystems these amazing migratory seabirds rely on in our rapidly changing world.
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