In 2015, researchers from Newcastle University fitted geo-locators to 29 terns at a breeding colony on the Farne Islands off Northumberland. The tiny devices logged the positions of the birds from day to day. Sixteen of the terns were recaptured back at the colony this summer and their locators retrieved. One of the units revealed that, on leaving the breeding colony, the tern had flown south along the west coasts of Europe and Africa.
It rounded the Cape of Good Hope into the Indian Ocean and worked its way down to the east coast of Antarctica, arriving there twelve weeks after it had set out. Last April, the bird headed back to the southern tip of Africa and up the Atlantic seaboard to the North Sea coast of England. By the time it reached the Farne Islands, this gold-medal- winner had flown 96,000km.
The previous long-distance record, made by a tern breeding in the Netherlands, had been 91,000km. Arctic terns are long-lived creatures; a ringed one reached the ripe old age of 34. Assuming it completed similar journeys each year, the bird had travelled more than 3,000,000km during its lifetime. No living thing, apart from airline-crew members and ‘frequent flyers’, clocks up more kilometres.
Needless to say, the extraordinary journeys made by terns are not just products of brute force; as with human athletics, intelligence and calculation are required. Birds choose their routes so that the prevailing winds help carry them along. In a 1997 study of flying seabirds, researchers estimated that winds can account for up to 60% of the variation in ground speeds.
Despite the enormous distances they cover, terns manage to arrive back at their breeding sites at close to the same date every year. According to a paper just published in Ringing and Migration, Arctic terns showed up at colonies in Troms, north Norway, within a 13-day period each May for the last 35 years. The true ‘arrival window’ is even narrower.
Local winds, blowing from the north as the birds approach Troms, can delay their arrival for a few days, while southerlies may carry them in early. Considering the huge journeys they make, flying at 30kph to 40kph per hour, the terns’ navigational skills and timing are extraordinary.
Comparisons with Rio, of course, aren’t really valid. Human athletes keep breaking new ground through blood, sweat, tears and technology; it’s unlikely that anybody in the 200,000 year history of our species has equalled the athletic feats of today. Animals, however, have no interest in records. They just do what they have always done; terns have been flying huge distances for millennia. We simply had no way of measuring the extent of their journeys until now.
That Arctic terns visited Antarctica was known from ringing. On a visit to Hornoya Island in the Barent’s Sea this summer, I found the terns there as active and noisy under the bright midnight sun as they were at midday. The sun hardly ever sets on these Nordic birds. Spending the winter in the southern seas, they see more daylight than any creature on Earth.
This slender grey and white Arctic ‘sea swallow’ has a black skullcap, longish tail- streamers, red legs and a bright red bill. Distinguishing it from the common tern can be difficult. Even experienced birdwatchers lump the two species together as ‘comic’ terns. The Arctic tern nests in Ireland, at the southern limit of the species’ European breeding range.
- R Barrett. Upwind or Downwind: the spring Arrival of Arctic Terns at Troms, North Norway. Ringing & Migration. June 2016.