Arctic Terns: Greatest Endurance Athletes on Earth

The arctic tern or Sterna paradisaea is one of the most impressive animals on Earth and since I began running long distance, I have always looked upon it as my power animal, whatever that means. The arctic tern belongs to Order charadriiformes, and family Laridae, a seabird family consisting of gulls, terns, and skimmers.¹

Arctic terns are a medium-sized bird, with a wingspan of about 76–85 cm and a weight of 86–127 grams.¹ Their life expectancy is an unusually long 30 years. This means that over a lifetime an average Tern could fly over 2,127,000 kilometers or roughly 1,321,656 miles.² My life goal of 150,000 running miles pales in comparison.

Arctic terns are monogamous birds that mate for life. In addition to their bond with a mate, they also live and migrate in large colonies.³ They feed mainly on fish and krill, which they grab by skimming the surface of the water.² Despite a lifetime of flying over large oceans, terns are poor swimmers and tend to avoid water when not fishing.³

Arctic terns have the longest migration of any animal on Earth covering a staggering 81,600 kilometers or 50,703 miles in a calendar year.³ That means that in just one year, Arctic terns fly a distance that has taken me 15 years to reach. As a caveat, your average tern travels a modest 70,900 kilometers per year (not every tern grinds out that extra 11,000 kilometers). In addition to covering an inconceivably long distance, they also see more sunlight than any animal on earth spending June through August near the north pole and December through April in the south pole.³

After my failed Washington Pacific Crest Trail speed attempt, I thought a lot about the animal that I most admire. What qualities do arctic terns possess that make them much better equipped to cover long distances?

1. Without belaboring the obvious, there is no way that terns could survive the frigid, dark, cold Arctic and Antarctic winters without migrating to another location. They must find food and nesting locations that allow them to avoid predation. Their need to travel long distances is not arbitrary but is hardwired into their genetics. This means that no matter how ambitious and motivated I am, traveling long distances will always be merely a fool’s pleasure, not a means of survival.
2. Unihemispheric-monocular sleep. Many species of birds possess the ability to shut down one side of their brain to rest and recover, while the other side continues to carry out the task of flight.⁴⁵ While this method of sleep-flying has not been confirmed in arctic terns specifically, it is a likely hypothesis. On the PCT, when my body became too tired to press onward I collapsed into the bushes. However, when the arctic tern becomes tired, it simply shutdowns half of their brain to rest while continuing on their journey. Through specific training I could become better equipped to handle sleep deprivation, but acquiring the ability to sleep-run is not in the cards.
3. During my college running years, I cut a considerable amount of weight, dropping from 170 pounds to 144 pounds. This meant that I was ravenously hungry during my waking hours, but could also run 2 minutes faster in a 10,000-meter race. Arctic terns are a scant 100 grams and carry no extraneous body fat. They are also able to fluctuate their weight based on whether they are breeding or migrating.⁶
4. Arctic terns have a high metabolic rate and must eat not only to fuel their ambitious journeys, but also to maintain a warm internal body temperature in the cold climates they inhabit. Terns select food that is high energy and easily digested.⁶ While I fumble around with gels and waste time at aid stations, Terns simply skim the top of the water and pick out fish or krill. My ability to hunt and forage on the run is minimal, so once again; the arctic tern’s resourcefulness is superior.
5. Arctic terns are some of the fiercest defenders of their nests and young in the animal kingdom.² Arctic terns will even dive bomb a Polar Bear if it comes too close to their territory. Now, of course I would not attack a competitor in a race, but if I had even half of the aggressive mentality of the arctic tern, perhaps I would not give up my position nearing the end of a race.
6. All the previous qualities are crucial to arctic terns success in ultra distances, but without efficiency of movement, none of them would matter. Arctic terns have been known to fly up to 1000 miles in a single day, and that could not happen without proper aerodynamics. They can adjust their tail feathers depending on the wind, their bones are hollow, and their bodies are streamlined for long distance flight.³ This is another quality that I can work towards, but never fully achieve to the same degree as the arctic tern.

Terns possess numerous qualities that make them the top ultra endurance athlete in the animal kingdom, but perhaps the best way to showcase that is in an Arctic tern trip report…

I started out 2020 on a rocky island in northwestern Antarctica and with the exception of hunting for fish and krill; I took about 150 days off to rest up before my south to north Earth traverse. Last year I began my northbound speed attempt on April 16^th trying to beat the winter season and leverage the good weather. I kept a good pace and passed the equator a little faster than I anticipated, on May 3^rd (17 days). After reaching the equator it only took me another 23 days to reach my destination on Sand Island in northeastern Greenland.²

Sand Island is my favorite place to rest and assist in raising my chicks. The island has a lot of charm; it is quite small, only 1 kilometer long and 0.3 kilometers wide. It is mostly mixed with sand and gravel but near the center of the island there are some nice willows.⁷ After 40 days of intense flight covering about 25,000 miles at a 625-mile per day pace, I was ready for some rest with my breeding colony.²

I spent May 26^th through August 1^st on Sand Island, successfully raising two little arctic terns among the boisterous colony. On August 1^st my friends and I fell silent; this is what we arctic terns call, “dread.” All at once we took to the air to return to our summer home in Antarctica. After my successful northbound FKT, I decided to take it easy on my southbound Earth traverse. I stayed with the colony and flew along the coast of Greenland into the central north Atlantic.²

On the way north it was all about speed, but on my southbound route I took a 24-day rest at an aid station in the north Atlantic. So between August 22nd and September 15^th we enjoyed some of the most productive ocean around. From year-to-year, we locate a spot with high eddy variability between cold and warm water masses and what results is a feast of fish and krill.²

I reluctantly left the aid station and continued with the colony over to the west coast of Africa. Many of my friends took the route along the west coast of Africa, but this year I decided to cross the Atlantic and skirt the coast of South America. I like to change it up from year to year to keep things interesting. Finally after 93 days on the wing, I reached my winter home in Antarctica on November 24^th.²

As I reflect on my 50,000-mile journey I realize how fortunate I am to have the ability to complete such an amazing journey. My long migrations allow me to see more sun than any other animal on Earth. I am well on my way on my quest to reach 1.5 million miles and perhaps next year I will push to lower my traverse time to 36 days.

References

1. Dunn J, Alderfer J. Field Guide to the Birds of North America. Fifth Edition. National Geographic Society; 2008.
2. Egevang C. Migration and breeding biology of Arctic terns in Greenland. :107.
3. Ramroop T, West K. To the Ends of the Earth. National Geographic. https://www.nationalgeographic.org/article/ends-earth/. Published January 16, 2011.
4. Mascetti, Gian Gastone GG. Unihemispheric sleep and asymmetrical sleep: behavioral, neurophysiological, and functional perspectives. Nat Sci Sleep. 2016;Volume 8:221-238. doi:10.2147/NSS.S71970
5. Rattenborg NC. Sleeping on the wing. Interface Focus. 2017;7(1):20160082. doi:10.1098/rsfs.2016.0082
6. Uttley J, Monaghan P. Measuring the Daily Energy Expenditure of Free-Living Arctic terns (Sterna paradisaea). The Auk. 1994;111(2):453-459. doi:10.2307/4088609
7. Egevang C, Stenhouse I. Field Report Sand Island. Published online 2007:10.