The famous wildebeest migration of the Serengeti and the great salmon run of North America are just two examples of epic migrations undertaken by animals – and they both pale in comparison to a small seabird that weighs less than half a pound: the Arctic tern.
The name ‘Arctic tern’ is somewhat misleading because it only spends half of its time in the Arctic Circle. Sure, it mates and breeds there but then it leaves and casually travels all the way to the Antarctic on the opposite side of the planet to ‘overwinter’ – although by the time it gets to the South Pole, it will be summer there as well. Since it experiences two summers a year, and because the sun never dips below the horizon during these polar summers, the Arctic tern may not necessarily experience a wealth of gloriously high temperatures but it does see more daylight than any other animal on the planet.
And that’s not the tern’s only claim to fame. Pole to pole, the journey that it undertakes is at least 12,000 miles, and that’s assuming that the bird travels in a straight line – which it never does. Then, after spending the southern summer in the Antarctic, the terns head back to the North Pole again, once again making the immense journey. The round trip covers around 44,000 miles, by far the longest and greatest animal migration on Earth. Since some terns can live to be thirty years of age, they can fly a staggering 1.5 million miles during their lives – that’s the equivalent of travelling to the moon and back three times.
Being a seabird, the Arctic tern can occasionally stop and rest on calm waters and even catch fish, so it cannot be counted as a non-stop flight. The longest migration without a single pit stop, therefore, is made by an unassuming wading bird called the bar-tailed godwit. It travels from its breeding grounds in Alaska and Siberia to New Zealand – around 6,800 miles – without taking a break to eat or sleep. Even though it crams itself with food before the mammoth journey begins, it probably wouldn’t be able to survive the ten day non-stop flight without one amazing adaptation: it starts to consume its own internal organs.
When the day of its departure comes, the bar-tailed godwit may have broken down up to a quarter of its internal organs, including its liver, kidneys and intestines. This not only creates even more space for fat – its body may be 55% fat by the time its migration begins – but it also saves the energy that would otherwise be used in maintaining such organs, which, though normally vitally important, are almost useless during its trip. You could say it’s a rather more questionable version of an in-flight meal.