First things first! I’m at Science Rendezvous Kingston today with some friends and fellow science writers. If you’re in the area, come on down! It’s free and suitable for all ages.
In 2014, Tech Support and I were lucky enough to visit Iceland during June, when migratory birds were nesting. We saw puffins and petrels and gulls and guillemots packed onto jagged cliff edges. But what I remember most is walking through the field back to the tour bus and getting dive-bombed by arctic terns who’d built their nests in the long grass flanking the path.
Today is World Migratory Bird Day, making it the perfect day to talk about terns – the champion migrators of the biological world. Adult terns weigh about 100 g, and every year, they make round-trip journeys of up to 50,000 km. 50,000 km, at speeds of up to 670 km per day.
The “legs” of a tern’s journey are typically different lengths, but for the ease of math, let’s assume they are the same. That’s 25,000 km one-way. The record one-way migration for an adult male humpback whale is 18,840 km.
Terns can live more than 30 years, meaning one tern might travel more than 2.4 million kilometers during its lifetime. That’s the equivalent of about three trips to the Moon and back. I’m exhausted just thinking about it!
What could possibly motivate such teensy birds to make such epic journeys? Well, terns nest in the Arctic, during summer in the Northern Hemisphere: they’re arriving at their breeding grounds right around now.
Terns molt – shedding old feathers and growing new ones – in Antarctica, during summer in the Southern Hemisphere. In other words, terns never experience winter: they are always in the right place, at the right time, to take advantage of long summer days and mild temperatures.
Migration timing also seems to be linked to periods of peak ocean productivity. Scientists tracking terns with tiny GPS loggers have shown that terns arrive in each staging location right when the most fish and krill are available to eat – important, because those rich food sources give them the energy they need to keep going. When they reach Antarctica, they also tend to hang out on icebergs or the edge of the pack ice. This gives them solid surfaces to rest on, but really easy access to open water for fishing in.
For terns, the benefits of their extreme migrations seem clear. But migration is not without its risks – for terns and many other species. All that travel takes a ton of energy. Birds can get lost or blown off course in bad weather. They have to pass through areas of unsuitable habitat – places without food, or places inhabited with unfamiliar predators. Birds that orient using natural light cues often get confused by the lights of human cities.
That’s why many migratory bird species are protected under the Migratory Birds Convention Act. You can explore the list of species protected in Canada at this link. Arctic terns are included!
For some ways you can help protect birds this World Migratory Bird Day, check out these lists:
Five Ways You Can Make a Difference for Migratory Birds
Six Ways to Help Migratory Birds
10 Ways to Help Migratory Birds
Arctic terns are one of several migratory birds that appear in Polar: Wildlife at the Ends of the Earth. The book is out now – grab your copy at your favourite indie bookseller, or one of the online retailers below:
I’m doing a Polar presentation at the Brighton Public Library on May 30, and I’m still booking Polar-themed school visits this spring! Contact me to inquire about dates and rates.