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I VERY much enjoy autumn’s display of golden leaves and fungi, but as a bird lover in the UK, the real thrill at this time of year is the influx of migratory birds that arrive from Scandinavia, Iceland, Eastern Europe, Siberia and Canada. I am pleased to have already seen redwings this season.

The UK is lucky when it comes to bird migration – in the winter, we get a wide variety of birds heading here to escape harsher conditions further north. And then in spring and summer, we are visited by birds from Africa such as swallows, chiffchaffs and cuckoos that make the most of our long, light days for having their young.

While the long flights taken are undoubtedly impressive, there are some species that fly considerably further, spending much of their lives at the extreme ends of Earth, flying vast distances to enjoy an almost unlimited summer.

I was lucky to get a glimpse of this years ago, while whale watching off the coast of Japan. We happened upon thousands of short-tailed shearwaters: black seabirds that migrate in huge numbers. After breeding between September and April in Tasmania and southern Australia, the shearwaters head to the far eastern edge of Russia and then Alaska to feed, before travelling back south along North America’s western coast and then returning home to the same burrow.

But shearwaters aren’t the record holders when it comes to sun-seeking birds. The Arctic tern has the world’s longest migration: a round-trip of 35,000 kilometres annually. Arctic terns break up their long journeys though, so if you are looking for the world’s longest non-stop flyer, that record is held by the bar-tailed godwit. One of its subspecies breeds in western Alaska before flying non-stop down the middle of the Pacific Ocean to New Zealand or south-east Australia, a flight of about 11,000 kilometres in eight days or so. Last month, an individual arrived in Tasmania after – 13,560 kilometres covered in 11 days and 1 hour.

The science of migration has many interesting avenues – how do birds prepare, navigate and know where to go? One central question is: why do it? What is the benefit – and if there is one, how did evolution stumble across it?

There is still much we don’t know, but we do know more than we did a few hundred years ago, when we thought that when swallows disappear, they went to the moon or were . As for why they do migrate, some journeys are easier to explain. It makes sense to head somewhere warmer for winter, but it can be harder to explain why, for example, some African species then return to Europe for summer when food is still plentiful in their wintering grounds. It could be because there is less competition here, or because our longer, cooler days are useful, or simply because there is food ready to be exploited. Some trips are even harder to explain. For example, the ancient murrelet flies almost 8000 kilometres from Canada to Japan and China, despite very similar conditions.

One thing I have always wondered is how a bird could evolve such a long migratory route. One idea is that plate tectonics played a role, gradually pushing suitable seasonal habitats further away from each other by a few millimetres a year, until they were many kilometres apart.

However it initially arose, migration became genetically encoded in various species. Experiments with young captive European blackcaps have revealed that the birds inherit a preference for the direction they would like to travel in. And of course young cuckoos, which grow as parasites in the nests of different species, know to migrate like other cuckoos, without having met any.

But it turns out this isn’t the case for all migratory birds. A published earlier this year revealed that young Caspian terns are closely accompanied by their fathers on their first migration from northern Europe to Africa. Any young birds that lost contact with their dads during the early stages of migration died. The following year, when the surviving birds migrated solo for the first time, they closely followed the routes taken with their fathers.

We don’t yet know the full details of how the world’s long-distance migrators evolved or learn their routes. But it is clear the benefits of such a perilous journey may not be stable in our changing climate. When Arctic terns arrive in the northern hemisphere, they are hungry for sand eels. In 2004, the UK saw a sudden drop in sand eels, thought to be due to climate change. , the Shetland Islands usually hosts more than 20,000 pairs of Arctic terns, but didn’t see a single chick survive to adulthood that summer. I have so much admiration for the world’s furthest fliers – I just hope they can cling on and that we can come to fully understand them.

Penny Sarchet is Â鶹´«Ã½â€™s news and digital director. She is a former plant scientist and a lifelong birdwatcher. You can sign up to her free monthly newsletter at
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