Each autumn, several million birds funnel through the corner where the Pyrenees meet the Atlantic. It is one of the three best places in Western Europe to watch bird migration. It’s genuinely impressive, yet most who live here have never noticed and have no idea.
Every autumn, an estimated five billion birds leave Europe and head south for Africa. They are moving ahead of winter, following food and daylight, and most of them will make the return journey in spring to breed. A large share of these migrating birds are funneled into one narrow corner. That corner is the Basque Country.
The numbers are quite impressive. In 2024 the LPO counted more than 1.3 million migrating birds across its watch-points in this part of France. At the two main Basque mountain passes alone, observers tally well over half a million birds in a single autumn. Add the coastal wetlands, and the enormous number of small night-flying birds that nobody can fully count, and the true figure crossing the Basque Country each year runs well into the millions. Most people who live underneath all of this have no idea it is happening. How many birds did you spor?
Why birds migrate
Migration is one of the great feats of the animal world, and it is driven by something simple. In summer the north of Europe offers long days and a glut of insects and seeds, perfect for raising young. In winter that food vanishes. So billions of birds tackle the problem by leaving, flying thousands of kilometres to the south, then coming back when the north turns fertile again. A small warbler weighing less than a coin can cross the Sahara twice in a year.
How they do it is still partly a mystery. Many large birds travel by day. Most small ones travel at night, when the air is calmer and predators are asleep, navigating by the stars, by the position of the setting sun, and by sensing the Earth’s magnetic field. Ringing studies show that individual birds often return to the exact same hedgerow year after year, having found their way there across a desert and back.
Most migration happens on a broad front, with birds spread out across the whole sky. But geography can squeeze that front into a narrow line. Coastlines, mountain ranges and narrow sea crossings all concentrate birds into corridors, and where the corridor pinches tight you get a bottleneck: a place where a huge share of a whole continent’s birds passes through a single valley or strait.
Map of East Atlantic Flyway that hangs in Urdaibai Bird Center
The world’s great funnels
There are eight major flyways around the world, the broad highways that migrating birds follow between continents. The busiest bottlenecks on them are famous among birdwatchers. At the Strait of Gibraltar, where just fourteen kilometres of sea separate Spain from Morocco, observers count around 300,000 birds of prey and 150,000 storks every autumn. The Bosphorus in Turkey, the Strait of Messina in Italy and Falsterbo in Sweden all do something similar, gathering birds that are prefer not to fly out over open water.
That reluctance is the key to everything. Large soaring birds, the eagles, buzzards, kites and storks, do not flap their way to Africa. They ride thermals, columns of warm air that rise off sun-heated ground, spiralling upward for free and then gliding forward for kilometres before catching the next one. Thermals form over land, not over open sea. So a soaring bird will not cross a wide stretch of water if it can help it.
This is where the Basque Country earns its place on the map. It is the westernmost of Europe’s great migration funnels. Birds pouring down the Atlantic flank of the continent reach the Bay of Biscay and refuse to cross it. They follow the coast until it meets the wall of the Pyrenees, and the whole western edge of Europe narrows to a point right here. It is a place they are forced to pass. Many of them, having crossed here, will carry on down through Spain to Gibraltar and into Africa. In that sense the Basque passes are the top of a funnel that ends at the strait.
Three mountain passes, two estuaries
Most of the soaring birds cross at three high passes: Col d’Organbidexka just west of Larrau, Col de Lizarrieta above Sare, and Col de Lindux on the Navarrese border. A little further out, the coastal wetlands catch a completely different crowd. Txingudi, where the Bidasoa river meets the sea between Hendaye, Irun and Hondarribia, and Urdaibai near Gernika, pull in the waders, ducks, herons and spoonbills that follow the shoreline south. Same flyway, but different travellers.
The star site is Organbidexka, a pass at around 1,300 metres above the forest of Irati, the largest beech forest in Europe. Along with Falsterbo and Gibraltar it is rated one of the three best places in all of Western Europe to watch migration. People have counted birds here every single day, from 15 July to 15 November, since 1979. The 2025 season was the 47th in a row.
Col d’Organbidexka above the Iraty Forest, taken in 1964 by Daniel Villafruella
A season in the sky
The passage is like a slow parade, and the cast changes week by week. From a nice viewpoint you can see a flock slowly arrive from the north and you can identify and count them as they come closer. The show opens in July with black kites, which despite the name are really grey-brown, with a shallow forked tail. On a single early-August day, observers here have counted more than 5,000 of them. Around the middle of August comes the famous “switch”, when the kites thin out and the honey buzzards take over. The honey buzzard is a strange bird with an almost pigeon-like head that specialises in digging out the nests of wasps and bees and eating the grubs.
Then the parade broadens: short-toed eagles that live almost entirely on snakes, booted eagles no bigger than a common buzzard, ospreys, sparrowhawks, and both black and white storks. October brings red kites and the first cranes. November brings the cranes in force, along with rivers of small birds. In the 2025 season the team logged more than 21,000 cranes crossing the pass, over 4,000 great cormorants, more than 1,100 red kites in the closing weeks, and, on one astonishing day, a ribbon of bramblings that streamed overhead for five minutes without a break.
The nearby pass at Lindux, counted jointly with Navarrese ornithologists from the group Ornitolan, is even busier by raw numbers, with recent seasons topping 367,000 birds and a single day of more than 21,000 cranes moving through in long calling lines.
How many kinds of bird are we talking about? In one autumn, counters at a single pass record around 80 species in active migration. Over the years, more than 200 species have been logged crossing Organbidexka. Add the coastal wetlands and the total for the region runs to several hundred, everything from great cormorant to chaffinch to buzzard. And over some of those ridges patrols the bearded vulture, a bird with wings close to three metres across that lives almost entirely on bone and cracks the biggest ones by carrying them high and dropping them onto rock.
The pigeon puzzle
One bird tells a more complicated story. The wood pigeon, the palombe, is woven into Basque life. In the Pyrénées-Atlantiques there are around 17,000 people who hunt it, and the tradition of watching for the great autumn flights is centuries old. Hunters have counted the passage from these same passes since 1988, in their own parallel survey.
Here is the surprise. The palombe is not disappearing. Its breeding population in France has grown by more than 150 percent over the last three decades, and a growing share of birds now stay north through the winter instead of migrating at all. Yet the number crossing the high Basque passes has been falling for years, with recent seasons the lowest ever recorded at Organbidexka. The birds are thriving. They are simply changing their route, drifting west and skipping the mountains. The spectacle at the cols is fading even as the species does well.
Wood pigeons migrating as seen over Guethary (France) in 2023
What it means, and why it needs space
A migration on this scale is not just a show. It is a moving thread that ties the ecosystems of half a continent together, carrying predators, seeds and nutrients from the forests of northern Europe to the wetlands of West Africa. And it only works if the birds can rest and refuel along the way. A bird that has flown for days needs somewhere safe to land, feed and recover before the next leg, which is exactly what the coastal marshes and quiet valleys of the Basque Country provide. When those places are drained, built over or disturbed, the birds do not simply move next door, they are in trouble.
That is the real value of 47 years of daily counting from the same pass. Half a century of numbers is an early-warning system, and it is already flashing. The steady fall in red kites crossing here matches declines found far to the north on their breeding grounds. Read from one mountain in the Basque Country, the sky is telling us how the birds of an entire continent are doing.
It is happening over your head
The best part is that you do not even need to climb to a mountain pass to see it. The passes are where the birds are counted, but the migration spills out across the whole territory. From the coast, from a beach or a garden or a town square, you can watch cranes cross in long calling lines, spoonbills and cormorants pass overhead, barn swallows pour south in their thousands, and flocks of wood pigeons stream along the shore. It happens every autumn, on a predictable schedule, over Bayonne and Biarritz and San Sebastián as much as over the Pyrenees. The birds have been doing it for far longer than there have been people here to watch them. Just make sure to look up now and then. And have binoculars ready!
In the next articles we look at why this small stretch of coast and mountain matters so much on the map of European migration, and at where and how you can watch it for yourself, and help.
