The incredible aerial athletes of the spring migration

Nature · Published 24 October 2026 Swipe more like this →

In short: From the screaming Swifts that sleep while flying to the mud-building House Martins, May marks a spectacular seasonal arrival. But as these long-distance travelers navigate the globe, they face a growing crisis of disappearing habitats and dwindling food supplies.

May serves as a pivotal moment in the avian calendar, particularly in the UK, when spring migrants arrive to breed. Among the most remarkable are Swifts, often called 'Devil Birds' or 'screechers' due to their piercing calls. These birds are elite long-distance athletes, undertaking annual journeys of approximately 22,000 km (14,000 miles). Their physiology is uniquely adapted for life in the air: they possess moveable bristles in front of their eyes to reduce glare, and they can eat, drink, and even sleep while in flight through a state known as torpor.

However, these aerial specialists are in significant decline. The UK’s Red List of Birds of Conservation Concern presently includes swifts. The population collapse is stark: in 1995, there were roughly ten Swifts for every ten seen; by 2022, that number had plummeted to about three. Researchers suggest the loss of nesting sites in the eaves and roof spaces of older buildings may be a primary driver of this decline.

Other migrants, like the House Martin, also rely on human-adjacent landscapes. Traveling from North Africa to Europe, House Martins build 'mud cup' nests using around 1,000 pellets of mud per nest. While once mistakenly believed to hibernate in pond mud, they are now known to nest in colonies near towns and villages. Interestingly, their social structure is quite fluid; up to 75% of nests contain chicks fathered by males other than the resident partner.

The challenges of migration extend globally. In the Delaware Bay, Red Knots arrive from the southernmost tip of South America, depending heavily on horseshoe crab eggs. Yet, the availability of these essential eggs is no longer as plentiful as it once was, highlighting the fragile links in migratory food chains.

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