9 May: Swifts

The first Saturday in May is International Migratory Bird Day, so here are ten facts about a migratory bird, the swift.

1. Swifts have one of the longest migration distances of any bird. They will travel 14,000 miles (22,000km) every year, passing through the airspace of around 25 countries in order to get where they want to be. They can reach speeds of just under 70 miles an hour.

2. They do everything on the wing and only land to breed (having mated in flight first). They drink either by catching raindrops or skimming pools. Making a splash as they do so allows them to bathe. They eat flying insects. Swifts eat as many as 100,000 flying insects a day.

3. To sleep, they ascend to high altitudes, as high as 10,000ft, where there are no predators to bother them. Once there, they sleep by shutting down half their brains, so one half can monitor the wind drift so they don’t get carried too far away from where they started.

4. Hence you’ll never see a swift perched anywhere. They have only tiny legs and claws, only used for landing on their nests. Once at rest there, they flop about in an ungainly fashion on their chests.

5. They make their nests out of anything they can gather on the wing, feathers and saliva. They originally evolved to nest in high places like cliffs, but since humans started building houses, their preferred homes are the eaves of houses and spires. They’ll return to the same site year after year. Incidentally, the nests of a species of swift native to Asia are what is used to make birds nest soup.

6. On summer evenings, groups of up to 20 birds will gather for a “screaming party” during which the nesting swifts and the ones that aren’t breeding this year call out to each other. Even larger groups may gather at higher altitudes.

7. Historically, swifts have been known as "The Devil's Bird". Which might be because they disappeared for months on end, before naturalists figured out they were simply relocating somewhere warmer for the winter; that and the fact that even when they are around, it’s virtually impossible to catch one.

8. That said, they were eaten in medieval Italy. People encouraged swifts to nest on buildings and would steal the young birds from the nests. There were strict rules stating that one young bird must always be left alive in the nest.

9. You can tell them from Swallows and martins because swifts are larger, and have a pale patch on their chins.

10. The heraldic bird known as the "martlet", pictured without feet, may have been based on the swift, although house martins are also the possible models. Martlets often appeared in the arms of younger sons, who didn’t inherit the land and were therefore destined for rootless wandering.

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