‘Swallows high, staying dry’: migrating birds help predict weather

No sooner has spring turned into summer in the UK, then it seems as if autumn is here. We may have enjoyed a belated heatwave at the end of July, but a possible return of more unsettled weather reminds us that the breeding season is now over, and the return journey of migrant birds to Africa has already begun.

From mid-August onwards, birders on the coast hope for rain and wind, which grounds migrating songbirds that would otherwise fly overhead, unseen. Warblers, flycatchers and chats all migrate by night, stopping to rest and feed by day; so an early morning visit to a suitable habitat might produce surprises.

Those that feed on flying insects – notably swallows, martins and swifts – travel by day, feeding on the wing as they go. Again, local weather conditions are crucial: low pressure will bring the insects closer to the ground, followed by the birds, which swoop low to catch them.

But during spells of high pressure, on fine late summer evenings, look out for the same species flying high in the clear skies, hawking for invisible prey. We can even use them to predict the weather for the following day, as in the traditional rhyme : ‘Swallows high, staying dry; Swallows low, wet will blow’.

And then, as September gives way to October, they will leave us: off to enjoy a second spring and summer south of the Sahara, before returning next spring to delight us once again.