It is the most miraculous bird, the ultimate winged messenger, exploring our globe, spending its life on the breeze. Sickle-shaped wings silhouetted against the sky, the swift is the fastest of all birds in level flight and remains entirely airborne for 10 months, or more, feeding, sleeping and mating on the wing. These long-lived creatures can clock up four million miles, commuting between English summers and African winters.
Something has changed though. June is erupting as gloriously as it ever did: roadsides are waving with oxeye daisies and blackbirds flute during the endless evenings. But summer is a shadow of its former self. The swifts aren’t here.
Well, they are. Only not as we knew them. I heard a scream just now, felt that start of wonder, and glanced up. One swift. No – three, darting through the blue. Three birds. It’s like returning to the place where you grew up and finding your old home bulldozed. Reality does not compute with the picture you remember. I knew the swift for its screaming parties, marvellous groups of 20 or 40 or 60 or uncountable numbers of birds racing together through the sky, flicking their wings, calling in apparent glee.
But this bird is in freefall. A graph produced by the British Trust for Ornithology is terrifying: the British population declined by 51% between 1995 and 2015. And the rate of decline is increasing: down 24% in the five years to 2015.
The decline of globalised animals is always global, and complicated. So the disappearance of other equally charismatic long-distance migrants such as nightingales, cuckoos and swallows is bound up in habitat loss or changes in Africa, as well as Britain, and climatic changes en route.
Living in roofs, swifts have also suffered from the conversion of derelict buildings, and our desire for more energy-efficient, impermeable homes.
But the biggest cause of changes in animal populations is always food supply. And guess what? Swifts feed on flying insects.
We are belatedly waking up to the global calamity that is the loss of insect life. The German study showing a 76% decline in flying insects since 1989 is no anomaly. In Britain, for instance, three-quarters of butterfly species have declined over 40 years, while moth abundance has fallen by more than 40% in the southern half of the country.
Do not accept the vanishing of the swifts. This week is the first swift awareness week, anywhere in the world. Enthusiasts are taking action: counting swifts, putting up special nestboxes, telling their neighbours to make space for them too.
We should be marching on Westminster about this threat to life. And yet, if we imagine hundreds of thousands of us brandishing banners depicting moths or birds, shouting, “Save our swifts!”, it is preposterous, or comical. It shouldn’t be.
• Patrick Barkham writes for the Guardian on natural history