Swifts are our most aerial bird, spending almost all their entire lifetimes airborne, apart from a brief period in the nest. Growing up in London, for me swifts were the first sign of summer – usually appearing in early May. But the climate crisis means they are now arriving two or even three weeks earlier – like the birds that flew over our garden on 21 April 2020, during that first Covid lockdown. This spring, there has been an unprecedented influx of their larger and scarcer relative: the alpine swift. These are like a common swift on steroids – twice the weight, at 100 grams, and with a 57cm (almost 2ft) wingspan. Each spring, a handful of alpine swifts overshoot their intended destination of southern Europe and turn up here. In mid-March 1990, no fewer than 14 arrived after intense high-pressure over the continent. But this spring dozens have been seen, some as far north as Scotland, where the species is very rare. They arrived on south-westerly winds – but that may not have been the only reason they came. The effects of the climate crisis on birds that breed around the Mediterranean may be encouraging these species to seek more equable places to nest. As with the bee-eaters, which raised three chicks in Norfolk last year, alpine swifts could soon stay here to breed.