Sensational Swifts
Which bird immediately springs to mind when you think of the ‘ultimate flying machine’? How could it be any other than the Swift?
Why Ian Parsons considers the Swift to be the ‘Ultimate Flying Machine’!
There are many people that refer to the Peregrine as the ultimate flying machine, but I am not one of them. For me, that moniker can only belong to the Swift. After all, Peregrines spend much of their time not actually flying, while the Swift spends all of its time flying; eating, sleeping, drinking and even mating on the wing. If it wasn’t for egg laying and incubation, the Swift would probably never, ever, touch down. I suspect that for many of us, the Swift is high up on our favourites list; a screaming party dashing at breakneck speed around the rooftops is a summer sight and sound that is hard to beat. Yet for all its popularity, the Swift is a bird that only visits us for a short time every year, arriving at the end of April and departing again during August – they hardly spend a hundred days with us. Their stay is indeed brief, but then again, as their name suggests, these are birds that don’t hang around. Of the 100 or so species of swift worldwide (taxonomists can never agree!), the Swift is the only member of the family that breeds in Britain. This is a statement that often confuses nonbirders, who presume that the similarlooking martins and swallows must be closely related to the swifts. They aren’t of course, but it is easy to see why people may think so, as they do share a basic body shape and fly in a superficially similar way. However, martins and swallows, collectively known as the hirundines, are passerines (or perching birds), and Swifts are most definitely not perching birds! The scientific name for the swift family is Apodidae, taken from the Latin meaning no feet. Now, swifts do have feet of course, but they are proportionally very small and very weak, pretty useless in fact, and they certainly couldn’t perch if they tried! Swifts are actually closely related to the hummingbirds, a group of birds that are also flight specialists. The Swift is the most aerial of our breeding birds – put simply, its habitat is the sky. No other British bird spends as much time on the wing as the Swift and they certainly rack up the miles. It is estimated that a Swift will comfortably fly 125,000 miles a year! And what flyers they are; spend time watching Swifts in flight and you will be awed. Agility, grace and speed are combined into perfection as the birds completely outfly anything else in the air. Try following them through binoculars and you will soon appreciate why they are called Swift, their speed and their ability to make sudden changes of direction will soon cause you to lose them or, as once happened on one of my tours, cause you to swing violently round and hit the birdwatcher next to you in the face with your bins.
Feeding in flight
Swifts are invertebrate feeders, catching a wide range of insects and spiders in flight; they use their mastery of the sky to hunt above all habitats, from cities through to moorland and even over open ocean. They are excellent readers of the weather and use this to their advantage when feeding. Approaching weather fronts can force flying invertebrates into swarms, which are then driven upwards by air currents to heights of a kilometre or more. This concentration of food is irresistible to Swifts, who readily exploit it, often flying some distance to do so. They will also fly considerable distances to avoid bad weather; a low-pressure system barrelling in off the Atlantic can make life for many birds very difficult – the Swift though flies around it, sometimes flying 500 miles in one day to do so! This is a great way to avoid bad weather, but Swift chicks, land-locked in their nest cavities can’t do this, so how do they cope when their parents are away? If you look through a bird book you will often find the length of time a bird takes from hatching to fledging. For a Blackbird for example, it is given as 14-16 days and for a Swallow it is 20-22 days. There is always a bit of variation in the exact number of days taken, but it is normally just one or two. However, for a Swift it is 37-56 days and that is a variation of 19 days! For most birds, chicks will soon die if the parents are unable to feed them
regularly. If a Blackbird stopped feeding its brood because of bad weather, then that brood would soon perish, but when a Swift flies off to avoid bad weather the chicks don’t die. Instead, they do something that you don’t normally associate with a Swift – they slow down.
Chicks’ survival strategy
Swift chicks are able to slow down their metabolism and enter an almost torpid state. Only the basic body functions continue and the young chicks are able to fuel these processes using stored fat, but the high-energy demanding processes such as growth and feather development are slowed right down. Once the weather improves and the adults return, the chick’s metabolism kicks back into gear and they can continue to develop as normal, albeit a few days behind where they should be. This is an unusual adaptation, but it is one that is very useful in a British summer! Once the chicks fledge they might not land again for three years. Three years of continuous flight – remarkable when you think of it, but for the Swift it is perfectly normal and means that when a female lays her first brood she has probably been flying non-stop for more than 300,000 miles (by contrast the moon is ‘just’ 239,000 miles away!). Everything they do is aerial. They drink by skimming the surface of bodies of water as they fly over them or by catching raindrops mid-air, they mate while flying and even sleep on the wing. This isn’t as potentially dangerous as it sounds, for the Swift doesn’t sleep like we do. It sleeps by shutting down one half of its brain at a time, allowing the bird to function normally while still getting the rest that it needs. A perfect adaptation for a bird that spends so much of its life on the wing. The Swift might not be with us for that long every year, but it is a definite favourite and one that we should all enjoy. It is an extreme bird, perfectly honed for an aerial life – the ultimate flying machine.