Monday, 22 August 2011

They're back! The swifts return...

Eurasian or Common Swifts, Apus apus, are not the most exciting of birds to look at (nor, here in Africa are they one of the easiest to identify, given their similarity to both African Black swifts and Nyanza Swifts), but they arrived back over Arusha at the weekend (and I'm told100s arrived back in Serengeti at the same time) and are real signs of the changing seasons. They're also absolutely fascinating things.
Common Swift (from Wikipedia)

Unfortunately, I've not got a photo of my own to share, so I've had to borrow this from Wikipedia. Firstly, you want to identify the thing. Swifts and swallows are often confused, but they're actually fairly simply to separate. Swifts are (usually) larger, have have long, stiff wings which they hold out sideways and only flap from the base of the 'arm', whilst swallows are (usually) smaller and have active flapping flight bending the wing at the 'elbow' quite a lot. With a bit of practice you can easily spot a swift and a swallow. Then you've got to identify the species and this gets tricky - Common Swift is best identified by being pretty much back everywhere, except a small white patch under the chin. Both the other common confusion species in most of East Africa have paler secondaries that you can see when you get a good vew - Nyanza is a bit browner, Black is otherwise similarly black. Range and season will also help - black is a highland species, Nyanza a Westhern Kenyan and northern Tanzanian - all back swifts elsewhere are almost certainly Common. Between May and early August you can be pretty sure you're not seeing a Common  too, as these are wonderful migrants.  Still, that's pretty advanced identification and I recommend visiting some well known colonies before you try and identify the other species confidently. Anyway, why do I like them so much?

Well, these are one of the most arial of any birds. They feed, sleep (like dolphins, one half of the brain at a time, flying ino the wind) and mate on the wing, and their wings are so long that they struggle to fly if they accidently lando the ground - they have to drag themselves using their tiny feet up a rock or tree to get enough height to take off again. That, in itself, is pretty remarkable. But common swifts are even more impresive than that. Feeding on small arial insects, if the weather is wet it's hard to find suitable food. During the non-breeding season, this isn't a problem - the birds just keep flying  and may cover huge distances to find suitable foragine areas. In fact, they often forage just in front of storms - a flock of swifts rushing across the plains in front of a big storm is a common indicators you're about to get wet! When they're nesting, this is a problem though - such trips take days and days. So the chicks have to survive without food for days at a time, and to do so they essentially switch off the major bodily functions and enter "torpor". Here (instead of a usual avian body temperature of around 40 degrees C), they settle on about 21 degrees and are unresponsive to external stimuli, taking several minutes to return to 'life' when a parent returns with food. The cost of this is that development is very slow - they weight about 44g, similar to a Yellow-vented Bulbul. But incubation takes about 20 days, and fledging varies from 37 days (when there's little torpor) to 57, if the chicks are in torpor a lot. That friendly Yellow-vented Bulbul, by contrast, takes a much more efficient 12-14 days to hatch and a similar period to fledge.

So, when the young birds are finally ready to fledge, they don't wait several days for their parents to return, but most set off immediately on their first flight, after sunset (there's less chance of being caught by a Hobby or similar if they make their first flight at night), which takes them straight, non-stop, to Africa. Of course, that sudden shift from being stuck in a nest, to constant flight is hard work - the young swifts prepare themselves for this insane flight by exerising: using press-ups where they push their wings down and hold their bodies completely off the ground for as long as possible - initially, only a second or two, later for longer periods. And so begins what must be one of the longest, continuous flights of any bird. On fledging, the birds leave for Africa (so these first birds might well be young ones, with adults following in a few days time), they eat and sleep on the wing the whole way down. Then once here they drift about following food, still not landing. And then come March or April, they decide to head north, back to Europe. But most don't breed in in their first year, so they keep flying up there too, perhaps checking out suitable breeding colonies. And then, come August they head back here and keep flying through the northern winter, before finally returning to Europe two years old. This time, most still don't breed, but there's some evidence they might settle in a colony and at least some of them come down to roost in their chosen nest site for the follow year. So those first flights of a young bird straight out of the nest likely lasts practically 2 years, and involves two trips to Africa and back - quite remarkable for anything I think, and sure makes up for the rather non-descript plumage! Look out for them near you, right now!


  1. One of my favourite british breeding birds!I had laugh when I was in South Africa November 2008 talking about my swifts. The south africans called them - their swifts!
    I hve decided that they are "our" Swifts as they arrive in May and are gone by the end of July usually and they are where they go for "winter" for 8/9 months!

  2. No, no, no! All the migrants are ours here in Africa! A few just go wandering. Gives me an idea for a post on the African origins of long-distance migrant birds though... (PS Hope you liked the crowned eagle post from a while back to, given your name!)