Swifts are among my favorite birds, for several reasons. I like their swept wings and tails, and I like their extreme aerial lifestyle. I like that they eat bugs, that would otherwise bug me.
In the early Summer, under towering thunderheads, swifts criss-cross, 30m high, and if you re-focus your eyes, you’ll see more are 100m high, and more 200m high... until they’re out of sight.
What are the swifts doing there?
They aren’t there (just) for fun. They feed on small insects and spiders.
Which means, between us and the giant weather formations, among our feathered cousins, but invisible to us, are numberless hordes of little bugs.
What are the bugs doing there?
Why would little bugs fly in such numbers, up into thunderclouds? Doesn’t that seem like a good way to lose your little life?
The insects and spiders are up there, because the air rising high into the thundercloud provides them an excellent means of transportation. When moving by their own means is very slow, a thundercloud could transport them hundreds of kilometers. Sure, most of them probably die on the journey, but their numbers are their strength and protection. Enough of them land in fertile new areas to make the risk worthwhile to their species.
Swifts are members of the bird family apodidae, which means “footless”. They cannot walk: if you see a swift on the ground, it is dead, or dying. Instead of legs, they have little hooks, with which they can cling onto a rock or brick face.
Swifts feed, sleep, and mate on the wing. They rarely need to land. But there is one thing all birds do, which is not practical to do in the air: they lay eggs. They have to make a nest.
Swifts and swallows have similar-looking swept wings, forked tails, and wide bills. Despite that, they are not closely related.
Swallows belong to the same bird family as sparrows, while swifts are thought to be distantly related to hummingbirds.
They both feed on flying insects, and therefore, their bodies are optimized for fast and agile flight. It is a case of convergent evolution.
Swifts tend to hunt higher in the air, above 4m. Swallows tend to zoom over open fields and ponds, often under 1m high.
The English name for a swift is more often an adjective: swift, meaning speedy. Formerly, in Old English, the word had a verb form, meaning “revolve”, and that word also gave rise to the modern English verb “swivel”.
Swifts are indeed speedy, and they do swivel a great deal when hunting.
In some other languages:
French: martinet (from the name Martin, a diminutive
of Latin Marcus, meaning “hammer”),
Dutch: gierzwaluw (vulture-swallow),
German: Mauersegler (wall-sailor),
Italian: rondone (patrol, make the rounds),
Spanish: vencejo (may derive from a word meaning
hook or claw),
Chinese: 雨燕 (rain-swallow)
I was sitting on the patio of a little restaurant, when I noticed several dragonflies crisscrossing over my head. Hunting. And then I focused my eyes higher in the sky, where dozens of swifts were crisscrossing. Hunting.
Another evening, I watched bats criss-crossing a little pond under a full moon. They were hunting insects, too. And on warm Summer afternoons swallows criss-crossing a grassy field, again, hunting. All of these different creatures of the air behave similarly, in their hunt for crunchy food.
The common swift of Europe is a migrant. They spend Summer all over Europe, and they winter in southern Africa. Birds are nothing, if they ain’t mobile.
Swifts form hunting parties of four to eight individuals, which circle in tight formations about treetops, screeching loudly.
I once experienced that screech head-on. I was just walking down a residential road, when a single swift broke off from its party, and zoomed down the same street, beneath the trees, toward me. At a distance of about 5m from me, it let loose a screech that penetrated my head and overloaded my eardrums, and rang for a while after. (The bird immediately swerved, so we did not collide.)
The sound is vastly louder head-on, than it is when heard from the side. It is very directed.
A sound so loud is unnecessary for communication, especially among birds flying in close formation in daylight.
The screech has to do with a mode of hunting, somehow. One idea (my own, which I’ve been unable to confirm anywhere), is that it may be a form of echolocation, as is used by bats and whales. (Maybe their prey is too small for them to see from a distance.) Another idea is that the sound stuns the prey, making it easier to nab. It certainly stunned me.