In natural history, it is easy to notice a first for the year, but to be mindful of the last is more difficult. I know that the house martins are gone, yet their going from our village entailed an unremarkable dwindling of sights and sounds, but slowly, like a loss of moisture in a puddle.
I did have one memorable sighting last week in the Yare valley. Over Blackwater, about 40 were pooled above a poplar plantation and in and out of their midst swirled a single lost swift. The martins were smaller, busier, each one with a swept-back wing silhouette, which, depending on the way it turned, was shaped like a broad smile, or frown.
They were feeding in a manner that entailed much even soaring, then passages of wingbeats of about 15 flickering strokes in bursts of 1-3 seconds. In those moments of intensity, the birds would steeple higher, catch their fly, and then fall, resuming the steady-state evenness of the glide. I estimated 40, but only a dozen birds were visible at any moment and the rest were implied by an elastic net of dry buzzing notes that are the perpetual atmosphere in which house martins pass their lives.
It seemed to me that it was the outriders that vocalised most, reassuring themselves of contact, but providing the loose, mobile web of calls with which all could keep company. And this sound, as simple as dried grass and as modest as insect stridulation, is the thing they take with them to Africa, and which I shall miss most.
Since this bird eats only invertebrates, it is a call made of insects, but it is also much more. For house martins eat what is known as aerial plankton and the birds will return to Europe from Africa only when these tiny airborne organisms reach a critical mass in the air above our country. As the light diminishes, as warmth fades, as our hemisphere turns at an angle of 23.4 degrees away from the sun, so the calls go south. Think, then, of the house martins’ warm envelope of dry notes as nothing less than the music of our planet turning in space.
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