Summer westerlies blow across the open fields, and swallows and martins know where to go. Though they are genetically close cousins, tripping off the tongue as a matched pair, such tricky conditions see these birds feed in quite different ways.
House martins play the role of day-flying bats, but without the onboard hi-tech of echolocation. They flock where insects swarm and see what is invisible to us. A dozen or more are carving the air behind a long, bushy shelterbelt, in the lee of the wind, plaiting each other with flight paths that keep them bound together and apart. Here there may be midge leks or an emergence of flies from the trees and bushes, the insects shielded from turbulence. Either way, the martins are seizing their moving opportunities with open beaks.
I stand before the trees and the martins cut in front and behind me, pure white rumps blazing as bum beacons. Their flight is all effort and rest, a frenetic beating of wings to rise, then a descending swoop. A diligent scientist once recorded 49.9% of house martin flight as flapping time and, apparently, food is usually taken on the up. Up and down they go until eventually they melt away from the far end of the belt.
Further down the path is a flower-filled fallow field where a thousand cowslips bloomed in the spring. The ground must right now be releasing a flush of insects, for a flock of swallows flies to and fro, skimming the tops. They chase with steady, shallow beats, the merest flicks that propel them at speed. Last week I saw one over a close-mown stately home lawn, its wingtips dipping no more than a few centimetres above the ground. Thirty times a minute it risked a strike, a fall, a broken wing, certain death, yet still it stayed low.
At last, these swallows, like the martins before them, are sated, and depart, presumably to their nests. Throat pouches must be full with balls of insects mixed with saliva. Will their 10-minute foraging trips be enough to fill four or five hungry little mouths?
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