Country diary: The house martins are gone for another year. But they’re not forgotten | Ed Douglas

Lockerbrook, Derbyshire: Last week they were here, now they are not. Yet the details of their epic migration are still a mystery to us The sudden absence of something, even though you know it’s coming, can dent the heart a little. The Japanese, inevitably, have a phrase for it: mono no aware , the pathos of things , and by things, in this case, I mean house martins. Last week I had stood in the same spot, looking across the same valley. The weather then was much the same as it was today, low‑angled sunlight through patchy cloud lighting up the yellowing birch leaves and bronzing moors