For years the cuckoo was a sound, not a bird. The call carries a long way and seems to move about, coming from different directions, so you never quite fix where it is. Then a couple of weeks ago, there it was, sitting on a wire in the afternoon sun.
I was lucky it was there at all. Adult cuckoos leave early, most are gone from northern Sweden by the end of July, so this one was a straggler hanging on into August.
Where they go was a mystery for centuries. The cuckoo turns up, calls for a few weeks, then vanishes, and for a long time nobody could say where to. One old idea was that it didn't leave at all but turned into a hawk for the winter. They do look alike, and Aristotle weighed that up before throwing it out. The likeness still works on small birds, though, which will mob a passing cuckoo as if it were the sparrowhawk it isn't.
The BTO has been tagging cuckoos since 2011, mapping the whole trip to the Congo and back. It's also how we know how much trouble they're in, UK numbers are down by a third since 1995. You can follow this year's birds crossing the Sahara right now.
By the time they reach the Congo they've gone quiet. The cuckoo only cuckoos here, on the breeding ground in spring. In Africa it doesn't call at all.