However, they're territorial, and this one was hunting a tree I walked past every day. It occurred to me that if I walked by often enough, and had my camera ready each time, there might at some point be another chance. Then I found myself thinking that each morning's no show as I passed the pollarded lime tree would be a tiny disappointment, now that I knew the treecreeper was there, just out of sight. And I put my camera away and stopped hunting the skulking and insectivorous treecreeper. I hear it often enough though; that distinct high delicate fluting whistle (you can hear it here).
In September, the birds begin to wake up after their summer moult, and sing again. New adults encroach into mature territories, older birds falter a little, trying out their rusty voices. Later it'll get serious, and they'll start to practice, fight and mark out their spaces along the tow-path. But for now it's sheer exuberance; food is plentiful, their feathers are fresh, and the trees along the river are warmed by the last of the summer sunshine.