When the pandemic hit, the song of birds offered joy and hope. The author of a new book recalls that glittering spring and explains the science behind bird calls and how to identify them

It’s six in the morning and still dark, 24 March 2020. I wake early and, knowing the children will soon be up, decide to steal half an hour’s solitude in the park. From the dense latticework of trees and shrubs that clothe the wooded slope comes a constant scuttling through dead leaves. The darkness is awake and vigilant; there’s the warning tik-tik of an invisible robin from the bushes, and then the next second it appears on the path. Each individual movement of the bird, each wing-flick and pivot, is brisk and definite yet the overall impression is one of nervousness and indecision. It leaps round once more on the spot, then flits back into the darkness.

From close by comes a blast of song from a wren. Its harsh trill is like coarse twine zipping over a flywheel. The air is cool, not cold, and smells deliciously of earth and moss. There’s a sudden disturbance from the deeper shade, and a blackbird comes careering out with a mad clatter and pauses, alert, on the great arm of a beech tree. It’s evidently agitated. It flicks about the bough, dipping then raising its wings, and tilting its head all the while in response to something I can’t sense. After a few seconds of this twitching the bird seems to experience some sort of inner resolution, and, as the first beam of grey light wakes the colours of the tree, it raises its head and lets out a quiet phrase of song. Spring has arrived.