Excerpt from Helen Macdonald's 'Vesper Flights'

I worked at a falcon-breeding centre in Wales. In one room were banks of expensive incubators containing falcon eggs. Through the glass, their shells were the mottled browns of walnut, of tea-stains, of onion skins. ... We weighed them each day, and as the embryo moved towards hatching, we'd candle them: place them on a light and scribe the outline of the shadow against the bright air-cell with a soft graphite pencil, so that as the days passed the eggshell was ringed with repeated lines that resembled tides or wide-grained wood. But I always left the incubation room feeling unaccountably upset, with a vague disquieting sense of vertigo. It was a familiar emotion I couldn't quite name. I finally worked out what it was one rainy Sunday afternoon. Leafing through my parents' albums I found a photograph of me a few days after my birth, a frail and skinny thing, one arm ringed with a medical bracelet and bathed in stark electric light. I was in an incubator, for I was exceedingly premature. My twin brother did not survive his birth. And that early loss, followed by weeks of white light lying alone on a blanket in a Perspex box, had done something wrong to me that echoed with a room full of eggs in forced-air boxes, held in moist air and moved by wire. Now I could put a name to the upset I felt. It was loneliness.

That was when I recognised the particular power of eggs to raise questions of human hurt and harm. That was why, I realized, the nests in my childhood collection made me uncomfortable; they reached back to a time in my life when the world was nothing but surviving isolation. And then. And then there was a day. One day when, quite by surprise, I discovered that if I held a falcon egg close to my mouth and made soft clucking noises, a chick that was ready to hatch would call back. And there I stood, in the temperature-controlled room. I spoke through the shell to something that had not yet known light or air, but would soon take in the revealed coil and furl of a west-coast breeze and cloud of a hillside in one easy glide at sixty miles an hour, and spire up on sharp wings to soar high enough to see the distant, glittering Atlantic. I spoke through an egg and wept.