Spring Chicks

In hedgerows and on trees and cliff ledges across the country, the eggs of wild birds are hatching and new chicks are emerging – trembling, hungry and vulnerable. How do baby birds survive? Tim Birkhead explores an annual spring miracle

- By Tim Birkhead. Photographs by Getty, Alamy, Naturepl.com, RSPB Images

The image of a fluffy little chick emerging from a hen’s egg after popping open the ‘lid’ is a sugary exaggeration of what really happens. The truth is no less remarkable: simply escaping the egg is the first potentially lethal challenge of many in the young life of birds.

A bird’s eggshell has to be strong enough to support the weight of the incubating parent, but not so robust that the chick cannot get out. How is this tricky compromise achieved? The answer is through a clever evolutionary trick in which the calcium-carbonate crystals that make up the eggshell are arranged like the wedge-shaped bricks of an arched stone bridge, such that they can be safely pushed down upon (by the incubating parent), but when pushed from the inside, are less strong, allowing the chick to escape.

The eggshells of small songbirds — like our robin — are somewhat leathery, and the chick has to cut its way out, using its egg tooth, a conspicuous hardened tip of the bill. This sounds easier than it probably is. Inside the shell, the chick has to rotate several times, all the while chipping away at the shell. Then, by pushing with its feet and neck, it can lift the top, the big end of the egg, and push itself free from the shell.

Once out of the egg, the chick faces multiple threats, including cold, starvation and predators, to name but three. Survival strategies vary wildly between species. Just hours after hatching, the chicks of some bird species can run about, feed themselves and even fly, while others hatch blind and helpless and are dependent on the parents for weeks or months.