Being hatched from eggs, birds start life in a fascinating way. Eggs come in a myriad of shapes and colours, adapted to the habitats of the parent birds. For example, owls lay white, spherical eggs, while auks lay elongated, very pointed and vividly spotted eggs. Each species of bird has its own characteristic size of egg – apart from the Cuckoo.

Each female Cuckoo lays an egg adapted to the eggs of the species of bird (for example, the reed warbler) with which the Cuckoo itself grew up.

That means cuckoo eggs can vary in terms of size and colour, and spots or no spots!

The illustration shows a female Cuckoo removing an egg from the nest of the host bird and laying its own instead.

In reality, the eggs develop in the female bird for a fixed number of days.

During that period, in many bird species minor haemorrhages occur in the uterus, which are ‘baked’ into the eggshell during the final days before the egg is laid. This results in distinctive spots and patterns for each bird species, though they always vary slightly from one bird to another. Colour, speckles and patterns are totally adapted to the place where the eggs are laid – frequently to provide as much camouflage as possible. There are many egg thieves, so the eggs need to be well hidden.

The eggs in the hands are drawn in natural size. On the ground are large-scale copies of the same eggs. The eggs are tough and can withstand weather conditions.

All eggs are secured to the ground so they cannot move.