Have you ever wondered how birds are able to perch on a branch and go to sleep without falling off? It’s all down to a special tendon-locking mechanism that they have. It runs from their leg muscles down to behind the ankle joint and attaches to the toes. When the bird lands, it bends the leg at the knee and ankle, automatically pulling taut the tendons which in turn causes the toes to curl inward. When they settle to sleep the weight of the bird helps maintain the tension, allowing them to rest or sleep without the danger of falling. To release the grip, the bird just straightens the leg which disengages the locking mechanism.

Even more amazing is the creation of a chick inside the egg. There is no external support so everything to make the chick grow is in the egg itself. The calcium from the shell is absorbed to make the bones, making the shell very thin towards the final stages of incubation. Most of the chick is created from the albumen (the white of the egg) and part from the yolk. The yolk varies according to the species. If the chick is able to feed itself when it hatches out, there is a large yolk, most of which is absorbed into the stomach of the chick as it hatches. This gives it enough sustenance for 24 hours while it learns to feed itself. A chick that is fed by parents only has a small yolk as it doesn’t require this support.

When ready to hatch, baby birds like this duckling almost fill the egg (Image: Supplied)

When ready to hatch, the chick will fill the egg except for the air cell which is at the blunt end of an egg. The chick’s head is tucked under its wing and on the end of its beak there is a special egg tooth, visible for a short while after hatching. Muscles in the neck of the chick start to spasm and this will cause the egg tooth to pierce the membrane of the air cell and from that time on, the chick is now breathing air. The egg tooth then pierces the shell, and the chick has to rotate around inside the shell until it has made piercings all around the top of the egg, allowing it to finally emerge from the shell. By this time the chick is exhausted but will recover as it dries.

Incubation time varies according to the species – a robin is only 12-14 days, a barn owl 32-34 days, ducks are usually 28 days and swans are 36 days. Incubation for a heron is 30 days and yes, they do nest up in trees! Domestic chickens are only 21 days and because the chicks feed for themselves when they hatch, the yolk of the egg is large. Which is why we like eating them..

secretworld.org