Andrada Dumitrascu, Hannah McLeary and Lucas Leaf, of Balclutha Primary School, asks :-
Why are eggs different shapes and colours, and how do the chicks get out?
Alex Davies, a veterinarian at Massey University, responded.
So that the developing chick's heart can work properly, the hen has to turn the egg regularly. If the eggs were round, they might roll out of the nest. If the egg is oval and more pointed at one end that the other, it will roll in a circle. The best shape of an egg will depend on the kind of nest.
Eggs contain excellent food for the chick. But other hungry animals also find eggs nutritious. It's an advantage for the bird if eggs are hard to find. White eggs are rather obvious but these are unnatural. Most eggs in nature are grey, brown, blue or speckly combinations. This makes them merge with their surroundings. The gland that makes the shell has to get the colour right, and print on the pattern. The bigger the animal, the longer it takes to develop. For big eggs, the time between laying and hatching should be longer. A hen's egg weighs about 60 g, and is incubated for 21 days. Kiwi eggs weigh about 450 g, and the female is glad that her mate will keep it warm for 11 weeks. This is remarkable because even an ostrich with an egg weighing 1400 g only takes 42 days to develop before it hatches.
Baby birds run around soon after hatching, and they are also active before hatching. Strong head and neck movements crack the shell. Also, the beak of some newly hatched birds has a hook that helps break the shell.