Telling the sex of birds like parrots is not easy. You cannot tell by looking. To make matters worse most of the world's bird species are monomorphic - the male and female look identical.

Until recently only a handful of tricky tests, or traumatic surgery, could be used to tell the sexes apart. But thanks to scientists at Oxford University help is at hand.

Their technique was adapted from methods used to extract genetic material from frozen mammoths.

The scientists have identified a key gene that occurs only in females and can be tested for in moulted feathers and droppings. The gene is common to all birds, except ostriches.