There is great excitement in the bird world as the breeding season begins

IN FLIGHT: Spring marks the beginning of the breeding season for Australian cuckoos such as the female Eastern Koel, pictured.
IN FLIGHT: Spring marks the beginning of the breeding season for Australian cuckoos such as the female Eastern Koel, pictured.

Its spring and there is great excitement in the bird world as the breeding season begins.

That also means that the cuckoos are returning and their various calls are already audible in the local area.

There are 12 species of cuckoo in Australia, with the largest, the Channel-billed Cuckoo and the Eastern Koel, migrating from Northern Australia each year.

These are the two birds that keep us awake with their constant calling both day and night, during the breeding season.

Some of the other smaller cuckoos commonly seen or heard locally are Shining Bronze Cuckoo, Fan-tailed Cuckoo and Horsfield's Bronze Cuckoo.

Cuckoos do not make their own nest, but rather lay their eggs in other bird's nests and then leave the host bird to raise the chicks.

They are brood parasites, an evolutionary adaptation that is endlessly fascinating and sometimes cruel.

The cuckoos cannot survive unless they trick the host bird into accepting their eggs and raising the chicks, that often grow much bigger than the adoptive parent.

The birds targeted to be hosts are Red Wattle Birds, Magpie-larks and Figbirds and smaller birds such as Fairy-wrens and Gerygone.

The eggs of some cuckoos have evolved to match the eggs of the host species, which fools the host bird.

The cuckoo chick fights hard to survive, often pushing the hosts chicks or eggs out of the nest, removing the competition for food.

An enormous amount of energy is expended by the host parents, trying to satisfy the hunger of their large cuckoo babies.

However, some bird species, such as Superb Fairy-wrens, have evolved to reject cuckoo eggs.

Research at Flinders University in South Australia has shown that Fairy-wren mothers sing a special tune to their eggs before they hatch.

BIRD LOVERS: Some of the other smaller cuckoos commonly seen or heard locally are the Shining Bronze Cuckoo and Fan-tailed Cuckoo, pictured.

BIRD LOVERS: Some of the other smaller cuckoos commonly seen or heard locally are the Shining Bronze Cuckoo and Fan-tailed Cuckoo, pictured.

The tune contains a special note that acts like a password and is learned by the embryonic chick.

If cuckoo eggs are deposited into the nest after the fairy-wren eggs, the embryo cuckoos don't have time to learn the password.

This password is then incorporated into the begging calls of the fairy-wren chicks after they hatch, indicting which chicks to feed.

Young cuckoos do not imprint on their host parents but instead have an understanding they are different and are drawn, instinctively to the call of their own species. When it is time to leave the nest, they form flocks with other young migratory cuckoos and return north.

For more information or to learn about other species of Australian birds, visit the Hunter Bird Observer's Club website at hboc.org.au/

Research at Flinders University in South Australia has shown that Fairy-wren mothers sing a special tune to their eggs before they hatch