Channel-bills go cuckoo in spring

You know it's spring when you're woken in the early hours of the morning by the deafening calls of channel-billed cuckoos looking for love.

Say 'cuckoo' and a finch-sized bird popping out of a wooden clock every hour probably comes to mind. But, at between 58 and 65 cm tall, with a piercing stare, channel-billed cuckoos are the world's largest parasitic bird.

Weighing as much as a kilo, adult birds are light grey with brown bars on their tail, with males slightly larger than females. They have a sharply curved, toucan-like bill, and an unmistakeable crucifix silhouette in flight.

Also known as stormbirds or rainbirds, their unearthly nocturnal call wakes neighbourhoods from the tropics right down the east coast of Australia in spring as they wing their way from Papua New Guinea looking for love.

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Southern migration

Channel-billed cuckoos spend the Southern Hemisphere winter in the Indonesian islands of Sulawesi and the Moluccas, the Papua New Guinea mainland and islands of the Bismark Archipelago off its north eastern coast, heading south to Australia from late August, usually arriving in their final destination in early-mid September.

While in Australia they live in tall open forest areas, along watercourses and rainforest streams, especially where there are lots of fruiting plants, says Dr Richard Major, an ornithologist and ecologist from the Australian Museum, who coordinated the Birds in Backyards project for several years.

"Most are big fruit eaters, favouring native figs which they pluck from the tree with their bills, as well as other native fruits, some seeds, insects and even baby birds," says Major.

Although not generally a nocturnal bird, channel-billed cuckoos are notorious for calling all night. They make the same ruckus in flight, which Major says probably helps them stay in touch with other birds in the area as well as helping them stake their claim to a particular territory, but when it comes to mating, they tone it down.

"The male tenderly feeds fruit or insects to the female while they 'talk' to each other in little, low guttural calls," he says. And when the time for conversation has passed, mating is a civilised transaction: the female squats low on the branch and spreads her wings; the male mounts her and she takes the food.

But it is not yet known at what age the cuckoos start breeding, whether they return to the same area in subsequent years or whether the cuckoos' migration stops only when they find a likely, unattended nest.

Fact file What: Channel-billed cuckoos Scythrops novaehollandiae When: September - February/March. They are usually in Sydney by 12 September. Where: They are most common in Queensland and Northern NSW, but can be found across the top end to the Kimberley in WA, and down the east coast to Victoria, and occasionally inland along Lake Eyre drainage routes.

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A common sight

Australia 'plays host' to 13 cuckoo species, but channel-billed cuckoos have become much more common over the past 30 years, says Major.

"The Birds of Australia Atlas surveys were done around 1984 and 2003 and in that time, the incidence of cuckoos being sighted and reported doubled," says Major.

The increase in channel-billed cuckoos could reflect an increase in the abundance of their host species, says Major.

Channel-billed cuckoos commonly parasitise pied currawongs, Australian ravens, little crows, Torresian crows, magpies, magpie-larks, collared sparrowhawks, and white-winged choughs.

"Around Sydney, for example, the cuckoos mainly parasitise currawongs. Until the 1960s, currawongs' breeding stronghold was in the Blue Mountains; they weren't found breeding in Sydney, only visiting in autumn and winter to feed," says Major.

"Urban areas provide lots of food in the form of introduced fleshy fruited plants like privet, lantana and blackberries, which the currawongs have assisted in extending their range as they help spread the seeds of these plants.

"Currawong populations are now present year-round in Sydney, breeding prolifically, and the channel-billed cuckoos are playing catch-up, responding to the abundance of their favourite host," he says.

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Nest invaders

Once they've mated, it's time to find some unsuspecting surrogate parents to raise the cuckoo chicks.

The adult female cuckoo lays one or two glossy, dull white to reddish brown, lavender spotted eggs in the host's nest, although Major says dissected birds have revealed up to four developing eggs, so she may lay in more than one nest.

The female may damage or expel the host's existing eggs in the process of laying, then hands over responsibility for incubating and raising her chick to the host birds.

"Most cuckoos are 'ejectors', that is the first thing the blind cuckoo chick does after hatching is to push the other eggs out of the nest, but channel-billed cuckoos don't do this.

"Instead, the mottled brown chicks grow much faster than the host's chicks, demanding the lion's share of the food, usually starving the other chicks."

Major says there is some anecdotal evidence that the host chicks don't take this lying down, and battle fiercely for their share, at least in the early stages.

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Gigantic mystery

For such a large, noisy bird, surprisingly little is known about channel-billed cuckoos, and a lot of knowledge is being gained through amateur observations, says Major.

"So little is known about them that the public's observations such as through the Birds in Backyards program is key to finding out more about them and their habitats," he says.

Bruce Thomas, a Coffs Harbour-based photographer, observed a pair of currawongs raising a channel-billed cuckoo over a period of two months in 2008. The nest was only six or so metres up a tree, almost at eye level from his deck.

"We had found two dead, partially hatched currawong chicks on the ground under the nest, and assumed that the remaining egg was another currawong until this gigantic chick stood up in the nest," says Thomas.

"For about two months it called noisily for food all day, screeching raucously if it was left alone for more than about five seconds. The parents were forced to constantly fly backwards and forwards from a nearby grapevine trying to keep up with its demands.

"They obviously didn't recognise it as not being their own and wore themselves out trying to satisfy its hunger, but there was a time when it stood up in the nest and threw its wings out, which really seemed to frighten the currawongs.

"It was like an eagle looming over a sparrow," he recalls.

By the time it was ready to fly at a couple of months, it was too large to fit in the nest, and spent the days hopping around the branches building up its strength, he says.

"The currawongs didn't seem to actively try to teach it to fly; it seemed to learn on its own."

Once it was out of the nest, Thomas says it started to call and one of the adult cuckoos, which had presumably remained in the area reappeared.

"As soon as the chick could fly, the adult cuckoo flew down and sat on the branch next to it. They had some conversation then they both took off," presumably eventually working their way north across the Torres Strait.

Neither the channel-billed cuckoos or the currawongs returned to nest again.

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