canberrabirds

Fw: Kooaaa! It's a kookaburra!

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Subject: Fw: Kooaaa! It's a kookaburra!
From: "Tony Lawson" <>
Date: Thu, 15 Oct 2009 19:33:44 +1100
I followed Geoffrey's advice and sent this to myself first to check its size - 68kb.
 
Tony
 
PS Although I made a faux pas sending the large Cocky file, it seemed to be appreciated by quite a few people.  Old news to some (apparently including my wife) but not to me and quite a few others.  But apologies again to those who were inconvenienced.
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By Rachel Sullivan

Springtime is no laughing matter for kookaburra chicks as they fight for survival in the family nest.

The largest members of the kingfisher family, kookaburras are native to Australia and Papua New Guinea. Australia is home to two of the four species: the colourful northern blue-winged kookaburra (Dacelo leachii) which is found in the country's north, as far south as Broome on the west coast and Brisbane on the east; and the iconic laughing kookaburra (Dacelo novaeguineae), which is found all along the east coast, from the Eyre Peninsula to Cape York.

"[Laughing] kookaburras were also successfully introduced to Perth, Tasmania, Flinders and Kangaroo Islands," says Dr Sarah Legge, who studied laughing kookaburras for her PhD and is now the lead ecologist with the Australian Wildlife Conservancy.

"They were also introduced to Fiji at the start of the 20th century but the experiment was short-lived ? they had all disappeared within 25 years. Attempts to introduce them to New Zealand were slightly more successful, with small populations still found in the North Island," says Legge.

The two species are easily distinguished by their laugh and the colour of their eyes. The blue-winged kookaburra has a maniacal screech compared to its much more jovial cousin, and tends to have a staring, white eye while laughing kookaburras' eyes are brown with a brown patch of feathers behind the eye.

Fact file

When:September to January

Where: Northern blue-winged kookaburras are found in the tropical north as far south as Broome on the west coast and Brisbane on the east. Laughing kookaburras are found all along the east coast, from the Eyre Peninsula to Cape York, as well as introduced populations in Perth, Tasmania, Flinders and Kangaroo Islands.

Other information: Where their ranges overlap, blue-winged and laughing kookaburras compete directly for food and other resources. Experts think that although they share a common ancestor, the two species evolved in isolation, and came together only recently ? in geological time anyway.

Family life

Although kookaburras require trees with nest hollows or arboreal termite mounds for breeding, most of the year they roost in family groups, snuggled up together on a branch.

"From the amount of noise they make they appear to be everywhere, however the number of kookaburra families living in an area depends on the productivity of their territory," says Legge.

"In a high productivity area like Victoria's Dandenongs there is a group every 40 hectares; but around Canberra, where the land is less productive, each group needs around 2000 ha of territory."

Kookaburras eat a range of prey, including small reptiles such as lizards and snakes, insects, worms, snails, frogs, rodents and even the occasional small bird. "Because they are such big birds, with large beaks, they are not very agile when flying so only rarely catch prey on the wing," says Legge.

"Instead they focus on catching prey moving through the leaf litter. They either watch from a branch or sit very still on the ground, watching for telltale movement.

"Then they strike, and carry their prey back up to the tree where they bash it against a branch to kill it, and soften it before throwing back their head and swallowing." Indigestible bones and hair are later regurgitated in pellet form.

Legge says that ranges may be smaller in urban areas because clearing exposes leaf litter and gardens provide lots of good habitat for invertebrates and small lizards, but they are limited by the number of nest hollows available for breeding. "They can withstand some modifications to their habitat, but are limited by this fundamental need."

The bigger the better: this fat little laughing kookaburra chick has a survival edge over its siblings (Source: istockphoto)

Survival of the fittest

Kookaburras mate for life and live in close family groups, comprising two adults and the older siblings from previous breeding seasons, which remain for up to three years to help their parents incubate the eggs, and feed and protect the chicks and fledglings before moving on to nests of their own.

'Kookaburras are unusual because they exhibit two extremes of social behaviour ? as older birds they are altruistic helping the parents to raise their siblings, but as chicks they actively try to kill each other.

"From an evolutionary perspective it's a silly thing to do," says Legge, "but it's a resource issue."

The mother lays three eggs, but about 50 per cent of the time there isn't enough food available to raise all three chicks, she says. "There is only a 10 per cent chance of hatching failure, so if all three do hatch, it is best for the group that one hatchling is disposed of before too much time or resources are invested in it ? usually it's all over in the first three days."

Legge says that while the parents allow the chicks to sort out between themselves which one is the feeblest, the mother actually controls the siblicide through controlling the time between hatchings.

"Hatching rates vary, which makes it fairly easy to pick who the winners and losers will be in a battle between nest mates. They can all hatch within a 24-hour period or up to 72 hours apart.

"In addition, the third egg is usually the smallest, and the first chick to hatch is male, the second female. But females grow faster, which makes the dominance hierarchy unstable and leads to more fighting."

If it's taking too long, the mother will take drastic steps: she will brood the chicks, then step back and watch them fight until they become torpid with cold, then start the process all over again.

"It's hard for the mother to assess which chicks are the strongest, but if she lets them fight it out the matter is quickly resolved."

While it sounds unnecessarily cruel, Legge says that if the family tried to raise three chicks they might all be stunted, reducing their chance of survival anyway. "The goal is to produce big, fat, healthy chicks."

Older siblings help their parents do this by helping to brood the eggs, and feeding and protecting the nestlings. "This reduces the workload for the parents, helping them to live longer and produce more clutches of eggs," Legge comments. "It helps ensure the survival of the young and also teaches the older siblings how to feed and raise their own families, meaning that more genes will be represented in the next generation."

Some helpers are more diligent than others, however. "Daughters tend to arrive at the nest with food, and make a big fuss over what they have found then quietly eat it themselves when no-one is looking," Legge laughs. "They are bigger than the males and not as agile so it's probably harder for them to find food" adding that it's also more energy efficient to be small, so they need to eat more to keep going.

Laugh, kookaburra, laugh

Most Australians are so familiar with the kookaburras' raucous cacophony that we barely notice their dawn and dusk calls.

"The point of the morning call is not entirely clear," says Legge, "although it is likely to be a territorial proclamation saying 'we're still here, we survived the night, don't mess with us'." She adds that calling frequency increases when the nestlings fledge.

While their loud laugh that can be heard over long distances and is best known, kookaburras have a range of calls that are used at different times.

The year-round laugh song advertises territorial ownership, as does the chuckle, which is also used to find missing family members. Both species' laugh song is similar in the way family members join in at different times - making the song seem to rise and fall - but the laugh song of the blue-winged kookaburra sounds maniacal or insane compared with the more jovial laughter of the laughing kookaburra.

The chuck is used in breeding, and the squawk is used to beg for food or is a sign of submission to aggressive family members, while the softer, more intimate croon or soft squawk is used in courtship and to calm the breeding female.

The cackle signals aggression and an imminent attack, while the kooaa is used year round as a warning to the group.

At last, we know what  the kookaburra is laughing about.

Source: http://www.abc.net.au/science/articles/2009/10/14/2712935.htm 

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