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How brush turkeys keep their nest at exactly 33 degrees

Anthony Sharwood, Thursday November 7, 2024 - 15:48 AEDT

Thirty-three degrees. That's the magic temperature at which Australian brush turkeys need to maintain their eggs for hatching, and they regulate the heat in their nests in a really unusual way.

If you live on Australia's east coast from the tropics of Cape York all the way down to the Illawarra region of NSW (just south of Sydney), you'd be well familiar with these adaptable avians, which are also known as "bush turkeys" or "scrub turkeys".

In the early 20th century, they almost went extinct, with numbers dipping to a catastrophic low during the great depression of the 1930s when they were widely hunted for food.

Image: Why did the brush turkey cross the road? Source: John Martin.

But brush turkeys are now protected in both Queensland and NSW, and in recent decades their numbers have exploded as they've successfully colonised urban and semi-urban areas, becoming fixtures in many Sydney suburbs.

Scientists were already surprised when brush turkeys started moving into suburbs with high vegetation cover, or which lie adjacent to bushland. But when they moved into heavily built-up areas, they were really taken aback.

That’s because brush turkeys need plenty of materials like plant matter and soil in order to build mounds that protect their nests and keep them at that ideal temperature of 33°C.

Building mounds is very rare bird behaviour. Australia has approximately 850 bird species, but only three build mounds to protect their eggs. Those would be the malleefowl, the orange-footed scrub fowl of northern Australia, and the brush turkey.

"This is a prehistoric nesting technique,” bird expert and wildlife consultant John Martin tells Weatherzone.

"There are almost 10 thousand bird species in the world, and probably about 9950 use their body temperature to incubate the egg. But brush turkeys do it by opening the mound to let heat out and closing it to trap heat in."

Image: That is one serious mound. Source: John Martin.

Brush turkeys have highly sensitive heat sensors inside their upper bill. If the temperature of the mound is too high or low by even a fraction of a degree, they'll rake material on or off it as required.

It's full-time work and it’s all the male's job. The female lays up to 24 eggs, then leaves the hard yakka of mound maintenance to hubby.

"They are industrious and tenacious, tending their mounds from sunrise to sunset," Martin says.

"Sometimes they make their mounds in gardens and people try to rake them away. When that happens, they just rebuild it. We’ve put cameras on mounds and captured a whole heap of different animals try to eat the eggs – from goannas to foxes and other birds and animals. But they’re very resilient birds."

Perhaps it's that resilience and work ethic which have led to the success of brush turkeys joining native species like ibis and cockatoos as thriving urban dwellers.

Their varied diet is another key survival asset. Brush turkeys will eat anything from insects, snails and reptiles to fruits and seeds. They’ve even developed a taste for pet food left out in bowls.

First baby Brush-turkey we’ve spotted for the season (in Sydney)! Are you seeing these Bush-Babies?? Please report sightings using the Big City Birds app https://t.co/EVSkqNrVvH@BigCityBirds1 @Sydney_Science pic.twitter.com/DvfCUHGzys

— Dr John Martin (@Wingtags) October 30, 2024

While it's a scientific fact that brush turkey chicks are super cute (see above), one thing adult brush turkeys don't do so well is fly.

"They can fly but only just," Martin laughs. "They run, then do a bit of a flap and then get a few metres up into a tree, but they don’t soar or glide. And when jumping out of a tree, they are not like any other bird that you have seen!"

That inability to take to the skies makes the spread of the brush turkey in recent decades all the more remarkable. Somehow, they’ve avoided traffic and other hazards as their habitat expands.

So the next time it's a 33-degree day, ask yourself how you'd go maintaining that exact temperature by moving lumps of soil and plant litter with your beak – and doing it from dawn till dusk for a seven-week incubation period. These aren’t Australia’s most beautiful birds but they’re definitely among the most admirable.

Image: Who knew it was such a hard-working bird? Source: iStock.

And for those wondering, John Martin told us that there's no evidence that the southward migration of brush turkeys in recent decades is related to climate change (although no comprehensive studies have been done on this).

They're simply reclaiming territory that once was theirs, even if they have to share it with suburban humans and their pets.

If you see a brush turkey for the first time in your area, or even one that's been around for a while, scientists would love it if you reported it on the Big City Birds app so they can monitor the progress of wild species that have moved into urban areas.

- Weatherzone

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