Chicks take the heat, end up girls
Temperature influences the sex of birds, not just reptiles, researchers have shown for the first time.
Australian researchers Dr Ann Göth from Sydney's Macquarie University and Dr David Booth from the University of Queensland studied the unusual habits of the Australian brush or bush turkey (Alectura lathami), after a tip-off from an Aboriginal elder.
They say brush turkeys are the first known birds to regulate the sex ratio of their chicks using temperature. But they are thought to do it in a different way to some reptiles.
The brush turkey is unusual as it belongs to a group of 22 bird species known as megapodes that do not sit on their eggs. Instead they use environmental heat sources such as composting leaf litter.
Göth said after the female lays the eggs the male tends the composting mound using a temperature sensor in his upper beak to keep the mound between 30 and 37°C.
"Each day during the nesting season from July to February he takes a small amount of soil in his beak and checks the temperature," she said.
"If it is cold he will add more leaf litter and if it is too hot he will open the top of the mound to cool it down."
Göth found equal numbers of male and female chicks hatched at the average mound temperature of 34°C. But more males hatched when the mound was a lower 31°C and more females hatched at a higher 36°C.
Göth said unlike reptiles, brush turkey incubation temperature did not determine the sex of an egg but rather affected which eggs would survive.
"We know in reptiles temperature determines the sex of an egg after it is laid but the sex of a brush turkey is determined by the time it is laid," she said.
Göth studied nest temperature after an Aboriginal elder in the Atherton tablelands of Far North Queensland told her there were more female chicks following a hot nesting season and more males after a cold season.
"The Aboriginal people have been aware of a connection between incubation temperature and brush turkey sex for a long time," she said.
Other Australian megapodes include the mallee fowl and orange-footed megapode that use similar incubation methods as the brush turkey.