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Talk about egging your siblings on. Baby turtles communicate before hatching to coordinate their arrival into the world.

Australian river turtles () lay eggs in a hole in a sandy riverbank. Eggs at the cooler base of the nest develop more slowly and should hatch later than their warmer brethren at the top, says Ricky-John Spencer at the University of Western Sydney, Australia 鈥� but all eggs apparently hatch together.

To confirm this, Spencer took eggs from the same clutch and held half at a low and half at a high temperature for two-thirds of the incubation period. When he reunited the eggs for the final third, the formerly cooler eggs used the time to play catch-up so that all eggs hatched together.

The eggs might communicate using chemical cues, says Spencer. 鈥淎n egg is actually breathing. It鈥檚 sucking in oxygen and expiring carbon dioxide,鈥� he says. 鈥淚f you鈥檝e got a lot of well developed eggs in the nest, there would be more CO₂.鈥� This build up of CO₂ in the nest could trigger under-developed embryonic turtles to increase their metabolic rate.

Doing so makes sense from an evolutionary perspective, adds Spencer. Coordinating hatching times lets the vulnerable young turtles leave the nest in a group, making them less of a target for predators. 鈥淚f they don鈥檛 hatch out with their siblings, they鈥檒l be sitting ducks,鈥� he says.

Journal reference: , DOI: 10.1098/rspb.2011.2074