When Australian river turtles lay their eggs in a hole in a sandy riverbank, there is no good reason that they would hatch at the same time. You would expect them to hatch at different times as the eggs at the cooler base of the nest develop slower and should hatch later than the warmer ones at the top, but yet all of the eggs seem to hatch together.
To confirm that this is actually the case and to hopefully find out why, a recent study took eggs from the same group and put half at a low and half at a high temperature for two-thirds of the incubation period. The eggs were brought together for the final third period and what happened was interesting. The cooler eggs had caught up with the warmer ones and all of the eggs hatched together. But why?
Ricky-John Spencer at the University of Western Sydney, Australia says, “An egg is actually breathing. It’s sucking in oxygen and expiring carbon dioxide,” He explains, “If you’ve got a lot of well-developed eggs in the nest, there would be more CO2.” It is believed that the buildup of CO2 in the nest could trigger under-developed embryonic turtles to increase their metabolic rate, thereby playing catch up to join the others. It does make sense. Coordinating hatching times lets the turtles leave the nest in a group. This makes them less of a target for predators and insures that more can survive.