Turtle embryos seek warmth

Cold-blooded creatures spend their lives moving around their environments, on a Goldilocks-like hunt for the perfect temperature. But what happens when you live inside an egg?

Scientists had previously observed the embryos of soft-shelled turtles moving toward warm spots inside their eggs, but they couldn't tell whether the movement was intentional or passive, driven by a trick of fluid dynamics.

So a team of researchers decided to experiment. They incubated 125 Chinese three- keeled pond turtle ( Chinemys reevesii) eggs at various temperatures, creating spots in the eggs that were too hot, too cold, and just right.

Live embryos consistently moved toward warm spots but retreated from the dangerous hot spots, the researchers reported online Tuesday in Biology Letters.

Meanwhile, dead embryos didn't move at all, indicating some intentionality at work in their living kin.

Because subtle differences in incubation temperature determine C. reevesii's sex, it's possible that the embryos themselves have some control over whether they are born male or female.

- Lizzie Wade

Wrens learn to drive off cuckoos

When cuckoos start hanging around the nests of superb fairy-wrens ( Malurus cyaneus), pint-sized songbirds in Australia, the wrens need to act quickly. Otherwise, the cuckoo will lay eggs in their nests, giving rise to chicks, which the wrens tend, even as the interlopers push the wrens' own offspring out.

But how are wrens that have never seen a cuckoo before able to recognize the threat? According to a study published Tuesday in Biology Letters, they rely on their more knowledgeable family members.

Researchers identified both naive and " cuckoo- experienced" individuals in family groups and placed a freeze-dried specimen of a shining-bronze cuckoo inside a camouflaged cage 2 meters away from a nest.

When a naive fairy-wren was alone near the nest, the scientists drew back the camouflage with a hidden chord and exposed the perched cuckoo.

Not one of the 11 naive birds that they tested made so much as a peep when they saw the cuckoo.

But after the newbies watched experienced birds respond to the cuckoo model, mobbing it and shouting alarm calls, they joined in the attack.

It took only one exposure to the actions of the more knowledgeable birds for the innocent ones to change their behavior, the scientists report.

This kind of speedy social learning typically occurs, they note, when you can count on others of your kind to give reliable signals, and when the cost of learning something on your own is exorbitant - which is surely the case for any cuckoo- parasitized songbird.

- Virginia Morell