It's almost spring, and for many animals, warmer weather means it's time to find a mate. If you're a bird, finding that mate means a new clutch of eggs won't be far behind.
But keeping those eggs safe until they hatch can be a challenge, especially if you're a Japanese quail — a small ground-nesting bird that counts foxes among its predators.
The eggs of Coturnix japonica are tiny — not much bigger than a quarter. They're off-white or tan in color, with darker speckles.
But, it turns out, there's a lot of variation in the way the eggs are flecked. Karen Spencer, a behavioral ecologist at the University of St. Andrews in Scotland, noticed something particular. "We could tell which females were laying the eggs by the colors and the patterns on them," Spencer says. "You can actually discriminate ... as to which female is laying what egg."
One female, she says, will lay eggs with big dark splotches covering a lot of the shell surface. Another's eggs will have almost no spots at all.
The patterns intrigued Spencer and her colleague, George Lovell, a vision scientist at the universities of St. Andrews and Abertay. "We wondered whether the actual patterning helped to hide the eggs from predators," Lovell says.
And was it possible the quail were aware of the colors and patterns of their eggs, and actually choosing where to lay them based on how well they would blend in with their surroundings?
Spencer and Lovell designed an experiment to find out. First stop? The pet store, to buy some colored aquarium sand.
"We had black sand, a kind of orangey-brown sand, a yellowy sand and then a sort of whitey-cream, off-white sand," Spencer says.
They put the sand on trays, and put the trays — together with the quail — into large enclosures. Then they just let the quail do their thing for seven days and kept track of where the birds nested. Most of the time, Lovell says, the quail picked the sand that looked most like their eggs.
Birds with eggs that had very light spotting — less than about 30 percent spotted — tended to lay the eggs on off-white or yellow sand that matched the background color of the egg, Lovell says.
But quail with eggs that were darkly flecked — more black or brown spots — chose darker sand that tended to match the spots, not the background, he says. In the world of camouflage, that's known as "disruptive coloration."
"Essentially what it's doing [is] it's trying to hide [the egg's] outline," Lovell says. "You'll see [that same strategy] in military camouflage, and you'll see it in insects and things like that as well."
"It's a very clever study," says Martin Stevens, an evolutionary biologist at the University of Exeter in England who wasn't involved in the quail research. This may be the first study, he says, to show that animals are able to actively seek out surroundings that enhance their ability to camouflage themselves — or their offspring.
"The more concealed they are, the less likely they are to be detected and eaten by a predator," Stevens says. "So it could be a very big survival advantage."
He predicts that scientists who look will find examples of this camouflage-enhancing behavior in other ground-nesting birds — and maybe in other animals, too.