Birds eavesdrop on chipmunks to protect their young, suggests a new study.
Veeries and ovenbirds are small, ground-dwelling birds that are relatively rare sights around St. Albert, says local birder Peter Demulder. (You’d have better luck finding them in Elk Island National Park.) Both nest on or near the ground, putting their eggs at risk of predation by squirrels and chipmunks and both have distinct calls: “VEE-ree VEE-ree” for the veery and “tea-CHER tea-CHER” for the ovenbird. The ovenbird’s nest is notable for its shape, which resembles a Dutch oven.
Quinn Emmering, a biologist at Texas Tech University, says he and his team had noticed veeries had a knack for finding “cold-spots” for predators like chipmunks in which to build their nests, and were more successful at reproducing when they did. He theorized the birds were listening for chipmunk calls to find where best to put their nests.
Emmering and his team went to an oak forest in Millbrook, N.Y. and set up 40 experimental plots. They placed speakers or flags in the middle of each that broadcasted, at random intervals, the sounds of deadly chipmunks, harmless frogs or (in the case of the flags) silence. They then spent two years tracking how far veeries and ovenbirds built their nests from these sound sources.
Emmering says his team found that both birds nested much further away from plots playing chipmunk calls than those playing frog calls or silence. Notably, the ovenbirds’ response was twice that of the veeries’: they nested about 20 metres farther from the chipmunk sounds compared to the frog and silent ones, while the veeries nested just 10 metres further. Bird counts also found fewer ground birds than canopy birds at chipmunk sites, suggesting they might be avoiding these regions altogether.
This appears to be the first study that shows nesting birds eavesdropping on the calls of predatory mammals, Emmering says. It also suggests that ovenbirds are more attuned to chipmunk calls than veeries, which could give them an advantage when chipmunk numbers rise. Ovenbirds have had three times the reproductive success of veeries at the test site this year, which could be due to the site’s spike in chipmunk numbers.
These results make a lot of sense, says Demulder, and probably apply to squirrels too. “Squirrels are deadly when it comes to nesting birds.”
The study can be found in this week’s Journal of Animal Ecology.
Researchers came closer to cracking the mystery of sleep this week thanks to some glowing fly brains.
Chiara Cirelli, a neuroscientist with the Wisconsin Centre for Sleep and Consciousness, co-authored a paper on fruit flies and sleep in this week’s issue of Science.
Everyone knows sleep is important, Cirelli says, since you feel really bad when you don’t get any of it, but no one is sure why.
One theory is that it has something to do with our synapses. Synapses are connections between neurons that transmit signals in our brains. The brain builds up these connections while we’re awake and learning. That’s great, Cirelli says, but these connections take up a lot of space and power — eventually we max out and can’t learn any more. Cirelli’s team theorized that sleep trimmed back these connections to save energy, leaving only the strongest, most important memories behind.
To test this, her team took a few hundred fruit flies and put them in one of two environments: boring isolation tubes where they couldn’t fly or interact with each other and a bigger “fly-mall” bottle where they could zip around at will. The flies were modified to make some of their neurons glow green, red or yellow. The flies went back into the tubes after 12 hours in the mall. Some slept for seven hours, while others were kept awake by shaking the tubes.
The team removed the flies’ pen-tip sized brains and examined them under a microscope. They found the flies in the mall had more synaptic connections than ones kept in the tubes, and that the extra connections mostly disappeared after a seven-hour nap. Mall visitors that were denied rest kept their high number of connections. They also found that flies that went to the mall slept more than those that stayed in the tubes.
This strongly suggests that animals sleep to trim their synapses back to reasonable levels, Cirelli says — how sleep does this is still unknown. “Don’t forget to sleep if you want to remember stuff,” she concludes.
