As you might guess, big-brained birds survive better in the wild than those less cerebral for their size. Scientists guessed that too, but they had to prove it to themselves.
“The supposition that large brains are associated with reduced death rates has not been tested in any group of animals,” notes Tamás Székely, a visiting fellow at Harvard’s Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology.
Big brains have their disadvantages, biologists admit. They exact a high cost from their owners in the form of development time and upkeep demands. Evolution would eliminate them if they did not provide benefits to offset that cost. The benefit is obvious when you see a large-brained red-tail hawk capture a small-brained pigeon for its lunch.
However, big brains, in this case, refer not just to large brains in large animals, but to brains that are large relative to body size. According to Louis Lefebvre of McGill University in Montreal, some cockatoos with a body weight of one pound carry brains that weigh about half an ounce. Contrast this to partridgelike willow ptarmigans or spruce grouse that weigh about the same as cockatoos but have brains that weigh around a tenth of an ounce, or three to four times smaller than that of a cockatoo.
If what zoologists believe is true, cockatoos should survive better than these ptarmigans or grouse. Székely and Lefebvre, along with Daniel Sol, an ecologist in Spain, and András Liker, a limnologist in Hungary, set out to determine if that’s actually what happens.
Survival of the brainiest
The investigators gathered information on the brain size, body mass, and death rates of 224 species of birds that live in polar, temperate, and tropical locations. The results “clearly demonstrate that larger brains, relative to size, are associated with higher survival in nature,” notes Székely.
Cockatoos have yearly death rates between 6 and 12 percent while the willow ptarmigan is in the 35 percent range. In other words, their rate of death is about three to six times greater than the brainier cockatoos. For the spruce grouse, survival is even more difficult with an annual death rate of 50 percent. Fully half of any population of spruce grouse dies in an average year compared with only about 10 percent of cockatoos.
The research results will be published in an upcoming issue of the Proceedings of the Royal Society. The information is now available at http://www.journals.royalsoc.ac.uk.
Obviously, the smarter a species, the better able it is to survive a food crisis, say, by finding other sources of nourishment. A bigger brain also aids in dodging predators. Yet, it’s not just survival of the fittest that counts in the big picture of evolution. “It’s reproductive success,” Lefebvre notes, “surviving long enough to make more copies of yourself. Studies in England show that populations of small-brained birds are declining faster than their big-brained relatives.”
However, the researchers caution, they have not found unambiguous proof that birds change their behavior in response to challenges of climate change, food shortages, or loss of shelter. “If the connection is confirmed,” Lefebvre says, “it would provide a new perspective to understanding why the brain has evolved so fast in porpoises, apes, and humans, as well as in ravens and parrots.”
If bigger brains do drive flexibility and change, it could forecast how well various animals will survive the challenges of global warming. What might cockatoos do that ptarmigan and grouse never “think” of? What will humans do that a monkey like a maroset cannot, and how will all that affect evolution?