Big brains do not just develop overnight. To get that density of circuitry and higher order processing takes time. According to the "cognitive buffer hypothesis," this supposed "cost" of time spent in extended development is offset by the advantages afforded by larger brainsnamely, the ability to tailor behavior to different environmental stimuli.
A new study of birds provides the first physical evidence of this hypothesis. The report, published in the latest Proceedings of the Royal Society B, reveals that birds with bigger brains relative to their body sizes were found to have a better chance of survival in nature.
"Almost all studies in the past have only shown correlations between certain lifestyles and large brains," says study co-author Louis Lefebvre, a biologist at McGill University in Montreal. It took data collected by Lefebvre and Daniel Sol, an ecologist at the Autonomous University of Barcelona in Spain, along with another set of findings from biologist Tamas Szekely, of the University of Bath, and limnologist Andras Liker of Hungary's Pannon University to determine that a larger brain provides a survival edge. Lefebvre says that birds are ideal subjects, because so much is known about them. For example, scientists know the average brain size of nearly 2,000 species of birds. "They're easy to see and people enjoy watching them," he notes. "Many mammals are nocturnal or they have camouflage colors and they're not particularly interested in being watched. But with birds, you can gather enormous amounts of information."
Sol and Lefebvre had previously collected data on relative brain sizes for several species of birds. Meanwhile, Szekely and Liker had surveyed roughly 220 avian species from polar, temperate and tropical areas; they studied mortality rates using such methods as capture-and-release, putting little bands on a sampling of birds during the warm months and keeping tabs on how many returned after the cold season.
When the two teams merged their independent findings (and corrected for factors such as migratory behavior, protracted care by parent birds, style of chick development and competition for reproductive success), they found that there was significant correlation between adult brain size (relative to the body) and low mortality rates.
"What the cognitive buffer hypothesis assumes is that animals have some way of responding to a difficult situation," Lefebvre explains. "For instance, by being innovative--instead of starving to death when the food supply is low, finding food in a different way--those animals have an edge and that is the mechanism that leads to increased survival."
This ability to innovate is seen in birds such as the raven and hornbill, which are able to colonize and propagate in new regions and withstand seasonal weather disruptions; smaller brained ducks and emus, however, are less resilient. According to Szekely, the new findings "suggest that large-brained animals might be better prepared to cope with environmental challenges such as climate change and habitat destruction."
Lefebvre stresses that birds with relatively small brains (compared with the rest of their bodies) are not necessarily doomed. "Obviously there must be something that's keeping those small-brained birds around, because an advantage like that would normally lead to selection against any [genetic variants] that would lead to small brains in the species," he explains. Yet, partridges, pheasants, and even emus continue to thrive.