Many birds use tools for diverse reasons, such as extracting and capturing food. It may look cognitively sophisticated, but some of this tool-use behavior is stereotyped, built into the species' genetic inheritance. An example of this is 'anting' — some birds rub live ants on their feathers, apparently to spread the insects' formic acid over their bodies as an antibacterial or insecticide. There is no indication that the birds are engaging in this behavior, in which case the ants are the tools, intentionally or with a conscious understanding of what they are doing.

However, there are also more cognitively flexible examples of tool use, which could indicate more complex underlying thinking. Scientists recently described the use of tools in birds called great antshrikes. The birds were observed using stone anvils to break open the shells of land snails. The behavior is almost certainly of recent origin, as there were no previous reports of these birds using tools and the land snail was introduced to the birds' habitat very recently, in the 1980s.

Giant Land Snail. Jeremè, via Wikimedia Commons.

In northern Brazil, Richard Ladle and colleagues observed a male great antshrike catching juvenile land snails, bringing them repeatedly to the same oval-shaped stone, and breaking their shells by striking them against the anvil. They watched this same bird engage in this behavior four times over several days.

The researchers found evidence that the tool-use was not limited to the one male. They discovered two other large piles of broken shells, both next to hard objects that could serve as anvils. Ladle also says that the antshrikes make a loud "thock thock thock" noise as they batter the snails against the stone, and the team often heard snails being smashed simultaneously.

Ladle and his colleagues say it is very likely that this is an example of flexible tool use. The land snails were accidentally introduced to Brazil in the 1980s, and there are no reports of great antshrikes using tools previous to this.

Antshrikes are clever birds that feed on a wide variety of animals from seeds and invertebrates to lizards and even small mammals. "They are quite opportunistic, being found in a variety of 'new' habitats such as plantations and gardens," says Ladle. "All this suggests that they are, cognitively speaking, flexible and able to modify their behavior relatively quickly in response to changing environmental conditions."

The researchers suspect the tool-use behavior developed as a result of the high density of snails in this particular habitat and a bit of luck, such as one bird learning how to crack the snails and the innovation spreading through the population. Ladle says a similar thing happened when blue tits learned how to peel open the foil tops of milk bottles in the early 20th century in England. The behavior emerged due to a combination of the right environmental conditions (milk bottles left on people's door steps) and an adaptive behavior spreading among a population.

The behaviors of many South American bird species are not that well-known. This study suggests that cognitively sophisticated and flexible behaviors may be more common in birds than previously thought. It might just take the right environmental conditions, and a little innovation, to get a population to learn how to use new tools.

Reference:

Efe, M. A., de Paiva, F. N., Holderbaum, J. M., and Ladle, R. J. (2014). Rapid development of tool use as a strategy to predate invasive land snails. Journal of Ethology. doi: 10.1007/s10164-014-0412-6.