When faced with more than one alternative, the simplest response would be to choose randomly. A more challenging strategy would require an analytical interpretation based on previous experience. One way to do this is to infer by exclusion: choose one option by logically excluding the others. Until recently, we thought the ability to infer by exclusion was a uniquely human trait, but several studies in the last decade have shown that that’s simply not the case. 

University of Vienna's Mark O'Hara and colleagues wanted to see if highly curious Goffin cockatoos (Cacatua goffini) act according to the exclusion principle. These Indonesian birds have already shown remarkable cognitive capacities, and they have a tendency to explore new and novel items. Called neophilia, that proclivity is believed to have evolved in island species, which tend to be threatened by fewer or no predators. 

First, a dozen Goffins were trained to associate a picture with a food reward that would automatically be delivered in a tray after they touched the image on the touchscreen (pictured). Touching the picture next to it resulted in no reward. However, sometimes the unrewarded stimulus was occasionally replaced by something novel. After the birds had started to reliably pick the positive stimulus over the novel (and negative) ones, that meant they were ready for the inference test. This helped make sure the birds didn’t pick novel pictures simply out of curiosity. 

Then in the tests, the birds were presented with various combinations of novel and familiar images that could be rewarded or not. "More than half of our cockatoos choose their pictures in a way that clearly indicates the ability to infer by exclusion," O'Hara said in a statement. Their findings were published in PLoS ONE earlier this month. 

Goffin cockatoos now join humans, non-human primates, dogs, goats, ravens, crows, and African grey parrots with their ability to infer by exclusion. Not in this group: pigeons and sheep. 

Image in text: Mark O'Hara