Previous studies have shown that various animals, from honeybees to chimpanzees, can learn to count when trained with food rewards. In 1998, researchers discovered that rhesus monkeys can not only learn to count to four, but can also pick up on numerical rules and apply them to numbers they haven't seen before, allowing them to count up to nine without further training.
With this finding in mind, psychologists at the University of Otago, in New Zealand, sought to find out if pigeons — another animal shown to count — have a numerical competence similar to rhesus monkeys.
" Pigeons are the perfect subjects for visual tasks, because their vision is really good and they're really easy to train," said psychologist Damian Scarf, first author of the new study. "It appears that you can train them on almost any task you can train monkeys on."
Scarf and his colleagues first trained three pigeons to count up to three. On a touchscreen, they presented the pigeons with a set of images that had objects of various sizes, shapes and colors. For example, one set presented images with one yellow block, two red cylinders or three yellow rectangles. To receive a treat, the pigeons had to select the images in the correct object-number order, from lowest to highest.
Once the birds learned to count to three, the researchers began showing the pigeons images with up to nine objects. On average, without higher-number training or food rewards, the pigeons were able to correctly order the image sets over 70 percent of the time. The pigeons had an easier time discriminating between lower numbers and numbers that were further apart.
"Once you start getting up towards seven, eight and nine, it was very difficult for (the pigeons) to tell the difference between the images," Scarf told LiveScience. Overall, the results of the study echoed those of the rhesus monkey research, though Scarf noted it took longer to train the pigeons than other researchers took training monkeys.
William Roberts, a University of Western Ontario psychologist who was not involved in the research, was surprised by the study's results. "I didn't anticipate that pigeons could have done that," said Roberts, who has previously researched animal cognition, including pigeon intelligence.
Roberts is curious to see how widespread this ability is in the animal kingdom. "Can we find evidence for this type of counting in insects, particularly bees?" he said. Finding the same level of numerical competence as the pigeons (and rhesus monkeys) in other species would help scientists understand if the ability evolved across species separately, or if a common ancestor shared the ability.
"We now have another piece of (the) puzzle," said Scarf, who is interested in performing similar experiments in parrots and other intelligent birds. "What's the origin of the ability?"