# Hummingbirds were able to understand the concept of number order

Scientists have noticed that hummingbirds can memorize sequences of numbers and, based on them, build a strategy for obtaining food. They believe that this is the first time a wild animal has performed simple mathematical operations.

Humans are the only creatures capable of performing complex mathematical operations. However, some animals understand what counting and sequencing are. A group of researchers from the University of St Andrews in the UK and the University of Lethbridge in Canada have found that hummingbirds understand some of the properties of numbers and can use them to find food. In an article published in the journal Proceedings of the Royal Society B, they describe the experiments they conducted with birds and what they learned from them.

The experiments took place in the Rocky Mountains in North America, where ocher hummingbirds (Selasphorus rufus) live. The team built artificial flower feeders for them and allowed the birds to fly to them for a while so that they got used to this diet. The researchers then caught several hummingbirds, for which an array of four rows of ten feeders was designed. In each row, only one was filled with sucrose solution, the rest were empty.

On each visit to the array, the birds examined the flowers until they found a single one with nectar. Scientists recorded the order in which they flew up to the feeders, and then moved them so that hummingbirds could not visually remember the location of the flower with nectar. Only the row of feeders and the distance between them changed, but not the order.

a) photograph of the data set. b) red-headed hummingbird touching an artificial flower. / © Tom Oldridge. c) a schematic representation of the possible positions of the training arrays. d) training array (top) and sample test array (bottom). Outlined flowers are boosted positions (no test reward). / © Proceedings of the Royal Society B: Biological Sciences (2020).

During experiments, hummingbirds unmistakably found a full feeder, regardless of where it was located. It turned out that the accuracy of their calculations is almost independent of the ordinal number of the flower with nectar: in the overwhelming majority of cases, they found the correct one. This may indicate that the birds understood what number the food was under, and performed simple mathematical operations, for example, ordinal counting.

The distribution of errors was not constant. When the first trough was full, hummingbirds flew around the rest less often than when it was placed in fourth position. Moreover, if the birds were mistaken, then they chose a flower that was closer to the beginning of the row. "This could be the result of errors caused by generalizing the spatial arrangement of the flower with the reward: the bird remembered that the reward was near the nearest edge of the array," the authors of the article say.

They believe their study represents the first demonstration of number sequence memorization in free-living wild vertebrates, and will continue testing to see if hummingbird skills reflect their role as pollinating birds.