The ability to make inferences based on statistical information has so far been tested only in animals having large brains in relation to their body size, like primates and parrots. In a new study at Barcelona Zoo, researchers tested if giraffes (Giraffa camelopardalis), despite having a smaller relative brain size, can rely on relative frequencies to predict sampling outcomes.
Giraffes can calculate which option is more likely to produce their preferred food based on basic statistical calculations. Image credit: Howard Wilks.
The ability to make statistical inferences is considered a highly developed cognitive function and has only been tested in large-brained animals such as primates and keas (Nestor notabilis).
However, the statistical abilities of animals with proportionally smaller brains, such as giraffes, have not been tested.
In a new study, Dr. Federica Amici, a researcher at the University of Leipzig and the Max Planck Institute for Evolutionary Anthropology, and her colleagues presented two male and two female giraffes at Barcelona Zoo with a choice between two vegetable sticks held in a closed fist that had been drawn from transparent containers holding different proportions of preferred carrot sticks and less-preferred courgette (zucchini) sticks.
While the giraffes could see the amounts of the different vegetables in each container, they could not see which vegetable the authors selected and offered.
The different conditions included a container holding 20 carrots plus 100 courgette pieces versus one holding 100 carrots plus 20 courgette pieces, 20 carrots plus 100 courgette pieces versus 20 carrots plus four courgette pieces, and finally 57 carrots plus 63 courgette pieces versus 3 carrots and 63 courgette pieces.
The latter two conditions tested whether giraffes could assess the relative frequencies of the vegetables, rather than just the absolute numbers of each.
In at least 17 out of 20 trials, the giraffes were reliably able to select the container that was more likely to produce their favoured carrot sticks.
The researchers used control conditions to rule out whether the giraffe were using any other information, such as their sense of smell (instead of seeing the containers) or clues from the experimenters, when making their choice.
These results demonstrate statistical reasoning akin to that observed in primates and keas.
Given the relatively small brain sizes of giraffes, the scientists suggest that a large brain may not be a prerequisite for complex statistical skills, and that the ability to make statistical inferences may be more widespread in the animal kingdom than previously thought.
“In evolutionary terms, statistical abilities might provide crucial fitness benefits to individuals when making inferences in a situation of uncertainty, and it should, therefore, not be surprising if these abilities are widespread across animal species,” they said.
“In the future, it would be interesting to test more species with these experimental procedures, and use a comparative approach to assess whether the specific socio-ecological challenges faced by different species reliably predict the distribution of statistical skills across animals.”
“Very likely, statistical skills may be present in several other species.”
The findings appear in the journal Scientific Reports.
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A.L. Caicoya et al. 2023. Giraffes make decisions based on statistical information. Sci Rep 13, 5558; doi: 10.1038/s41598-023-32615-3
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