Goffin's cockatoos – or blushing cockatoos as they are also known because of the salmon-pink coloured feathers between their eyes and beak – are not only adorable, but also smart. A casual YouTube search will soon convince you of their shrewdness. And these blushing beauties are excellent problem solvers. They can make and use tools from different materials, such as sticks and cardboard, to extract food from boxes in the lab. Assessing the weight of objects is also a critical skill displayed by these wise creatures: gauging the mass of a nut may help them to infer its nutritional value or decide whether they are strong enough to carry it, and determining the weight of an object such as a stick, could help them to optimise how they use it as a tool. But can cockatoos tell the difference between objects that appear to be identical, but are of different weights? Poppy Lambert, Alexandra Stiegler and colleagues from the Messerli Research Institute and the University of Vienna, Austria decided to find out. They predicted that the cockatoos might be able to distinguish visually identical objects that differ in weight.

To test this, the researchers first let eight cockatoos use their beaks to pick up and assess the weight of purple and blue coloured spheres made of modelling clay wrapped around a fishing weight or a cotton ball and, when an experimenter instructed, they had to place each sphere in a transparent dish to receive a sunflower seed reward. Then the researchers trained them to distinguish between the clay spheres by picking up the heavier (or the lighter) of the two and placing it in a black dish, in return for a cashew nut reward and some verbal praise. After that, the team made the task more difficult, by making both spheres grey and thus visually identical. If the birds could genuinely tell the clay spheres apart by weight alone, then they wouldn't find it difficult to still pick out the heavier of the two grey spheres.

As the researchers predicted, the cockatoos correctly picked out the heavier of the two clay spheres with their beaks and placed them in a box that an experimenter presented, irrespective of whether the spheres differed in colour. If a cockatoo chose wrongly, the experimenter said, ‘nein’ (no) and the bird had to wait for 30 seconds before attempting another trial. Remarkably, the cockatoos could learn to differentiate objects based on weight after only 60 trials, faster than primates, which can take around 895 trials to learn a similar task. This is probably because birds need to be more sensitive to weight; flight is an energy-demanding task and so the animals need to be sure whether they have enough power to take off with a heavy burden.

Thanks to Lambert, Stiegler and colleagues, cockatoos now join the ranks of animals, including monkeys and chimpanzees, that can learn to discriminate quickly between visually identical objects based on weight alone; and they do so despite their dramatically different lifestyles. The research highlights that the phrase ‘birdbrained’ is not as insulting as some people might think.

Lambert
,
P. J.
,
Stiegler
,
A.
,
Rössler
,
T.
,
Lambert
,
M. L.
and
Auersperg
,
A. M. I.
(
2021
).
Goffin's cockatoos discriminate objects based on weight alone
.
Biol. Lett.
17
,
20210250
.