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Kea: Less dominant behaviour brings about the desired success

16.03.2021: Kea (Nestor notabilis) are an endangered species of large parrot from New Zealand that are known for their intelligence and curiosity, making them an interesting species for behavioural research. A recently published study conducted by researchers from Vetmeduni and international partner institutions shows that dominant behaviour in kea is an obstacle to successful cooperation. When higher-ranking birds learned to restrain themselves, however, their success increased.

Working with a group of captive kea, an international research team led by Vetmeduni Vienna investigated which factors help or hinder cooperation among multiple animals when they are free to interact with each other. “We anticipated tolerance by dominant animals to be a major factor potentially impeding cooperation. We expected to see more tolerance, and hence more successful cooperation, among animals with stronger affiliative bonds and with smaller rank distances,” says first author Raoul Schwing from the Messerli Research Institute of the Department of Interdisciplinary Life Sciences at Vetmeduni, explaining the basic hypothesis of the study.

The best way to get the reward

The researchers tested the influence of dominance, rank distance, tolerance, affiliation and coordination on cooperation using a wooden box requiring two, three or four chains to be pulled at the same time to access a food reward. The reward could be divided unevenly, but not monopolized completely by one animal. “We started by familiarizing the animals with the apparatus individually by allowing them to pull a single chain that opened the lock holding the bottom of a wooden box. This allowed access to a food reward. By adding a second chain at the opposite side of the box, we created a dyadic cooperation task in which two subjects had to pull two chains simultaneously to obtain the reward,” says Schwing.

Less dominant behaviour allows for cooperative success

At the beginning of the experiments, however, the dominant animals were so keen on defending the closed wooden box that none of them showed enough restraint to allow any lower-ranking kea present to pull either of the two chains. The researchers therefore adapted the experimental set-up by now confronting all 16 kea participating in the experiment with the wooden box with two chains attached. During this “group session”, two birds managed to pull on the chains at the same time. After several trials involving all of the birds, the box was finally opened. After this session, the dominant birds allowed lower-ranking individuals to handle the chains.

The researchers were then able to carry out their tests as originally planned. They added a third and finally a fourth chain to study the cooperation between three and four animals. In these tests, restraint by dominant birds remained the strongest factor determining success. It is interesting that kea can overcome their dominance and learn to adapt in the group. Schwing: “The probability of success increased with the degree of restraint shown by the dominant birds that were present. Previous experience with the task contributed to success in subsequent sessions, while increasing rank distance reduced success notably in the four-chain setup. While there are many factors that would still need further study to determine their effect on cooperation, we were able to show for the first time that four kea can work simultaneously on the same apparatus to gain access to a sharable reward.”

Important contribution to better understanding cooperation among groups of animals

A particular value of the study is that it tested the cooperation of several animals working simultaneously. According to the researchers, experiments in which more than two animals can obtain rewards by acting in a coordinated manner are rare. “This is surprising considering that many forms of cooperation in nature strongly depend on the behaviour of multiple individuals, for example in cooperative hunting by lions and other carnivores as well as chimpanzees in cooperative defence against predators,” says Schwing.


Kea during the experiment


The article “Kea, Nestor notabilis, achieve cooperation in dyads, triads, and tetrads when dominants show restraint” by Raoul Schwing, E. Meaux, A. Piseddu, L. Huber und R. Noë was published in Learning & Behavior.