Many animals participate in contests and the winners of these contests often benefit from increased access to resources such as food and mates. For the red junglefowl, the ancestor of the domestic chicken, winning a contest can mean gaining a higher position in the social hierarchy or ‘pecking order’ of their group. But what determines who wins and who loses? This is a topic that researchers have been investigating for many decades.
Size matters, but what else?
“Morphology, for example how large you are, clearly plays a role”, says Hanne Løvlie, Associate Professor at the Department of Physics, Chemistry and Biology (IFM), Biology division, who led the project. “But, when contests take place between individuals that are similar in morphology, other factors may come into play. Individual differences in behaviour, such as personality and cognition, are found across the animal kingdom, but the consequences of these are still poorly studied. Therefore, we decided to investigate whether these differences could affect who wins and who loses contests.”
There are many traits of behaviour to observe, so the researchers had to make a decison on which ones to focus. “In many species, including red junglefowl, the individual that Laura Garnham, PhD student Photo credit Lejla Kronbäckinitiates the contest often ends up winning it. We, therefore, decided to focus on traits that could affect whether or not individuals initiate contests”, explains Laura Garnham, a PhD student in Biology division at IFM, working in Hanne Løvlie’s group, and first author of the study.
Based on this, the researchers chose to investigate multiple traits, including boldness, activity, aggression, impulsivity and optimism. They predicted that birds with higher levels of these traits would be more likely to initiate, and therefore, win a contest. “For example, bolder individuals may be more willing to take the risks involved in a contest, impulsive individuals may not stop to consider the possible negative consequences of initiation, and more optimistic individuals may initiate because they overestimate their chance of winning”, Laura explains.
The birds took part in a series of behavioural and cognitive tests to determine their individual levels of the chosen traits. Following this, they each took part in a contest with another bird that was similar to them in terms of morphology. “We did this to prevent morphology affecting the outcome of the contest”, Hanne says.
“Contests like this are a natural behaviour for junglefowl, and in most cases a winner emerges without much fighting. As more submissive birds will tend to avoid the more dominant ones, we considered a bird to have won the contest once its opponent had avoided its approach three consecutive times”, says Laura.
The researchers confirmed that contest initiators were indeed more likely to win. Males lived up to the prediction that bolder individuals would be more likely to initiate while females lived up to the prediction that more aggressive individuals would be more likely to initiate. However, the researchers also had some unexpected results, including that female initiators were less optimistic.
“It could be that less optimistic birds assume they will lose the contest. This could make them initiate to try to gain the upper hand, and put more effort into winning if they feel a contest is inevitable, resulting in them actually winning”, suggests Laura, “so it seems, at least in some situations, it may pay to be pessimistic.”
Further study on female contests needed
Overall, these findings bring us closer to understanding, not only what makes certain individuals more likely to win contests, but also the possible consequences of individual differences in personality and cognition. Additionally, that the behavioural traits that predicted contest outcome differed between males and females suggests that the sexes may establish hierarchies in different ways. “Most research on contests has focused on males, we therefore need more research on females”, Hanne points out.
The study was carried out solely at Linköping University. Funding was provided by Formas.
The role of personality, cognition, and affective state in same-sex contests in the red junglefowl
Garnham, L.C., Porthén, S.A., Child, S. et al. Behav Ecol Sociobiol (2019) 73: 149. https://doi.org/10.1007/s00265-019-2762-0