Newcastle University

Observing behaviour during rutting season, scientists have noted how a male deer will often intervene in fights between two other rival males and go on to attack one of the fighting males. By disrupting fights in this way the buck benefits as his status improves and he gains more mating opportunities.

This study shows for the first time that deer are capable of strategic behaviour as intervening in a fight can provide a buck with a significant advantage over rivals.

Researchers from Newcastle University, UK, University College Dublin, National University of Ireland, Galway and the Galway-Mayo Institute of Technology, Ireland, spent two years studying a herd of over 500 European fallow deer in Dublin.

In nature, it is common for males to aggressively compete with each other in order to obtain access to receptive (oestrus) females. However, fighting between males over females can be costly to the combatants in terms of the amount of energy expended and the risk of suffering a disabling injury so the rewards must outweigh the risks. In a fight between two bucks, intrinsic qualities such as size, age and the size of antlers determine who is going to win – or dominate opponents.

However, this study shows that it is not just straight fights which can improve a buck’s status - disrupting a fight can also lead to more success with females.  The researchers observed that this intervention behaviour yields significant benefits for the intervener: they benefit from an increase in dominance status and achieve a substantial increase in mating success.

It is the first evidence that animals engage strategically in third-party intervention behaviour – disrupting fights to improve their status to gain more mating opportunities. Researchers observed that bucks who intervened in fights went on to dominate the combatants and as a consequence had increased success in mating.

Dr Domhnall Jennings, Lecturer in the Institute of Neuroscience at Newcastle University who led the research said: “Intervening in fights affects the status of all those involved. Not only does it increase the dominance of the intervening buck but as a result of having their fight interrupted in this manner, the original competing pair of males retain their status quo; therefore, the time and energy they have spent on fighting is wasted while their ability to advance in the hierarchy and mate is also impaired.”

Reference: Third-party intervention behaviour during fallow deer fights: the role of dominance, age, fighting and body size, Dómhnall J. Jennings, Caitríona M. Carlin, Thomas J. Hayden and Martin P. Gammell. Animal Behaviour.

Photo: Fallow deer bucks strut shoulder to shoulder to size each other up
Credit: William Clarke, University College Dublin

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