By Ella Davies
Earth News reporter
Bucks that butt-in get the girls
Male fallow deer intervene in fights between rivals to assert their dominance, according to scientists.
Studying the bucks during the mating season, researchers say they found the first evidence of strategic behaviour in deer.
By interrupting fights, males are able to display their dominance whilst subduing multiple competitors.
These fights happen annually during the autumn mating season or "rut" when males compete for access to females.
Researchers from Newcastle University, UK, University College Dublin, National University of Ireland, Galway and the Galway-Mayo Institute of Technology, Ireland made the new observations.
They studied a herd of over 500 fallow deer in Dublin's Phoenix Park to learn more about behaviour during the rut.
Their findings are published in the journal Animal Behaviour.
Fallow deer form sexually segregated herds for most of the year but "batchelor herds" of males move onto female ranges from the beginning of September.
During the rut, bucks are known to engage in fierce combat in order to prove their dominance and gain access to females.
The rut is a noisy time when males "groan" to call out rivals
Competing males strut shoulder to shoulder to size each other up
Males fight using their powerful antlers that regrow every year
Competitions can be "to the death" via injury or sheer exhaustion
Previous studies have highlighted how age, body size and antler size are important qualities that determine which buck will be triumphant.
However, research by Dr Domhnall Jennings and his team identified an added layer of complexity to the male deers' behaviour.
Scientists observed individual bucks intervening in fights between two other rivals, but Dr Jennings explained, the deer were not acting as peacekeepers.
"Diplomatic explanations have been used for intervention behaviour in primates as a means of enhancing group stability and cohesion," he told the BBC.
"This is not the case here since the bachelor herd has dispersed and males are extremely intolerant of each other's presence during the rut."
Rather than trying to maintain harmony in the group, researchers found that the fallow bucks strategically interrupted fights to improve their own status.
"There can really only be a despotic explanation for this behaviour in deer; [intervening males] benefit directly from their behaviour whereas the originally competing males do not," said Dr Jennings.
After interrupting the fight, dominant males then went on to defeat one rival whilst ignoring the other, leaving the original contest unresolved.
"As a result of having their fight interrupted in this manner, the original competing pair of males retain their status quo... the time and energy they have spent on fighting is wasted while their ability to advance in the hierarchy and mate is also impaired," said Dr Jennings.
Researchers say this work represents the first evidence of strategic behaviour in deer.