Giving pigeons in the park bread could be making them more aggressive, according to a new study that found heavier birds were the most dominant.
A team from the University of London examined dominance in pigeon society and looked at which had better access to resources such as food and mates.
They found that heavy birds dominated in pigeon groups and if a light bird was ‘fattened up’ it would be quickly climb the ranks and become dominant.
‘It’s possible the added mass made them feel in better physiological condition, and more willing, therefore, to pick a fight,’ according to the research team.
Giving pigeons in the park bread could be making them more aggressive, according to a new study that found heavier birds were the most dominant
Many animals live and travel in groups, giving them enhanced vigilance and predator detection – but individual personality characteristics can lead to conflict.
This leads to some individuals within a group coming out as dominance and this has been seen throughout the animal kingdom, the team explained.
There are benefits to this ‘dominance hierarchy’ within a group – the team say it reduced the severity and incidence of physical conflicts with other groups.
By reducing the time devoted to these encounters, time can be invested in other important behaviours such as maintenance, vigilance and foraging.
Previous studies have linked linear hierarchies – that is an order of dominance – to parameters such as body mass and size.
The order is stable or unstable and varies over time and the researchers from London found that in pigeons size really does matter.
The bigger the bird the more aggressive they are likely to be and the most aggressive birds tend to become the most dominant within a group.
To determine this was the case the team studied 17 homing pigeons held at the Royal Veterinary College in Hatfield, Hertfordshire – eight males and nine females.
They were all six years old and had been held since they were a year old – they were given regular access to food and awater and no other birds were added to the group.
Birds were studied at three points in their annual cycle over three years and after 19 months the nine birds at the bottom of the pecking order were made heavier.
The team added artificial weights to the backs of the birds – who were used to having artificial objects applied to their bodies.
Before the extra weights were added the dominance hierarchy among the birds was stable, but this changed dramatically at the next measuring session.
Those with ‘extra mass’ became noticeably more dominant and became more aggressive – increasing their rank in the group.
It was the male birds that became the most aggressive when they ‘got bigger’ with one becoming up to 750 per cent more aggressive, according to researchers.
The experiment actually led to an overall increase in the aggressiveness of the flock and in the number of aggressive encounters.
They found that heavy birds dominated in pigeon groups and if a light bird was ‘fattened up’ it would be quickly climb the ranks and become dominant
When the ‘extra weights’ were removed from the birds the original hierarchy – from before the experiment – returned and the previously weighted birds stepped back into line – suggesting no carry-over or memory of the effects.
‘There is no clear pattern yet determined as to why body mass is such a strong determinant of dominance in some species but not others,’ the authors explained.
‘It is possible that body mass is a significantly correlated with dominance in species where secondary-sexual ornamentations are less pronounced, and as a result, signalling is less clear.
‘In such cases, body mass may become more of an important indicator of fitness.’
The study shows that aggressive traits can be modified and increased by ‘feeding up’ birds – so pigeons who compete for breadcrumbs in cities could be more aggressive as a result of humans leaving food out for them.
The findings have been published in the journal Biology Letters.
