In the third phase of the experiment a male was placed in the cage over the box where the female had once been, and the amount of aggression towards this male from the nesting male was measured. In general, those males who had been undeterred by the presence of the paper attacked the newly presented competitor with vigour while those who had been intimidated by it seemed reluctant to attack the putative competitor if, indeed, they attacked him at all.

Another part of the study analysed male willingness to fight in the presence of potential predators, by watching aggressive interactions between nesting males and caged competitors when an unfamiliar human slowly approached the site. Those males who had been afraid of the paper often fled when the human was as much as 20 metres away. Those who had continued their courtship in the presence of the paper again proved their courage and often kept fighting until the observing human was just two metres away.

Lastly Dr Garamszegi and his team placed traps within the nesting boxes and monitored which birds were caught. They found that the aggressive, risk-taking males were twice as likely as non-risk-takers to be trapped.

These results are both interesting and worrying. They are interesting because this is the first time that differences in personality have been shown in wild birds. If birds, as well as mammals, have personalities, it may make it easier to study the evolutionary pressures that give rise to such systematically different ways of behaving within a single species.

... contd.