That people have personalities goes without saying. There are the shy, the cruel, the kind, the sceptical. Pet owners will quickly argue that their animals have personalities too. It is hardly uncommon to hear a dog described as friendly or inquisitive, and scientific research has confirmed that dogs do indeed have personality traits similar to those found in people. In dogs, for instance, these are usually referred to as energy-level, affection-aggression, anxiety-calmness and intelligence-stupidity; in people they are extroversion, agreeableness, neuroticism, openness to experience and conscientiousness.

Yet in spite of all this, rather little has been done to find out if such characteristics exist in wild animals. One such study, published recently in Animal Behaviour, shows not only that some do, but also that the presence of such traits is skewing the way data are collected by researchers.

The animals in question are birds — collared flycatchers, to be specific. László Garamszegi, who was at the University of Antwerp at the time of the study (he is now at Doñana Biological Station in Spain), and a team of his colleagues monitored the courtship behaviour of this species. The 41 males observed were nesting in boxes long used by the species, and a single attractive female was placed in an enclosure on top of each box.

First, the team measured the varying intensity of the courtship behaviours displayed by the 33 males that responded to the caged female. After they had collected enough data to act as a baseline, they then attached a white piece of paper to each of the boxes used by these males and watched how the males in question responded to this novelty. They found that roughly half seemed afraid of the paper and reduced their courtship of the female. The other half ignored the paper and continued displaying as they had done before.

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