Humans often choose partners based on behavioural keys that are displayed during social interactions. The way we behave in different social contexts can reflect personality traits or temperament that may inspire long-term love. Behavioural norms that we perceive as sexually attractive are not culturally or evolutionarily arbitrary.

However, personality-mediated sexual selection is not just the privilege of mankind. László Garamszegiand colleagues at the University of Antwerp and at Eötvös University, Budapest used bird song as a model to investigate whether behavioural traits involved in sexual advertisement can serve as good indicators of personality in wild animals.

Behavioural ecologists have begun to recognise the evolutionary importance of personality traits in many animal taxa, from fishes to high vertebrates. Birds are often used as a model in personality research, and past studies have demonstrated that individuals do display consistent behavioural responses on different days, and individuality can even be manifested across different ecological situations (aggression, for example, is expressed in a male-male context, while its correlated response, risk taking is at work in a predator-prey context).

Bird song has a prominent and well-established role in sexual selection, and it displays considerable variation among individuals, with a potentially strong personality component. For example, singing may reveal risk taking, because conspicuous songs attract not only the interest of females but also the attention of predators. Hence, only high-quality individuals can afford to display attractive songs, and these will necessarily be risk takers. Moreover, exploration may also be expressed in a bird's vocal repertoire, as adventurous individuals will explore a range of habitats where they encounter diverse acoustic features from other individuals that can be incorporated into their song.

Garamszegi and colleagues sought to determine the relationship between song and personality. The researchers recorded the song of 24 males in a European Collared Flycatcher population and characterised several song features. They also performed behavioural tests with the same males to determine explorative behaviour in an altered breeding environment and to assess risk taking when a potential predator was approaching. The main finding of the research was that males observed singing at low song posts relative to the surrounding vegetation were seen as explorers and risk takers in the corresponding personality tests.

Singing close to the ground may involve higher predation risk, because it offers less concealment and puts males in a conspicuous position from the predators' eye. Hence, only prime quality individuals can cope with such costs of exposed singing, while cheaters will be eliminated by predators. Apparently, the choice of song post can influence mating success, because males from lower posts were also found to establish pair bonds earlier, which is probably due to the female preference for males singing in exposed sites.

These results reveal for the first time in a non-human taxon that the male's need to balance investment in reproduction against risk taking is reflected in sexual displays. This may be important information for choosy females seeking partners with personality traits that will enhance breeding success. The researchers suggest this may further our understanding of both the use of conspicuous sexual signals in animals, and the deep evolutionary origin of personality in humans.

Citation: Garamszegi LZ, Eens M, Török J (2008) Birds Reveal their Personality when Singing. PLoS ONE 3(7): e2647. doi:10.1371/journal.pone.0002647