As we all know, people have personalities. The personality of a person influences the way he or she interacts with other people. Animals also differ in the way they interact with other animals. As people who have pets might recognize, some pets are shy, others are bold. Scientists are increasingly aware of the fact that also animals differ in their personality. However, it remains difficult to quantify the personality of an animal. In the great tit (Parus major), scientists have devised methods to assess the personality of an animal. This provides insight into how animals with different personalities cope with certain situations. But how do you measure the personality of a bird?

In great tits, personality is measured as exploration score. This means that birds that quickly explore new unfamiliar surroundings have a different personality than birds that do not explore quickly. This is measured this by introducing a bird to a chamber which contains 5 artificial trees (for pictures look here). During the first 2 minutes in this unfamiliar room all movements are tracked and used as a proxy for their personality. Birds with a low score did not move much and are generally seen as shy individuals. Birds with high scores moved a lot and visited all the artificial trees, they are seen as bold individuals and tend to be more aggressive towards other great tits.

The personality scores from the laboratory are nice, but what does this mean for the interaction between different males in the field? We looked at males because they are the ones defending the territory. We wanted to see whether there is a relation between the differences in personality that are measured in the lab and the way they interact with other males in the field. To do this, we first measured the personality score in many birds in the lab. We released these birds again in the field. During the spring of 2008 we tested how they responded to an unfamiliar male in their territory. We did this by playing the song of a great tit through a speaker. We scored the response of the bird and related this to its personality. The song of great tits consists of several notes (number 3 in the figure below), which are repeated in a strophe (1). Every bird is able to sing several different songs (A, B, C). We expected that shy birds would stay further away from the speaker and respond by singing while bold birds would come close for an all-out brawl to physically remove that other bird from their territory. What we found was unexpected.

Contrary to what we expected, we found that shy birds came closer to the speaker than bold birds. Bold birds on the other hand stayed further away but responded by singing a different song than before (switching from songtype A to B). This indicated that shy birds responded more aggressively than bold birds. Previous research however found the opposite, there they found that bold birds responded more aggressively by moving in close while shy birds responded by singing from a distance. What could explain these different findings? We noted that the song we used to induce a response was different than what was used in previous research. In short, the song used in the previous research is likely seen as more aggressive by great tits. The reason to respond can differ depending on what you are responding to. Just imagine the following scenario. A small kid calls you a name, you do not really respond because it’s just a kid. If somebody of your own age and size calls you a name you are more likely insulted and will respond aggressively. But if we go even further and a much bigger muscular person calls you a name you might again not respond because you are afraid. So the way you respond to a small kid and a big muscular guy might be the same, but the reason why is very different. So when the signal is weak you do not respond much, with a stronger signal you respond more but with a too strong signal you do not respond again (see figure a below). When we then assume that for each personality this relation between the signal and response is different, then these opposite results start to make sense. When we measure the relation between personality and response with a weak signal, we find slow / shy individuals to respond strongly. Which makes sense, because for a fast / bold individual this weak signal is just not that interesting (the little kid), where for a slow / shy individual this same signal represents the guy of your own size. To the contrary, when we measure the same relation with a strong signal, slow / shy birds are intimidated (as with the big muscular guy) while the fast / bold individuals see that signal as the guy of their own size and respond strongly (figure b below).

So there is a clear relation between the personality of a bird and the way it responds to other birds. However, much remains unknown. Although we propose that there might be a relation between the signal and personality, this relation remains untested. To truly understand the way birds communicate, we really need to understand how their personality influences their behavior towards other individuals.

Jacobs CGC, van Overveld T, Careau V, Matthysen E, Adriaensen F, Slabbekoorn H:

Personality dependent response to field playback in great tits: slow explorers can be strong responders. Animal Behaviour 2014, 90(0):65-71.