Every Individual is Different – Biologists explore the individual behavior of small mammals

In the ancient fables of the Greek poet Aesop, animals have a character. The rural mouse is careful and has problems being around people. The urban mouse, on the other hand, is used to this stress; it is curious and courageous. But what does biology say about this? Is there something like an animal personality? Animal ecologists Prof. Jana Anja Eccard and Dr. Melanie Dammhahn have been studying the behavior of small mammals for years. Their research shows that animals of the same species have different temperaments.

The call of a crane sounds over a vast green field, rabbits off in the distance; a peacock butterfly flutters under the cloudless sky. Bornim is an idyllic village in Brandenburg. “This is where we do outdoor biology,” say Jana Eccard and Melanie Dammhahn. The behavioral ecologists conduct their experiments in a fenced area in the middle of the field under the natural living conditions of the vole. This includes its bird of prey as a natural enemy and its food of grass, seeds, and insects. The University of Potsdam has leased three hectares of land in Bornim. The researchers regularly observe the behavior of native, wild populations of different vole species, such as bank voles and common voles.

Biology has recently become interested in the individual character of animals

Eccard is certain that “even among conspecifics, there are great differences in behavior.” Different, recurring behavioral patterns can be identified – a result of evolution. The personality types have evolved over generations to adapt to various environmental conditions and may also be genetically anchored. Biology has long neglected behavioral differences within a species, though. Until recently, temperament had been considered a purely human category. “For decades, biologists have statistically neglected variability in animal behavior. They were interested in averages and not in the differences within a species,” Eccard explains. “But at some point they accepted that animals are different.” She assumes that even plants will be soon examined in their individuality.

In order to find out how different types of behaviors interact with environmental factors, the biologists assembled artificial populations of conflicting personality types in the Bornim meadows: active and reserved voles, fearful and bold ones, aggressive and peaceful ones, explorative and less curious ones, those that want to be close to their conspecifics and those who tend to avoid them. “These behavioral traits are based on the concept of five personality traits which is often used in psychology,” the professor explains. For each species, there are again individual taxonomies of personality traits, depending on whether the animals live in social groups or have their individual territories.

The personality traits can be determined based on the animals’ usage of space. “How an animal moves in an unknown territory says something about its personality,” Dammhahn explains. This is why we equipped each vole in the field with a transmitter. The researchers can record the activity of a vole with an automated telemetry system. Does it interact with other voles? Does it move in small steps or big jumps? Does it move in a large or small area? Does it like to explore new spaces, or does it prefer to stay in a familiar area? Based on this information, the biologists and young scientists from the research training group “BioMove” gain insight into individual animal behavior. "The brave voles have larger areas to roam and, thus, better access to food,” says Dammhahn. “On the other hand, they are less thorough; they do not stay in one place and, in turn, miss out on opportunities to find food.”

Shy voles learn more slowly than brave ones but are more flexible

Behavioral studies show similar results. Initially, you see no voles in the 50 cages with lots of litter, hay, food, and drinking bottles. The animals hide from potential predators. How quickly they get used to people also depends on the individual behavioral type. “We already know from a study done by our peers that it is easier to domesticate courageous than careful animals, because they are less stressed when dealing with humans,” Eccard says. “Bold voles learn faster.”

To determine whether a vole is more courageous or shy, the experimental animal ecology experts use, for example, the “open field” test. Does the vole venture into in the open center of the field of a fenced area, or does it move close to the edge? The researchers also place the rodents in a dark tube and measure how long it takes them to venture out. In another personality test, bank voles must learn the way out of a labyrinth. Two different fruit scents indicate either an exit or a dead end. Once they have learned to associate the fragrance for the exit, the animals should relearn that now the other fragrance leads to the dead end or vice versa. What happens?

More active rodents learn to use the first fragrance as a guide very quickly, but after changing the association they hold on to what they have learned and keep running into the dead end. Careful and less active animals take much longer to use the scent as a guide. After that, they can quickly adapt to another fragrance. “Our study shows that bold individuals like making quick but often wrong decisions in new situations while those who are cautious think longer but are able to use what they learned more flexibly and in the long term,” says Eccard. The animals’ sex plays a role in the experiments: females are better able to learn than males.

The human factor shapes the animal personality

The animals’ individual behavior is also influenced by humans. A landscape shaped by humans changes the animal’s personalities in a population. Some behavioral types are able to cope better than others. “That is true for badgers, for example, whose pulse increases when they hear human voices,” Dammhahn explains. The behavior of other animals is also directly influenced by humans. In the group, a PhD student with a scholarship from the German Federal Environmental Foundation is currently researching the influence of light on animal behavior. “In Europe, all street lights are being replaced by LED lights,” the professor explains. “We already know that this bluish light changes human sleep rhythms.”

The PhD student wants to find out with her experiments whether this is the same in native voles. “We placed small LED lamps on a vole-inhabited area,” Eccard explains. “While the animals usually have the same biorhythm, there were no more synchronous resting periods.” This may have consequences because the voles of a population usually go looking for food at the same time. Voles that leave the burrow individually risk becoming prey to owls. Joint activity and resting periods are essential for survival. The effects of artificial light on insects are equally dramatic. “If all the beetles are bustling around a street lamp, they become easy prey for predators like toads or weasels.”

Behavioral types can be detected not only for voles but also for insects. The behavior of fire bugs has been tested by Hungarian scientists with a similar test setup that was used for small mammals by the Potsdam researchers. When placed in a dark tube, not every bug immediately starts running to explore its surroundings. Some need more time than others, depending on the individual bug’s genetic disposition and experiences. For behavioral researchers, consistency in animal behavior is important: They test the individual repeatedly over a longer period to find out whether it retains a behavioral trait – and it actually does in most cases. “A shy fire bug larva is also careful as a fully grown bug,” says Eccard.

Bold bank voles have more offspring than shy ones

And what distinguishes an urban mouse from a rural one? The biologists investigate this in the middle of Berlin: directly on the freeway under a bridge near Berlin’ exhibition center. The researchers conducted another open field test here, and common voles again played the main role. They also live in the metropolis. “Biodiversity is even greater in Berlin than in Brandenburg,” explains Dammhahn. Agricultural use creates one-sided habitats, and the use of pesticides minimizes the food resources of many small mammals. The capital with allotment gardens, green roofs, parks, ponds, and forests offers a wide variety of biotopes.

On the other hand, though, the human ubiquity in a city puts the animals under permanent stress, which, in turn, affects their personality. The results of the open field test in Berlin have shed new light on the old fable of rural and urban mice. “The Berlin voles seem to more courageous than their counterparts in the Uckermark region,” Dammhahn says. Particularly interesting: A bold male bank vole has more offspring than its fearful conspecific – at least in the summer. “In the spring or fall, however, the cautious animals might be more successful. We’ll be looking into that.” It's also clear that brave voles die earlier. They live more dangerously. So who has the advantage – the shy vole or the brave one? “Both behavioral types have their advantages and disadvantages,” says Eccard. “They wouldn’t exist side by side otherwise.”

The Researchers

Prof. Jana Anja Eccard studied biology and sociology. Since 2008, she has been Professor for Animal Ecology and Human Biology at the University of Potsdam.

Dr. Melanie Dammhahn studied biology. At present, she is Interim Professor for Animal Ecology at the University of Greifswald and visiting scholar at the University of Potsdam.

The Research Training Group BioMove researches the effects of the movement of organisms on the biological diversity in dynamic agricultural landscapes. BioMove is a joint project of the University of Potsdam the Leibniz Institute for Zoo and Wildlife Research and the Leibniz Centre for Agricultural Landscape Research. It has been funded by the German Research Foundation (DFG) since 2015.

Text: Jana Scholz
Translation: Susanne Voigt
Publsihed online: Alina Grünky
Contact to the online editorial office: onlineredaktionuni-potsdamde