City slicker or country bumpkin: City-life changes blackbird personalities

It's something pet owners have always known: animals have personalities too. More than 100 species have so far been identified by scientists where individuals consistently follow distinct behavioural strategies and behave in similar ways in a variety of situations. Scientists believe that such differences may also be important in adapting to new habitats.

Urbanization has considerably changed the living conditions of many wild animals. Animals living in urban areas need to cope with new anthropogenically-altered living conditions. A textbook example is the European blackbird (Turdus merula). Historically a forest-dweller, the blackbird is now one of the most common bird species found in our cities. In these new habitats, the blackbird has changed its behaviour in many ways: urban blackbirds migrate less in the winter, breed earlier, and live in higher densities than their forest conspecifics.

Cities might be also responsible for fundamental changes in the behaviour of wild animals across the globe. A team from the Max Planck Institute for Ornithology in Radolfzell analysed existing studies on differences between urban and rural populations of various species. In 27 out of 29 studies, animals in the city responded differently to new stimuli than animals in the countryside. "This seems to be a global phenomenon," comments Ana Catarina Miranda, the lead author in the study.

Moreover, the Radolfzell scientists tested whether or not these behavioural differences also reflect different personality types and if so, whether this is a result of evolutionary changes or individual flexibility.. To this end, the scientists collected nestlings from an urban and a rural environment, hand-reared them and kept them individually under identical conditions. When these blackbirds matured into adults, the researchers repeatedly presented individuals with unfamiliar objects over a period of several months.

Compared with birds from the forest, the birds from the city waited much longer before they approached a new object. Not only did urban blackbirds react more cautiously towards new objects, they also tended to avoid unfamiliar objects. Since all the birds were collected as nestlings, hand-reared, and kept under identical conditions during the entire experiment, the differences in behavioural responses between urban and rural blackbirds seem to be intrinsic and not a result of experiencing the original urban or rural environments. A recently published study supports these findings: Genes which are believed to be involved in shaping personality traits exhibit a different structure in urban blackbirds than in their rural counterparts.

This work is an important step to understand how animals cope with our urbanizing world. Different reasons might be behind differences in personality types between urban and rural animals, and this is a question to be further explored. "Animals in fast-paced urban environments face numerous and potentially dangerous new situations, and this might select for specific reactions towards novelty," suggests Miranda. "Evolution appears to have favoured certain personality types."