Animals colonizing cities are exposed to many novel and potentially stressful situations. Chronic stress, however, can cause deleterious effects. Hence, wild animals would suffer from city life unless they adjusted their stress response to the conditions in a city. Jesko Partecke, Ingrid Schwabl and Eberhard Gwinner of the Max Planck Institute for Ornithology Andechs/Seewiesen in Germany have now shown that European blackbirds born in a city have a lower stress response than their forest counterparts. This reduced reactivity probably has a genetic basis and could be the result of the urban-specific selection pressures to which urban blackbirds are exposed (Ecology 87(8) 2006).
Many species have developed a symbiotic relationship with humans. For example, European blackbirds, European starlings and house sparrows thrive in concrete habitats around the globe. The sparrow is now so closely associated with man that its original niche is unknown, whereas the European blackbird was - as little as 200 years ago - a reclusive forest dweller. These species seem to profit, for instance, by the warmer microclimate and additional anthropogenic food supply in cities. However, they are also confronted with many novel and potentially stressful anthropogenic disturbances, such as the permanent presence of humans, higher densities of cats and dogs, noise and light pollution as well as traffic.
Among the physiological coping mechanisms used by vertebrates - including humans - to ensure survival under adverse environmental conditions is the acute stress response, characterised by the release of glucocorticoid steroid hormones. The acute short-term secretion of these hormones is considered beneficial in that it helps to mediate adaptive behavioural and physiological responses. In prolonged stress situations, however, chronically elevated levels of circulating glucocorticoids can impair reproductive, immune, and brain functions. Thus, wild animals would suffer from
Contact: Dr. Jesko Partecke