High metabolic rates and low temperatures were associated with high risk-taking behavior in birds

The readiness to take a risk is to a great extent influenced by external circumstances. A recent study showed that men living singly are more risk-prone than those living in a steady relationship. Individual differences in risk-taking behavior are present not only in humans but also in other vertebrates and even in invertebrates such as the Beadlet anemone. However, not only external factors can explain these differences in behavior, but also the basal metabolic rate of the body. For example, in great tits there are large individual differences in basal metabolic rate are consistent over extended periods of time (e.g. years).

A team of researchers from the Max Planck Institute for Ornithology in Seewiesen now found in a long-term study in great tits a relationship between risk-taking behavior and metabolic rate. Moreover, they investigated how risk-taking behavior depends on environmental factors. Within the study period of two years they were able to determine the behavior and metabolic rate of 184 individual great tits from 12 populations between two lakes in Upper Bavaria, the "Ammersee" and the "Starnberger See." The birds were captured when roosting inside their nest boxes and brought to the lab to measure metabolic rates. The birds were then equipped with passive transponders, so-called "pit-tags," and released back to their territories. There, the researchers installed bird feeders that were fitted with antennas connected to radio frequency identification readers to monitor the movement of great tits. In order to monitor risk-taking behavior a stuffed model of a sparrowhawk was presented next to the feeders accompanied by playbacks of great tit mobbing calls. With the aid of the transponders, the researchers were able to measure the time that the birds needed to return to the feeder after the disturbance. This measure was then used as a measure for risk-taking behavior for further analysis.

As a next step the researchers investigated how all these factors were related to each other by means of complex statistical analyses. They first found that the great tits differed in metabolic rate, body mass, and risk-taking behavior between both study years; in the year when birds had higher metabolic rate, they also showed higher levels of risk-taking behavior. Additionally, within each year, birds with higher metabolic rates returned to the feeder sooner after being presented with the predator disturbance. Amazingly, ambient temperature also had an influence on overall risk-taking behavior; birds tended to take more risks when temperatures were lower "This study shows that variation in risk-taking behavior is linked to differences in energy constraints. Birds facing higher energetic constraints -- either because they have a higher metabolic rate or because low ambient temperatures cause them to spend more energy on thermoregulation -- are more willing to forage under "risky" conditions, like when a predator has recently been observed in the area," concludes Kimberley Mathot, first author of the study. Possibly birds with a high metabolic rate simply cannot afford to delay feeding because of their higher energetic needs, and thus are more willing to take risks.