Shy birds may fare better in competitive conditions, as new research from the Max Planck Institute for Ornithology has revealed that exploratory, aggressive West European great tits have a reduced chance of survival when facing competitive, densely populated situations.
Exploratory behavior is a heritable trait, and therefore underlies natural selection pressures. Explorative great tits are more inclined to take risks and rise to a higher social rank. While it might seem that those individuals would fare better in competitive environments with limited resources, risky behaviors require more energy.
Surprisingly, great tits are able to anticipate future breeding densities, but instead of slowing down to reserve energy in competitive situations, exploratory birds take more risks when facing increases in population density between years.
Furthermore, researchers found that exploratory individuals are less likely to survive competitive environments, as they are less able to anticipate and adapt to changes in their social environment.
A group of researchers spent the last four years regularly controlling 600 nest-boxes in 12 woodlots in order to calculate densities within and between bird populations. Next, the birds' exploratory behavior was analyzed based on the total number of flights and hops they took within the first two minutes of arriving in what researchers call a "novel environment room."
"The density effect on the different personality types was amazingly strong," said Niels Dingemanse, study leader from the Max Planck Institute for Ornithology.
For example, the survival rates of fast explorers decreased with increasing population density, while the survival rates increased for slow, shy explorers.
"Our data show that great tits are able to anticipate future breeding densities as they are able to change their exploratory behavior between years," added Marion Nicolaus, first author of the study.
In other words, the birds are able to calculate the competition for breeding space for the upcoming spring, as early as the fall before. For instance, if there is a lot of food available in the autumn, the odds are that more birds will survive the winter, resulting in larger spring populations than if there were limited food sources.
However, exploratory birds were not able to adjust their behavior appropriately, which could explain why natural selection favors a mix of personality types, rather than just one single type of behavior.
"Whether this potential loss of personality variation affects the adaptive capacity of populations is currently unknown but represents an important question in both the social and natural sciences," Dingemanse concluded.
Their findings were published in the Feb. 29 issue of the journal Ecology Letters.
