More intelligent birds will be stressed less

A new international study relates brain size to the amount of stress hormone in birds. A larger brain increases cognitive ability, which allows them to face new challenges and, ultimately, a more relaxed lifestyle compared to those with a small brain.

Bird species with a larger than average brains have lower levels of a key hormone associated with stress. This is the conclusion of a study in which the CREAF participated that reviewed nearly 200 scientific studies on birds. These birds live less stressed because they know how to anticipate or learn to the most effective way avoid the problems compared to birds with a smaller brain.

"Not all birds respond to stress in the same way," points out Daniel Sol, CSIC researcher at the CREAF. For many years his research team studied, along with other researchers, the differences between species with large brains, such as crows and parrots, and those that have smaller brains, such as the chickens and quails. The first survive better in nature and also have more success when established as a community in a new environment.

In his new work, Daniel Sol, Ádám Lendvai, an evolutionary biologist at the University of Nyíregyháza in Hungary, and other researchers analyzed the scientific literature for studies in which bird corticosterone levels were mesured in situations of stress. In total, they found 189 studies published before 2010 with comparable measures of brain mass and corticosterone of 119 species of birds. The analysis, published in the Proceedings of the Royal Society B, revealed that birds with large brains had lower levels of stress hormone in the blood, while these values are much higher in birds with smaller brains.

A large brain is costly to develop and maintain, but these results suggest that the cost could be offset by increasing the bird’s capacity to face new challenges and stressful situations.

Greater cognitive skills "can be interpreted as an alternative mechanism to hormonal responses," says Sol. After all, he says, "in many species, animal learning has been associated with a reduction in stress."

The stress of life in the wild can shorten the life of birds

Being a bird and living in nature brings with it a lot of stress. Among other risks, in order to survive, birds must constantly detect their predators or endure radical temperatures shifts. These moments of stress cause changes in their metabolism; in particular, it increases the production of a stress hormone called corticosterone. The immediate release of this hormone one or two minutes after a stressful situation triggers an emergency response and prepares birds to react quickly to the threat. However, exposure to the perils of nature and, therefore, high levels of this hormone, has serious health consequences and reduces life expectancy.

Ádám Z. Lendvai, Veronika Bókony, Frédéric Angelier, Olivier Chastel, and Daniel Sol Do smart birds stress less? An interspecific relationship between brain size and corticosterone levels Proc. R. Soc. B November 7, 2013 280 1770 20131734; doi:10.1098/rspb.2013.1734 1471-2954