Bird brain study sheds light on why they sing in spring

Published on Wed 19 Mar 2008

The Telegraph - By Roger Highfield, Science Editor

The songs that each spring announce when birds are ready to compete for homes and sex have been traced to changes in the brain, according to a study that can shed new light on winter depression in people.

Birds sing in spring to attract mates and signal the boundaries of their patch

While some birds, such as robins, sing throughout the winter, other species of bird take up singing at this time of year again, both to attract potential mates and to signal to other birds the boundaries of their 'patch'.

The birds burst into song in mid January because cells on the surface of the brain trigger hormones when the days get longer, expanding male testes as a result, says a study in the journal Nature by a team led by Prof Takashi Yoshimura of the Nagoya University, Japan, who worked with Prof Peter Sharp of the Roslin Institute, near Edinburgh.

"Although it remains to be proved, several lines of evidence suggest that a similar mechanism might apply in other birds and mammals," says Prof Yoshimura. "We are now working on this question."

Around half a million people in Britain alone suffer so called seasonal affective disorder (SAD), also known as winter depression, which is linked to a lack of light during winter. "We consider that our study may contribute to understand the mechanism of SAD in the future," he says.

While much work has been done on the body clocks that control how creatures organise their lives around the rising and the setting of the sun, this is a seasonal clock and the team studied the key part of bird brains responsible for the launch of breeding.

"The knowledge of a new process that indicates to birds it is the mating season could have implications in our greater understanding of reproduction," says Prof Sharp, "A long way down the line it may even help in treating infertility, for instance by identifying causal gene mutations."

Prof Sharp was the first to identify the area in birds' brains affected by changes in day length 40 years ago, but until now the exact mechanism involved was not known. Advances in technology made it possible to find this seasonal clock.

The researchers used a special gene chip - known as a microarray - to scan 28,000 genes from Japanese quail, which had received varying lengths of light corresponding to short and longer days.

Their analysis shows that the crucial event that triggers the response to long days is the activation of a gene for a thyroid-stimulating hormone called thyrotrophin. This occurs in a brain region called the pars tuberalis, highlighting the significance of this region for activating springtime breeding.

Overall, genes in cells on the surface of the brain were switched on when the birds received more light, and as a result the cells started to release thyroid-stimulating hormone.

A first wave of gene activation occurs roughly 14 hours after dawn on the first day of sufficient length; a second occurs roughly four hours later.

Researchers found that the hormone, which has previously had only been associated with growth and metabolism, indirectly stimulates the pituitary gland to secrete hormones - gonadotrophins - to cause the birds' testes to grow and, as a result, to begin to crow to attract partners.