Song birds take their cue from signals in the brain

Birds know to sing in the spring because cells on the surface of the brain trigger hormones when the days get longer, research published in the journal Nature has found.

Research led by Professor Takashi Yoshimura of the Nagoya University, Japan, involving collaboration with the Roslin Institute, near Edinburgh, has identified how a key part of the brain in birds is affected by seasonal change.

Scientists found that when birds are exposed to more light, cells near the pituitary gland release a hormone that sparks a series of reactions in readiness for mating in the spring, when birds sing more to attract a partner.

While we knew what area of the brain was affected by seasonal change, until now we did not know the exact mechanism involved. Now we have identified a key element in the process of the brain's activity when spring arrives. Such knowledge would have been impossible in the past, but advances in technology enabled us to scan thousands of genes so that we could work out which ones are affected by seasonal change.

Researchers used a genome 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. They discovered that 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.

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

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