THE secret of how birds know to sing in springtime has been discovered by researchers in Scotland and Japan.
A key part of the brain in birds is affected by seasonal change. The team found that, when birds are exposed to more light, cells near the pituitary gland release a hormone that sparks a series of reactions, making them ready for the mating season, when they sing more to attract a partner.
The findings, reported in the journal Nature, could have implications for treating infertility in humans, because they share the same type of cell.
Scientists have known for 40 years that one particular area of a bird's brain is affected by the amount of daylight.
Peter Sharp, a professor of avian reproductive biology at the Roslin Institute, near Edinburgh, was involved in research.
He said: "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."
The study, led by Professor Takashi Yoshimura, from Nagoya University in Japan, used a genome chip – a device used to sift through genetic material – to scan 28,000 genes from Japanese quail.
The birds were exposed to varying lengths of light, corresponding to longer and shorter days. The researchers found that genes in cells on the surface of the brain were switched on when the birds received more light. As a result, the cells started to release a thyroid-stimulating hormone, previously associated only with growth and metabolism. It indirectly stimulated the pituitary gland to secrete further hormones called gonadotrophins, causing male birds' testicles to grow and, as a result, they begin to crow to attract partners.
Prof Sharp said: "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."
He said it would be "very exciting" if such basic research in birds eventually led to a greater understanding of fertility issues in humans.
"It would be a good example of basic botany research opening up new areas of knowledge in humans," he said.
Dr James Pearce Higgins, a research biologist with RSPB Scotland, said: "We've known for some time that there is a relationship between increasing light levels in spring and birds breeding patterns, and this seems to pinpoint the mechanism behind that relationship. This research is particularly interesting given the additional effects of temperature upon the timings of bird breeding – a wealth of studies from across Europe have shown most birds are breeding earlier as a result of climate change.
"Chick food sources are also peaking earlier, and the relationship between the two affects how well particular bird species can respond to increasing temperatures.
"The relative importance of day length and temperature in determining when birds breed will, therefore, influence how well species cope with climate change."