The lengthening of days in late winter is an important signal that stimulates the reproductive activity of many animals. Animals living in the milder climatic conditions of southern Europe usually begin breeding earlier in spring compared to animals living in colder habitats further north. Scientists from the Max Planck Institute for Ornithology and colleagues have now discovered that day length affects gene activity differentially in the brain of great tit populations from central and North Europe. This is particularly important because climate change has resulted in warmer temperatures in spring, and therefore day length has become a less reliable signal for the coming of spring. Since warmer spring temperatures also cause the insects that the birds need to feed their young to be available sooner, birds will have to change their breeding schedules accordingly.

Many species across the globe use seasonal information to coordinate important events like reproduction with the conditions in their surroundings. Until recently, however, the exact internal processes and tissues in the brain involved in this response have remained elusive. Thanks to recent studies on domesticated species like rodents, sheep, goat and quail, scientists have successfully identified the genes and the parts of the brain that are involved in the response of an organism to changes in day length.

However, for Nicole Perfito from the Max Planck Institute for Ornithology intriguing questions remained unsolved: "Domesticated species have been bred for commercial purposes, and can breed at almost any time of year. Do wild species, which have to adapt their reproductive cycles continually to the seasonal changes in nature, possess the same mechanisms? And how would such mechanisms allow populations from various habitats to use different day length thresholds to get ready to breed at the right time of year?"

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