With climate change, spring is coming ever earlier to the forests of France. Researchers following the roe deer population have found that this shift is causing newborn fawns to miss the moment when new vegetation appears. The lack of resources means fewer of them survive into adulthood, and the population is suffering. The consequences of such a lack of adaptation to climate change are worrying.
Image credit: Gilles Bourgoin
Sometimes, during a deliciously warm spell in late winter, you might see early flowers pushing out of the hard ground, or trees tempted into bud. The unusually warm weather triggers signs of spring, but too early. In the forests of the Champagne region of France, this is now the norm—spring comes a little earlier every year—and baby roe deer are paying the price. Newborns, who still arrive around the same date, are missing the season’s first flush of nutritious new vegetation. A new study, published April 1 in PLOS Biology, shows that the population’s growth rate is suffering.
A group of researchers at the University Claude Bernard Lyon 1 followed the deer population in the Trois-Fontaines forest between 1985 and 2011. Along with the annual temperature increase of 0.7°C, spring came increasingly early to this part of the country, as measured by the flowering of the same vineyards that produce champagne. Consequently, new growth arrived in the forest more than half a day earlier each year, for 27 years. The birth of fawns, however, has not followed the early coming of warm weather and the average date of birth still hovers around 16 May.
The result is that many babies arrive two weeks after the appearance of new shoots, a particularly important food source for nursing mother deer. This nutritional deficit takes its toll on the fawns, many of which never reach the age of reproduction. The researchers tracked the changes taking place in this population by capturing the season’s new babies between April and June, estimating their date of birth, and marking their ears. From January to May, they recaptured the young deer to establish their rate of survival at around 8 months. The results showed that fawns born late in the season – after 31 May – were two times less likely to reach the age of 8 months than those born before 12 May. With fewer adults to reproduce, the rate of population growth is falling (from 1.23 to 1.06).
Some species have proven able to adapt to a changing climate, altering their behavior accordingly. The great tit, a common woodland bird, for example, now lays its eggs earlier, ensuring that the chicks arrive when their caterpillar food source is most abundant. Some mammals, too, have shown similar adaptations. So, why not the roe deer of the Champagne forest? The researchers identified two reasons. First, the animals’ reproductive cycle is tied to the photoperiod, the relative duration of night and day, which is not altered by climate change. And, second, giving birth earlier rather than later does not seem to be a characteristic that is passed down from mother to daughter. The average date of birth in the population thus remains unchanged, while the start of spring moves forward ever more.
If this pattern continues, the roe deer population could indeed decline. The researchers acknowledge that this would take several decades, but these creatures are surely just one example of a species unable to adapt to climate change, and of the potential cost.