Jeremy Kerr, a researcher at the University of Ottawa in Canada, and his colleagues analyzed more than 400,000 observations of bumblebee species collected in North America and Europe from 1975 to 2010. When the researchers recorded the locations of these bee populations, they found that many of the 67 species analyzed were moving northward from their southern limits while the northern edges of the bees' ranges are staying in place. What it results in is obvious. Bees have been paid more attention to in recent years, with populations of honeybees and bumblebees obviously declining in some parts of Europe. Previously, attention on the decline of bee populations has focused on causes including habitat loss, pesticide use and the spread of bee parasites . But the work by Kerr's team found something different. "For every species, there is one or two species declining and others that are not moving at all," says Kerr. This shift has also been observed in other species, such as butterflies. But due to a new cause -- the rise of temperatures instead of total pesticide use, a change in land use or parasites, bumblebees -- unlike butterflies -- have failed to extend the northern boundaries of their ranges into the territory that is now habitable for them, so bumblebee species across Europe and North America are declining rapidly, the latest study led by Kerr's team finds. "Our data suggest that the new factor plays a leading, or perhaps the leading, role in this trend," says Kerr. "This study shows that a fourth factor is also beginning to affect it. It is likely that the combined stresses from all of these pressures will have destructive impacts on bumblebees in the not-too-distant future," says Dave Goulson, a bee researcher at the University of Sussex, Brighton, UK. Exactly what can be done to help bumblebees is not clear. Kerr's team suggests that relocating colonies might be an answer but Goulson says that because the insects are mobile they are capable of moving northwards if there is suitable habitat available. What's the new cause of bee populations' declining according to Kerr?
Habitat loss. Pesticide use. Climate change. The spread of bee parasites.