Kerr and his colleagues looked at historical records of the habitat ranges for 67 bumblebee populations in Europe and North America between 1901 and 1974, when climate warming was negligible, and between 1974 and 2010, when climate change accelerated.
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“These species are at serious and immediate risk”. Warming temperatures in the north, however, have pushed mountains’ treelines to greater altitudes, robbing bumblebees in northern mountainous regions of the wildflowers they rely on for food.
“Bumblebee species play critical roles as wild pollinators, not just for crops but of all sorts of plants”, says Galpern. Another possible culprit is more surprising: some bumblebees are kept for commercial purposes to fertilize indoor greenhouses that grow products like tomatoes, which they do more effectively than honeybees.
Researchers have not determined just how many bumblebees there still are or how many have died.
Bees are being crushed in a kind of “climate vice”, said Kerr, the university’s research chair in macroecology and conservation, quickly losing the ability to survive on the southern edges of their ranges while being slow to move north.
People are encouraged to photograph bumble bees and send the photo to bumblebeewatch.org, where the species will be identified and added to a map of North America.
Kerr said he did not know why the bees are failing to move. The study, which was published today (July 9) in the journal Science, did not show any correlation between land-use practices or pesticide use and bumblebee populations.
To conduct their study, the scientist drew on geo-referenced databases from museum collections on both continents. “We are simply losing the southern populations”. The bumblebees that are in decline were doing fine 50 years ago.
Bees are dying out in the southern end of their range because of the rise of extreme heat waves. “They may be running out of options”. “They just aren’t colonizing new areas and establishing new areas fast enough to track rapid, human-caused climate change”.
[READ: Pope Francis Encyclical Calls on “All Humanity” to Halt Global Warming].
The steep decline of bumblebees on a continental scale threatens food security and the economic viability of some crops, the researchers said. “That is an experiment we should never have started”. “We know that such factors can seriously harm pollinator species – there is no doubt about that – but those factors appear to be unrelated to changes along the margins of species ranges in Europe or in North America”. “Bumblebees are not, and we thought they would”. Kerr’s team suggests that relocating colonies might be an answer, but Goulson says that because the animals are mobile they are capable of moving northwards if there is suitable habitat available. “Clearly bumblebees are pretty good at getting around”, Kerr said at the press conference, since they can fly. “They provide an important service to ecosystems”. In the meantime, there are some actions humans can take to try to help out their struggling populations. But unlike butterflies, bumblebees have failed to extend the northern boundaries of their ranges, into territory that is now habitable for them due to climate change, the latest study finds. It’s unclear whether other pollinators, such as other wild bee species or butterflies, could adequately step up to fill the void left behind by bumblebees in these cases.
So far, says Bartomeus, the most common bumblebee species seem to be the most resilient.
Nathalie Pettorelli, a research fellow with the Zoological Society of London, and who was not involved in the research, said in order to save the bees, scientists will need to figure out why they can’t move north.
For now, gardeners can help bumblebees by adding wild flowers to their yards, the researchers say.
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A buff-tailed bumblebee lands on a catmint flowers, sipping nectar and moving pollen from one plant to another. The insects are loosing the battle against habitat loss caused by humans. “It is likely that the combined stresses from all of these pressures will have devastating impacts on bumblebees in the not-too-distant future”. “We have strong evidence presented in this paper to show that this is correlated with changes in temperatures – in climate – across the two continents”.
