Researchers from Canada, Belgium, Germany, the United Kingdom and the United States used 110 years of scientific data to reveal that bumble bees are not migrating north like some other species as the climate warms, but are losing habitat in the south.
"Bumble bee species across Europe and North America are declining at continental scales and our data suggests climate change plays a critical role in this trend," biologist and lead author Jeremy Kerr of the University of Ottawa said at a briefing.
"The rates of loss are very rapid and are nearly the same across continents."
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.
The study geotagged 420,000 observations of 67 species of bumble bees from 1901 to 2010 and combined information with climate data, land-use data and pesticide-use records.
"This is big data," said ecologist Paul Galpern of the University of Calgary, adding the study's authors are making their data and computer code available to researchers around the world.
After establishing a baseline of bumble bee habitat from 1901 to 1974, the study observed significant changes as climate warming caused by human activity became evident.
The findings, published Thursday in the journal Science, suggest bumble bees are losing nine kilometres of their southern ranges per year and have lost about 300 kilometres of range to date — both in Europe and North America.
The study found that the impact of pesticides such as neonicotinoids, which are known to be harmful to bees, could not account for the sheer breadth of bumble bee population declines.
It also found that bumble bees are migrating to higher, cooler altitudes in mountain ranges including the Rockies, the Pyrenees and the Alps.
"Impacts are large and they are underway," said Kerr. "They are not just something to worry about at some vague future time."
Biologist Laurence Packer of Toronto's York University said among the more than 800 bee species in Canada, bumble bees are key pollinators because they're active from spring until fall collecting pollens from a wide range of plant species.
"So the loss of bumble bees has a far greater impact upon overall pollination rates in the environment than would the loss of a number of other bee species," said Packer.
The study's authors were surprised to find that bee ranges have not shifted north with warming temperatures, unlike many other species — a phenomenon they do not yet fully understand.
Butterflies, which have been extensively studied, have adapted and are surviving warmer southern temperatures while also ranging further north.
Kerr says butterflies evolved from the tropics and have complex biological mechanisms for coping with heat. Bumble bees evolved in cool and temperate conditions and are unable to withstand heat shock.
The study's authors propose immediate international consultations and further research on the possibility of "assisted migration" to move bumble bee species north.
"We may need to contemplate this at continental scales to preserve these species in the future," said Kerr, even while acknowledging there are "ethical implications" in transplanting bees as little as 50 or 100 kilometres outside their usual range.
In the meantime, researchers began a citizen science project last year to further track the bees.
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.
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