Scientists propose international effort to assist bumblebees to migrate further north after study finds rising temperatures linked to their decline

A comprehensive study of bumblebees across two continents over the the past century has unequivocally linked their decline to rapidly rising global temperatures resulting from man-made climate change, scientists have said.

A detailed review on reported sightings of 67 different species of bumblebee across Europe and North America between 1901 and 2010 has indicated that the key pollinating insects of crops are being squeezed “like a vice” by rising temperatures.

Over the past 40 years, when the greatest temperature increases have occurred, the bees have been effectively pushed out of the southern ends of the natural ranges but they have failed to compensate for this loss of territory by migrating further north, the scientists said.

“One of the most striking things is that the trends we have found were often indistinguishable between Europe and North America. Bumblebee species are responding similarly across continents from 1975, a time when climate change really began to accelerate,” said Paul Galpern of the University of Calgary in Canada.

The study found that the home territories of 67 bumblebee species have been compressed on average by up to 300 km on both continents, increasing the pressure on these critical crop pollinators that are vital for food production are also suffering from habitat loss and the use of agricultural pesticides, the researchers said.

The results of the study, published in the journal Science, have so alarmed scientists that they have proposed an international rescue effort to assist different bumblebee species to migrate further north, if possible, in order to extend their diminishing home territories.

“If we are to conserve species such as bumblebees in the future it is possible that we will need to intervene in a significant and extensive way to help them to adapt,” said Jeremy Kerr, professor of biology at the University of Ottawa who took part in the analysis.

“There are ethical implications in term of taking species and translocating them dozens or hundreds of kilometers further north that we need to consider....We should not do that without considering the impact on existing species in those locations,” Professor Kerr said.

Although the scientists have not been able to prove that rising temperatures are the direct cause of the loss of southern habitat range, there are strong circumstantial reasons for believing this is the reason, they said.

However, the most puzzling and worrying aspect of the study is that bumblebees species living across a vast area of the northern hemisphere are not moving to cooler areas further north, although some are moving to higher elevations up mountain-sides.

“They just aren’t colonising areas and establishing new populations fast enough to track rapid, human-caused climate change. This is despite warming in these areas of about 2.5C or slightly more on average across their northern range,” Professor Kerr said.

The study was based on more then 420,000 records of bumblebee sightings for the 67 species, which began at the start of the last century. The scientists were able to compare the geographical spread of each species over time, which showed a significant shift north from the original southern boundaries, but no corresponding extensions of the northern habitat boundary.

“Many other species, such as butterflies are expanding north into new areas, so bumblebees are doing something quite different. At the same time, however, the southern and hottest edges of their geographical ranges are collapsing inward,” Professor Kerr said.

“We already know that extreme heat for example in southern Europe has wiped out local populations of some bumblebee species and in this study we have shown that this mechanism may be operating across two continents to crush bumblebee species in a kind of climate vice,” he said.

“This is a huge loss and it has happened very quickly. We are looking at rates of loss of about 9km per year in those southern areas and these effects are consistent across continents. Again, many other species are doing something quite different,” he added.

The study also investigated the role of pesticides, and in particular neonicotinoid insecticides, on bee decline in the US, but found no significant link to the observations of retreating territories. “Some of the climate responses reported in this paper began to appear before the use of neonicotinoids,” Professor Kerr said.

However, the researchers did find that some bumblebees were moving to higher altitudes to compensate for rising temperatures - supporting the view that warmer temperatures are responsible for the loss of southern territory.

“This is the first time that a large group of organisms across continents has been analysed in this way and shown to be shifting up or down in elevation depending on where they are found,” Professor Kerr said.

“This is an independent way of verifying that these species are at serious and immediate risk of human-induced, rapid climate change. The impacts are large, and they are underway. They are not just something to worry about in some vague future time,” he said.

“Our results indicate that human-caused climate change is a significant factor in the decline of bumblebee species across continents. We may be able to manage some of the declines for a time....Bumblebee species may need human intervention to help them establish populations in cooler and more northerly environments,” Professor Kerr said.