Forty years ago, near Florida’s Ocala National Forest, I took the photos seen in today’s blog. This is a bumblebee nest, accidentally uncovered and exposed on the forest floor, in the winter of 1974 in central Florida. You can see a few bees and about 90 cups, or pots, built by them. The pots hold pollen, nectar, and future generations of bees. If today’s news about bumblebee habitat is true, you might not find these particular insects in that particular woods anymore.
A study published in the journal Science (and reported by the New York Times, Time magazine, CTV, and Globe & Mail among many others) warns that the warming climate is making life miserable for bumblebees. The paper, with Jeremy Kerr and Alana Pindar of the University of Ottawa as principle authors, relates that some species of northern hemisphere bumblebees have lost 300 kilometres of southerly range. The researchers believe this is most likely due to climate change. As the climate warms up, certain plants disappear or are crowded out by invaders. It is also possible that warmer days hinder the bees’ mating or foraging abilities. One would expect that the bees would simply spread further north to take advantage of new locations that become warmer and habitable. But that doesn’t seem to be happening.
Unfortunately, most bumblebee species do not reproduce nor spread fast enough to head northward into new habitat. Instead, the bees are being trapped, or “squeezed in a vice” (as Dr Kerr describes it) – unable to populate areas to the north, unable to continue to live in areas to the south.
By examining nearly half a million scientific observations of 67 species of bumblebees from the past 109 years, the authors of Climate change impacts on bumblebees converge across continents have presented an overwhelming indictment of our likely future. Their study may be the most in-depth analysis conducted so far on the impact of climate change on an entire complex group of important native species. This is a “big data” study and nothing like it has been done before.
This was indeed a comprehensive analysis. Only observations that definitively identified species and placed them in documented locations at specific years comprised the 423,000 geotagged data points. The 67 species of bumblebees were mapped and their changing territories were noted over the years. For each of the sightings, the species, year and location was noted. For most species, range of habitat is significantly shrinking.
The 14 scientists involved in the study were determined to discover the cause of the diminishing bumblebee range. With such a huge data set, it was possible to learn that pesticides and urbanization (paving over forage and nesting sites) were not significant causes of the plight of the bumblebees. For example, the study found that the use of neonicotinoids, which can be harmful to bees, does not account for the widespread loss of bumblebee range. Instead, climate change was correlated as the most consistent cause of the bees’ shrinking territory. Within the bumblebee habitat, the average temperature increased 2.5 degrees Celsius during the century investigated. That’s bad news for bees.
Unfortunately, the bumblebees are not migrating north quickly enough to maintain the size of their former range. Although new potential homelands are heating up, bumblebees don’t move fast enough to keep up with the changing climate. The bees become our polar bears, adrift chunks of ice, clinging to what they know, unable to move to safer places. To migrate 300 kilometres in 100 years, the bees would need to colonize new territory at a rate of 3 kilometres (2 miles) each year. But bumblebees do not migrate in hefty swarms the way their honey-making cousins do. Honey bees may send colonizing swarms a dozen kilometres. We know this from observations of honey bee swarms crossing lakes, and also from the intrepid settlements established by Africanized honey bees which traversed 9,000 kilometres in 30 years during the last century. Bumblebee biology is vastly different. At the end of each season, all the workers die. Then a few mated queens establish new colonies, typically within a few hundred metres of the preceding year’s nest. Bumblebees are not known to conquer vast stretches of new habitat.
Instead of spreading rapidly northward, bumblebees are mostly stuck in their ancestral settlements. The only real exception to that is an upward migration – in the study some species of bumblebees were discovered migrating to higher elevations (hills and mountains) where that option was available. The Kerr, Pindar, et. al., paper showed that after a 300-metre elevation gain, some species began to occupy better terrain. Apparently, an elevation rise of 300 metres may equal a climate change found by traveling 300 metres north. But it is much easier for bumblebees to relocate 300 metres higher up in a hundred years than to fly 300 kilometres north.
Short of reversing climate change, other methods of saving the imperiled bumblebees are being considered. One possibility is assisted migration.
Assisted migration would involve relocating enough bumblebees to a new habitat so that the reproductive viability of the insects is ensured. The relocations would be further north in ecological niches that are similar to the bees’ former, but disappearing, habitats. In this scheme, the bumblebees would be scooped up, loaded into vans, seat-belted if necessary, and then released in better pastures.
Unfortunately, artificial assisted migration is a more likely fix for the plighted bumblebees than a return to a cooler climate.