Literature Review: Threats to Bees and Bats

by Carl Strang

I had been sort of vaguely following the story of problems honeybees have been experiencing in recent years with diseases and parasites. Then I saw a paper in Plos ONE that seemed to reveal progress [Bromenshenk JJ, Henderson CB, Wick CH, Stanford MF, Zulich AW, et al. (2010) Iridovirus and Microsporidian Linked to Honey Bee Colony Decline. PLoS ONE 5(10): e13181. doi:10.1371/journal.pone.0013181].

This hole in a red elm on the Mayslake mansion grounds has housed a honeybee colony for years.

This research group appeared to have solved the mystery of what has been causing collapse of honeybee colonies: a combination of pathogenic organisms, a virus and a microsporidian (single-celled fungus); apparently when separate, these microorganisms are not as devastating.

More recently a review of the problem, apparently written before the Bromenshenk et al. study came out, was released by the Department of Agriculture (CCD Steering Committee. 2010. Colony collapse disorder progress report. USDA Agricultural Research Service). The committee concluded that the disorder is attributable to a combination of factors rather than any single one. Disease organisms, parasites, and pesticides (especially miticides used to treat bee parasites) all may be contributors. Stresses resulting from domestic colony management and transportation practices also are possible contributors. None of this is invalidated by the Plos ONE paper. The immediate cause could be that combination of diseases, but the bees may be weakened by some of the other factors and so made vulnerable.

A separate concern has been raised about the impact of the big windmills used in power generation on migrating bats. Numbers of bats sometimes are found dead beneath those things. Canadian researcher Robert Barclay and colleagues have been looking into this problem, and a pair of papers they published in the Journal of Mammalogy in 2009 presented some of their results. In the first of these (Cryan, Paul M., and Robert M.R. Barclay. 2009. Causes of bat fatalities at wind turbines: hypotheses and predictions. J. Mammal. 90:1330-1340), they found that bat species are not all equally affected. Hardest hit are tree roosters and longer-distance migrants. More research is needed to find what brings bats to the turbines (random encounters, coincidental placement on concentrated travel routes, or attraction to the sound or another stimulus presented by the windmills).

This history-conscious bat is roosting inside Aldo Leopold’s famous Shack. Much of his Sand County Almanac was inspired by that site in central Wisconsin.

The second paper reported the start of this additional work (Baerwald, Erin F., and Robert M.R. Barclay. 2009. Geographic variation in activity and fatality of migratory bats at wind energy facilities. J. Mammal. 90:1341-1349). They monitored bats acoustically across southern Alberta. Bats concentrated their migratory travel along certain routes. Mortality depended on whether turbines were on these routes, and also on turbine height. The last set of data suggests a way to help the bats out through windmill design. Mortality was low on turbines 50, 80 and 84m tall; turbines intermediate between those extremes, at 65 and 67m, produced much higher mortality. Finding where the bats funnel and avoiding those places, and building either short or very tall windmills, can greatly reduce bat kills if these results hold up under further tests.



  1. Gary said,

    February 11, 2011 at 7:16 pm

    Much of the more recent research I’ve seen seems to point to pesticides including clothianidin which has been banned in some European countries already as the primary factor. Have you read anything on this?

    • natureinquiries said,

      February 12, 2011 at 7:19 am

      Hi, Gary,
      There’s been a lot of debate on this in an entomology e-mail list I subscribe to. If it were that simple, I think that it would have become clear. Of course, part of it is the defense of vested interests. Traveling beekeepers don’t want to admit their practices may be contributing factors, pesticide companies don’t want to be implicated, etc. Causes may be different at different times and places. Bees are important for agriculture, motivating a lot of study, and ultimately the research will clarify things. But no impartial, knowledgeable observer seems to believe that any one factor like a single pesticide is solely responsible.

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