Christoph Steeger worked for over 30 years as a wildlife biologist in British Columbia. Now in retirement, he’s engaged in wildlife conservation on Vancouver Island. His most recent project is developing a habitat stewardship program for bat species at risk in collaboration with Quw’utsun Cultural Connections Society in the Cowichan Valley. Part of this project is the conservation of large, old cedars as these trees have important Indigenous cultural values, as well as providing valuable habitat for bats.
The following is an edited transcription of our phone conversation.
Dave Flawse: What are some challenges facing bat populations on Vancouver Island?
Christoph Steeger: They’re running out of natural habitat. We’re talking foraging habitat – primarily areas with abundant insects – and roosting habitat, which for the bat is trees. Some species go into rock crevices and caves, some use anthropogenic structures such as attics, barns, or bridges. But the vast majority, 13 out of our 15 provincial bat species, use trees for roosting. At least that is what they did when our forested landscape was intact.
The main purposes for roosting in trees are resting (day and night), raising young in communal maternity roosts, and winter hibernation. Day roosts are sites where bats rest during the day in spring/summer/autumn while night roosts are rest stops between foraging bouts. Maternity roosts are important for adult females during reproduction; they are called nursery roosts when groups of females give birth and raise their young in a cavity together.
An open question for bat scientists is: “How many bats actually overwinter in BC?” Because our bats were always thought to be migratory, but with climate change, and perhaps for other reasons, it’s believed that more and more bats overwinter here. So, the disappearance of habitat trees, or roost trees, is a major concern for bats. And it’s not just for the bats, but for all the wildlife-tree users. Deforestation of the old forests is one of the biggest threats to bats around here.
How successful in helping bats are initiatives like installing bat boxes?
That depends on several factors, such as presence of bat species that use man-made bat houses (big brown bat, little brown myotis, and Yuma myotis), bat house design, exposure to the sun or shade (bats are very temperature sensitive), height above ground, and surrounding habitat. I’d like to point out that bat houses are not meant as substitutes for natural habitats and can do more harm than good for bat communities. According to the Western Bat Program of the Wildlife Conservation Society Canada, the best use for bat houses is to replace lost building roosts in urban areas.
I have a feeling a lot of bat boxes out there are empty because people don’t know well enough what is important to the bats. When a bat chooses a tree for roosting, they naturally know what to look for. There are many microsite considerations for the bats such as temperature, safety from predators, and easy access to the roost.
The bats know the safest and climatically the most appropriate roost site for them. People don’t necessarily know that when installing bat boxes. While well-intended, a bat box might be set up in a wrong spot and the bats will never use it.
Organizations like the Wildlife Conservation Society Canada, Community Bat Programs of BC, or Bat BC are starting to question the value of bat boxes. They do not compensate for the disappearance of habitat of roost trees in the natural environment.
Besides bat habitat, what are some other benefits of leaving snags in the forest?
Bats are just the tip of the iceberg – many forest wildlife species are dependent on snags. In the 1980s, forest researchers in the US Pacific Northwest, and later in BC, discovered that there was a systematic, grand scale elimination of snags from the forested landscape. And they found that there are many animals that depend on dead, dying, defective, and decaying trees – such trees are known as wildlife trees. About 80 wildlife species in BC (17% of all terrestrial birds, mammals, and amphibians) depend on wildlife trees. That’s a big percentage.
Often when I talk about this, it surprises people. It is not generally known that aside from woodpeckers, chickadees, and nuthatches (the excavators of tree cavities), there are other species such as squirrels, weasels, bluebirds, swallows, small owls and falcons, and black bears that require tree cavities. Even several duck species raise their chicks in tree cavities: the wood ducks, buffleheads, goldeneyes, and mergansers. So, wildlife trees are extremely important habitat for cavity-using animals.
But it doesn’t stop there. Leaving standing dead or defective trees is only the beginning of the after-life value of trees. Eventually a snag falls to the ground and becomes a log that has habitat value, such as protective cover for small mammals (mice, voles, shrews), amphibians (frogs, toads, salamanders), and reptiles (snakes). After the log has decayed, it becomes part of the soil that gives rise to the next generation of trees and the cycle repeats itself.
Lastly, I want to mention that snags in a forestry, rural, or urban residential setting can be a danger to people and property. That is why the provincial Wildlife/Danger Tree Assessor’s Course was developed and has been taught for over 30 years. It is administered by the University of Northern British Columbia Continuing Studies Program. Through this three-day course, people can get certified to assess snag-related hazards and wildlife values, and determine which snags are safe and should be left. This is one way to assure that wildlife tree habitat remains in our environment, to maintain the many species that depend on it.
Dave Flawse tells stories at the intersection of history and science. Follow his work exploring Vancouver Island’s history at www.vancouverislandhistory.com.
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