A project focused on tree roost enhancement, old growth gap mitigation, and bat-friendly forestry techniques for the forestry industry.

The Project:

Due to cumulative human impacts, including harvest of mature forests, maternity roosts for bats are increasingly limiting on the landscape. This has an impact on reproductive females who need specific microclimate requirements to raise a pup. This project focuses on bat tree-roost enhancement in the Columbia Basin in British Columbia. We are enhancing reproductive habitat for many species of bats by creating simulated old growth trees.  

Trees provide reproductive habitat for more than 70% of BC’s 15 species of bats – and not any tree will do. Different species require different types of cavities, with some species, like the Northern Myotis, a federally-endangered species, depending exclusively on old growth trees to provide the requisite conditions for reproduction.    

WCS Canada is working with multiple partners to integrate critical roosting habitat into ecosystem restoration and enhancement initiatives, using a staged approach to ensure that maternity roosts are immediately available and that they remain available to bats while natural tree roosts recover.   

WCS Canada, together with our partners Okanagan Nation Alliance and Selkirk College, are designing, constructing, and evaluating long-lasting artificial bark roosts. We are using both artificial bark and chainsaws to create bat roosts in trees or using poles, producing crevices of varying sizes and solar exposure, at low and mid-elevations across the Basin to examine bat uptake of these roost creations. Roosts are created in three main ways: 1) wrapping a flexible sheet of artificial bark (approximately 1.25 x 1 metres) around poles or young trees, 2) attaching small sheets of bark (approximately 0.25 x 0.5 m) to the trunk of a live tree, and 3) creating crevices in young trees using chainsaws. In some cases, the tree is ringed to start the process of creating a snag which will naturally develop crevices over time. Our roost tree structures/creations are a stop-gap measure while mature/old forest restores over coming decades.  

At most of our roost tree structures to date, we have installed guano traps at their base to collect bat guano from roosting bats. This guano allows us to assess occupancy and genetic testing identifies the species of bats using the roost. To date (April 2025) we have determined that at least 7, and possibly 8, species of bats use our tree-roost structures/enhancements. This is more species than typically use bat boxes, structures that are now considered appropriate only to use in urban areas or where bats are being excluded from buildings.  

 

FAQs:

In response to some questions we have received from the public who see our structures, we have provided these answers: 

1) What is being done to these poles and trees to make them usable by bats?  

We are creating cavities for bats to roost inside. This is done one of two ways: 1.  installing pieces of artificial ‘flex-bark” onto young trees or onto poles; or 2. Using chainsaws to cut crevices into trunks of trees. Different species and sexes of bats need different solar exposures, and different sizes and shapes of crevices.  

2) How long will these structures last?

The artificial bark is expected to last for many decades, though depending on the structure it is attached to, it may not stand that long. Some poles in some areas are likely to continue to provide a tree-like roost structure for more than 30 years.  

3) How are the trees manipulated?

Professional arborists climb the young trees to create the roost structure. They limb the branches so they can access the tops, and to ensure there are few places for bat predators (ie. owls) to perch near the roost. We leave the tree branches in the vicinity, scattering them around the base to provide coarse woody debris for insects and other biodiversity.  

In some cases, the goal is to create a wildlife tree (eventually a snag), and thus the trees receive two girdles (one wider than the other). This is done by the arborists at the time of limbing to ensure that they die to become a wildlife tree.  One girdle is sometimes sufficient, but there is always a chance of sap filling one and the tree surviving which would be counterproductive to the production of a wildlife tree.  

Artificial bark is attached, to create a cavity under it for bats to roost – this simulates sloughing bark of old/mature trees that are readily used by bats. Additionally, or sometimes instead of applying artificial bark, arborists make two types of chainsaw modifications that we refer to as plunge cuts and simulated lightning strikes.  

If the bark is to be wrapped around the trunk in one large sheet, the tree is girdled. In the case of ‘mini-barks’ where we attach small pieces of flexbark to the trunk, the tree is not necessarily girdled as the small flexbark structures will move with the tree as the trunk expands, and sap filling crevices is not a concern in this type of roost creation.  

4) How is the ‘bark’ attached to the tree?

The artificial bark is a flexible polymer which is wrapped around the tree and affixed with roofing screws. In our pilot structures, we used metal flashing around the top to seal it from water leaking under the artificial bark. But we have now moved away from that; instead, the arborists chamfer the tree which allows the top to be tucked under a lip of bark that acts as weatherproofing.   

5) How are predators deterred? 

Bats naturally are preyed upon by some birds of prey like owls. We limb trees to reduce the chance of providing close perches for predators. We also install the sheets of bark about 2/3 – ¾’s up the tree rather than at the top.  

On poles, we need to mount the bark sheet at the top to maximize height of the roost from the ground. In this case we place a cap of bird spikes (which are a common method of deterring a bird from perching on top of the pole).  

We also install metal flashing around the bottom of poles, and some trees to prevent potential mammalian ground predators from crawling up the pole/tree into the bat roost.  

6) How do you know how many ‘tree roosts’ to create in an area?

Typically, the more tree roosts for bats to select from, the better. Bats have evolved to avoid predators by switching among a suite of tree roosts frequently, and often daily. Bats will switch roosts often when they are raising young to find the optimal roost microclimates for their bodies to produce milk and their pup to stay warm and grow. Bats will reuse the same trees in the same year and between years.   

Our goal is to create multiple roosts in an area. We have created dozens of roost trees in some areas. In other areas, we have installed fewer. In some cases, this is because there are also some suitable old/mature trees in the vicinity, and we are just enhancing what is available. In other cases, we are installing as a pilot to determine use and then return to add additional roosts.  The fewer natural roosts (mature/old trees/snags) already in an area, the more artificial roosts we will need to create in order to make a high-quality roosting area or home range.  

7) What is the wooden framed mesh screening and black box at the base of these structures?

The framed mesh is a guano trap. Bats using the roost tree structure drop guano as they roost during the day. We are using these at most of our roost creations, especially in the first few years of their creation, to determine if bats are using the structures. We can use the guano collected on the mesh to genetically determine what species are using the roost.  

The guano pellets dropping from bats roosting under the artificial bark is more likely to land onto the mesh trap than from bats roosting in chainsaw crevices. This is because guano from bats hiding in the chainsaw crevices may build up in the crevice instead of falling to the base of the tree. For this reason, and to record patterns of bat use over time, we also install a close-range bat detector (black box mounted on base of many roost structures). The bat detector records the ultrasonic signals produced by bats as they echolocate entering and exiting their roost. We can analyse these sound recordings to understand when bats have approached/used the roost.  

Funders and Collaborators:

 WCS Canada is partnering with the Columbia Basin Trust, the Kootenay Connect project of the Kootenay Conservation Program, Environment and Climate Change Canada (Habitat Stewardship Program),  Columbia Valley Local Conservation Fund, the Regional District of Central Kootenay Local Conservation Fund, the Okanagan Nation Alliance, Wildsight-Golden, BC Parks, Nature Trust BC, The Land Conservancy of BC, and many private landowners on this project.  In 2022 we broadened our partners to include the Nature Conservancy of Canada, Valhalla Foundation for Ecology, and the Creston Valley Wildlife Management Area. 

Links to Articles:

Biologists work towards bat conservation in Creston Valley, Creston Valley Advance, November 16, 2022

Kaslo biologist questions logging at unique West Kootenay bat site, The Nelson Star, January 19, 2021

Bats captured in Douglas fir beetle traps, Valley Voice Newspaper, August 13, 2020, pg 12

Artificial old growth trees provide roosts for bats in Golden area, The Golden Star, November 6, 2020.