We are in the process of replacing the temporary plastic fences that
lead frogs and salamanders to the entranceways of the culvert.
Straight-walled plastic sheeting was not
ideal. We watched Northern Pacific Treefrogs, juvenile Rough-skinned Newts and
Western Red-backed Salamanders climb over it on several occasions, and we
frequently needed to patch it (although, it fared surprisingly well over the
past 3 years).
Deciding on a more effective and durable fencing design was a
matter of checking out what other folks had tried, and testing to see which
options would work for our local species. We chose four different types of materials that have been used to reduce road
mortality of frogs and salamanders in other places in Canada.
We tested to see whether our local species - Northern Red-legged Frogs, Northern Pacific Treefrogs, Northwestern Salamanders and Rough-skinned Newts could be contained within fence enclosures made of each material.
We compared the frequency of climbing
and escape behaviour by each species from each type of enclosure. We observed this behaviour using time-lapse photography with wildlife cameras.
The fabric and both types of solid fencing were more
effective than plastic mesh. Northern Pacific Treefrogs escaped
from the plastic mesh enclosure 43% of the time, much more often than the other
types of enclosures.
Red-legged Frogs, Northwestern Salamanders and
Rough-skinned Newts were able to climb further up the walls of the plastic mesh
than the other materials but were rarely able to maneuver around the
overhanging lip.
Based on these results and the relative ease of installation along uneven terrain, we chose the polypropylene fabric as the best material for our new fences.
Instead of being straight-walled, the new
fence has an overhanging lip, to stop those amphibians with specialized toe pads from climbing over the top!
We are using fabricated plastic wood for
the upright stakes and cedar for the top rails. These should last a long time in the rainforest.
The trickiest part of the installation is
keeping the fabric smooth. Sections are cut to fit along each segment of the
sloping terrain. Overlapping pieces are attached to the rails and stakes with
washers, screws, and staples.
The fabric is folded and buried under
ground so that salamanders cannot burrow beneath it.
The final touch will be to add a cone of
mesh on the backside of the fence every few meters to allow animals to climb
over from that direction. We only want the fence to provide a barrier to keep
animals from getting onto the road, not off it!
The Habitat Conservation Trust Foundation and Clayoquot Biosphere Trust provided funding to test different types of materials. Support for building the new fences is from the British Columbia Ministry of Transportation and Infrastructure.
Of course, we are now thinking about ways to ensure that the new fencing will work as intended. We will continue to monitor amphibian movements through the tunnel and devise a way to see what happens when frogs and salamanders encounter the fence!
Yesterday, we were delighted to show our new fence design to a film crew for a documentary series called “Striking Balance”. The SPLAT project will be included as part of their production on how people are working to find innovative approaches to living in harmony with nature in the 16 UNESCO Biosphere Reserves across Canada.
