Tue, 30 Jan 2018

Update on the Fisher Den Box Project

Can’t get enough fisher footage? HCTF project leader Larry Davis has put together another video update on the artificial den box project with some fantastic video captured with some innovative use of a Go-Pro and a selfie-stick:


Larry writes: “Work at the start of this fiscal year focused on identifying any den boxes that were being used by fishers for reproductive purposes. We monitored all den boxes on a monthly basis by inspecting the inside of each box with a Go-Pro camera inserted through the door. In addition, hair-snaggers installed at the entrance of each box are examined and these were collected when any hair was present. Den boxes that were receiving attention by fishers also had motion detection cameras positioned to capture video of any fisher using the structure.

DNA samples from the winter of 2016-17 and the 2017 denning period were submitted for analysis in July 2017. Results of the analysis indicate 26 fisher samples were obtained out of the 39 samples submitted. Other species in the samples included red squirrel (8), American marten, (4), and one black bear. Of the fisher samples, we had 9 different individuals leave DNA at the denboxes (7F and 2M) during this period. Similar to the last two years, the denboxes appear to be selective for females. Out of the 9 fishers, 5 were individuals not previously identified.

During the reproductive denning period (April – June 2017), we observed females and kits at 4 different den boxes over the natal denning season. Three of the boxes used were in the Bridge Watershed and one was in the Chilcotin. The females had 1 at 2 denboxes and 2 at the remaining 2 denboxes. One of the fishers has used reproductive dens for three consecutive years at two different den boxes and a second has reproduced the past two years using two different denboxes.

A cannibalism event was also recorded on video at one denbox. A female with two kits had left to forage for several hours when a male fisher arrived at the structure. The male chewed at the opening to the denbox and, over approximately 0.5 hours, enlarged it sufficiently to enter the structure. The male was then observed to remove one kit at a time from the structure with one eaten on top of the denbox. Female fishers are selective for denbox entrance size, in theory, to prevent the larger males from entering and killing kits. However, to my knowledge, no one has recorded an actual cannibalism event. The female returned to the denbox that day and several other times over the next week.

Many of the denboxes have had the entrances enlarged by squirrel chewing over the years of the project and I suspect that this prior chewing may have aided the male fisher in entering the denbox. To address this problem, we have installed 2cm thick by 4cm wide door frames made from solid wood on every denbox. Future monitoring will seek to determine if this addition helps address the problem of squirrel chewing at the entrance. Another possible fix would be to embed galvanized metal sheets at the entrance during construction. Two metal sheets could be waffered between the 3 plywood layers at the opening. Plans for the final report are to update denbox construction plans to reflect these changes.

Other work this year includes visiting known fisher den trees to determine the potential supply of natural denning structures. Some delays for this component of the project were caused by the wildfires and my evacuation this summer. However, we have also commenced with this portion of the project and have some limited data to report. Near the Williston Reservoir, 6 out of 10 cottonwood den trees were still standing roughly 20 years after discovery. In the Chilcotin, only 2 out of five den trees are still standing approximately 10 years after they were identified. For the cottonwood trees, advanced decay appears to be the primary cause of all fallen trees. In the Chilcotin, recent fire has taken two trees and advanced decay impacted the third. There are 10 additional trees we plan to examine in the Chilcotin this winter and a biologist in the Peace has information on fisher den trees in that area that will help support this portion of the project.

Winter monitoring will commence in January 2018, when the boxes will be examined for chewing since last June. All den boxes will have lure added to attract fishers to the structure with trail cameras and hair snaggers used to monitor use over the winter. In late February / early March, we will move the cameras to den boxes that are receiving interest from fisher to prepare for the reproductive denning season.”

The artificial den box project is proudly supported by the Habitat Conservation Trust Foundation and the Forest Enhancement Society of BC.