Blog by Ed Snell – Project Support and Development at NatureSpy
Pine marten den boxes create a significant habitat enhancement by providing elevated, insulated resting and breeding dens. Den boxes are especially useful in areas where pine martens are recovering and the age structure or management of a forest means there’s less opportunities for natural denning sites, such as cavities in trees. Den boxes can be used year-round by pine martens, but we may expect to see some increased usage during colder months when a warm den is harder to come by, and during spring, when mothers are rearing kits.
VWT-style den box installation in Yorkshire
We’ve installed 46 pine marten den boxes in forests on the North York Moors as part of the Yorkshire Pine Marten Project. We use two different types of den box, both of which have proven to be successful over the past two decades with supporting Galloway Forest’s now well-established pine marten population. The VWT-style den box is the original design of the pine marten den box, featuring a central chamber that’s large enough for a female to raise kits in. The Galloway Lite den box is a smaller, lighter alternative to the VWT-style box, containing a smaller denning chamber. We use a combination of both types of boxes, creating a network of safe dens for pine martens across 11 forests on the North York Moors.
Our vision for pine marten conservation in Yorkshire is to help establish self-sustaining populations of pine martens as part of the national restoration of the species. Den boxes are a key part of this vision in helping pine marten populations to grow. With occasional maintenance, our den boxes in Yorkshire should endure the elements for 20-30 years. As the video above shows, these den boxes are already proving useful to our current, occasional records of pine martens in the region. In years to come, we anticipate there will be more pine martens in forests on the North York Moors as animals disperse from growing populations further north, along with potential translocation projects to help boost pine marten numbers in Yorkshire.
Galloway Lite den box in Yorkshire
In 2017, we captured the first ever camera trap footage of a pine marten in Yorkshire.
30 den boxes installed: 3 in 2019, 12 in 2020 and 15 in 2021. These boxes add to at least 13 that were installed by Forestry England, prior to the Yorkshire Pine Marten Project.
Pine marten recorded prospecting 2 den boxes, both of which were from our first 3 den box installs in 2019. Pine martens are curious yet cautious animals, this footage shows an animal exploring a den but choosing not to use it.
At this time we also recorded footage of a pine marten at nearby baited camera locations too. It appears that this footage and the den box footage is all the same animal from the unique bib fur markings.
A further 16 den boxes installed, taking us to a total of 46 den boxes now setup, providing a network of dens for pine martens on the east and west sides of the North York Moors.
Prospecting behaviour recorded at 4 den boxes and our first recorded footage of pine marten using a den box as a resting site in Yorkshire. The den box being actively used as a resting den was installed earlier in 2022 (see above video). Similarly to the previous year, other footage was recorded of this pine marten at nearby at baited camera locations too, although it appears to be a different animal to the previous year as it has a different bib fur pattern.
Footage of prospecting behaviour around den boxes in Yorkshire.
From our camera trap footage in Yorkshire, we’ve found that if a pine marten is roaming an area and discovering our baited feeding stations, it has also found den boxes nearby within 1-3km of a baited feeding site. Although we cannot draw any conclusions based on the small amount of data we have, it does seem that pine martens have no trouble finding den boxes. High success rates with den box use have been recorded elsewhere; for example, den boxes that have been installed over the last 20 years in Galloway Forest have shown frequent signs of use by this now well-establish pine marten population.
Pine marten prospecting a potential den in Yorkshire
Den boxes have an added benefit of helping us to target our monitoring efforts in Yorkshire. Alongside our normal camera trap surveys, we monitor den boxes in a couple of different ways to gather records of pine marten activity, helping us to build an evidence base to inform pine marten conservation.
There are field signs to look out for that show possible den box use, such as pine marten scats on the top of a den box and claw marks and polishing on the branches below a box if it has been frequently used. These field signs, however, don’t indicate that a box is in use at that moment.
To find out if a den box is currently in use, we use thermal imaging scopes. This means that we can monitor den boxes from a distance, avoiding disturbance to any occupants, and get an immediate insight into whether a box is in use. If we see a thermal signal showing a box is in use, we then install a camera trap, again keeping a distance to avoid disturbance, to confirm if it is a pine marten inside and record any behaviours. In some instances, we’re able to identify individual animals if we can get clear footage of their bib fur pattern.
In the new year we will be publishing a guide for monitoring pine marten den boxes with camera traps, reflecting our experience with projects in Yorkshire and Galloway. If you’re looking to get set up with den box monitoring pre-emptively for the natal season from February 2023, please get in touch and we’ll send you an advance copy of the guidance.
Thermal scope image of a Galloway Lite den box with a pine marten inside in Galloway Forest.
All of our Yorkshire den boxes are installed in forests that are owned or managed by Forestry England. Den boxes are best suited to areas where natural denning opportunities are harder to come by. This is typically in younger, coniferous woodlands that provide fewer elevated denning opportunities. Mature broadleaf and coniferous woodlands naturally provide a better selection of denning sites for pine martens, so these areas are typically not suitable for den boxes as they shouldn’t be needed.
We work closely with Forestry England staff to identify den box locations that cover a variety of locations that are unlikely to be managed for several years or more. Potential locations are identified using maps, these sites are then visited to find an exact location, then the final location is confirmed before the den box is installed. When seeking a tree for a den box, we also consider which trees nearby will be suitable for a camera trap in the future, helping to make monitoring more straight forward. Carefully selecting den box locations in this way means that we are establishing a network of den boxes that can be used by pine martens for many years to come. Should an unlikely case arise where a den box needs to be moved, the box is monitored with camera traps in weeks prior and any work that may cause disturbance to denning pine martens is carried out by a licensed professional.
We’ll be keeping an eye on Yorkshire’s pine marten den boxes over the winter months and into spring. Check back to our News section for future updates!
Learn more about the Yorkshire Pine Marten Project on our project pages.
