Is it a bird?...Is it a tree?...No, it’s a mustelid

Read the first blog by Cat, our Pine Marten Conservation Project Manager. She introduces you to the pine marten in Gloucestershire shortly after their reintroduction.

The pine marten is an elusive, quiet creature that many of us have never heard of. Yet these animals were once found all over the UK, part of our native fauna just like foxes, otters and badgers. So what exactly is a pine marten? Is it a bird? Like a house martin?... Is it a tree? Like a Scots pine?... No. It’s a mustelid! But what even is a mustelid?? I hear you cry. Well, let’s find out.


Mustelids are a family of mammals which include stoats, weasels, polecats, otters, badgers…to name the ones you may be familiar with in the UK 1. But this family has members world-wide. Including the bad-ass honey badger Mellivora capensis found in Africa and Asia. Its thick skin makes this guy tough and fearless as it searches for honey 2. Such a noble quest. However, the honey badger is not the biggest and the baddest of all the mustelids.

The mustelid family also boasts the membership of the wolverine. Yes, despite their bear-like appearance, wolverines are mustelids (not you Hugh Jackman, pipe down). This huge mustelid, around the size of a border collie with hair length to match, inhabits the northernmost part of the northern hemisphere 3. Its Latin name Gulo gulo translates as glutton, a result of its ‘enthusiastic’ eating style. I can relate. And, like most mustelids, the wolverine has a hugely varied diet. BUT it is still not the largest member of the family.

Weighing in at up to 45kg, the sea otter (Enhydra lutris) is largest of all the mustelids. This tool-using, paw-holding, kelp-anchoring fluff machine represents the mustelid family primarily on the west coast of North America 4.

Wolverine NA

Wolverine © Susanne Nilsson

But, let us not forget the small. The common weasel Mustela nivalis, brings up the rear when it comes to size. Nevertheless, what they lack in size, they make up for in tenacity (throwback to their demonizing role in Wind and the Willows). Distributed across the northern hemisphere, weasels feed primarily on small rodents, their narrow, tube-like body (a true mustelid trait) enables them to enter tunnels in which their prey normally find sanctuary 5. You go tiny floof!

So, although mustelids host this huge variety in appearance and body size, they do share some commonalities. In the grand scheme of things they are small, with elongated bodies, short legs and thick fur. If you were going to make one Blue Peter style, you would need a kitchen roll tube, 4 small rectangles of strong cardboard, a pipe cleaner, some brown felt…and an adult with a pair of scissors. Although, you could probably make half of Tracy Island with these items too. I digress, back to the mustelids. They all have distinct stink, with most having strong-smelling anal scent secretions 6. Most mustelids also have delayed implantation of embryos, known as embryonic diapause, allowing females to have young when conditions are favourable…they love a spring baby 7. And although omnivorous to an extent, mustelids do all share a similar dentition, with carnassial teeth specialized for eating flesh. In short, these are small tube-floofs not to be messed with.


Within the mustelid family sits the genus Martes (genus basically means group of animals with similar characteristics). There is a grand total of eight marten species, and just like the Hateful Eight, these martens all come from different places, each with a different back-story. There is representation from south-east Asia, to North America. Each marten species possesses highly similar physical features, but there has been artistic licence in their colour schemes. From the dip-dyed blonde that is the yellow-throated marten, the luxurious almost-black of the sable, the unfortunate yellow of the Japanese marten, to the classic cappuccino colours of the European pine marten, these species demonstrate great variety8. Unfortunately, this beauty has also been their demise and martens were, and still are in some countries, a popular part of the fur trade, with their pelts providing great warmth. Martens stand apart from other mustelids due to their ability to climb well, a result of their semi-retractable claws. Only meeting to breed, they are also solitary creatures. However, I still find it wonderfully warming that the collective noun for martens is a ‘richness’.

Yellow throat marten

Yellow-throated marten © Rushenb

Pine martens

Now that we are familiar with mustelids and martens, we should probably home in on the main event. The pine marten, the European pine marten to be exact; Martes martes. Up to 76cm nose to tail-tip and weighing in at around1.5-2kg9, these fuzzy beasts are native to the UK and Europe. Their name indicates an association with forested habitats, although do not be misled, pine martens are not limited to the trees and can thrive in scrubby areas too. Pine martens will regularly hunt in long, rank grassland and scrub to find their favourite food source, the field vole. Ironic really for a species that is an arboreal specialist. Their UK population has declined substantially in the 18-1900’s and martens are now a protected species in the UK. The Gloucestershire Wildlife Trust Pine Marten Project is playing a role in its recovery. Each month we hope to bring you a blog about pine martens in a hope that when pine martens are once again a familiar sight in the English countryside you will be fully armed with a wealth of pub quiz knowledge about these furry tree-floofs.

Pine marten

Pine marten © Terry Whittaker/2020 Vision

Until next time

Cat McNicol

Team Pine Marten


At Gloucestershire Wildlife Trust we are championing evidence-based conservation. So, just to confirm that none of this blog is made up, here is the true wisdom behind the words.

  1. McDonald, R.A., 2002. Resource partitioning among British and Irish mustelids. Journal of Animal Ecology71(2).
  2. Carter, S., du Plessis, T., Chwalibog, A., & Sawosz, E. 2017. The Honey Badger in South Africa: Biology and Conservation. International Journal of Avian & Wildlife Biology, 2(2).
  3. Copeland, J.P., et al., 2010. The bioclimatic envelope of the wolverine (Gulo gulo): do climatic constraints limit its geographic distribution?. Canadian Journal of Zoology, 88(3).
  4. Riedman M.L., Estes J.A. 1988. A Review of the History, Distribution and Foraging Ecology of Sea Otters. In: VanBlaricom G.R., Estes J.A. (Eds) The Community Ecology of Sea Otters. Ecological Studies (Analysis and Synthesis), Vol 65. Springer, Berlin, Heidelberg.
  5. Ylönen, H., Sundell, J., Tiilikainen, R., Eccard, J.A. and Horne, T., 2003. Weasels’(Mustela nivalis nivalis) preference for olfactory cues of the vole (Clethrionomys glareolus). Ecology, 84(6).
  6. Hutchings, M.R. and White, P.C., 2000. Mustelid scent‐marking in managed ecosystems: implications for population management. Mammal Review, 30(3‐4).
  7. Lopes, F., Desmarais, J., and Murphy, B. 2004. Embryonic diapause and its regulation. Reproduction, 128(6).
  8. Proulx, G. et al., 2005. World distribution and status of the genus Martes in 2000. In: Martens and fishers (Martes) in human-altered environments (pp. 21-76). Springer, Boston, MA.
  9. Birks, J. 2017. Pine Martens. Whittet Books Ltd, Essex, UK.