Mustelid diets

Mustelids are by definition carnivores, predominantly consuming meat. There are some exceptions to this rule who will opt for a side salad with their steak…but let’s be realistic, no mustelid will ever attempt Veganuary.

Mustelid dietary favourites range from rabbit (a specialty of the tiny stoat), to salmon (fish of the day for the otter), to earthworms (a badger favourite). While many of these mustelids have preferred food sources, there is some overlap in their diet in the UK¹ and, although mainly meat eaters, in times of limited food availability mustelids will scavenge, eating plant material and anything else that crosses their path. The mustelid approach to food is much like my labradors: if it smells edible, there will be a way to eat it.

Pine marten dentition

With their prominent canines and a penchant for furry creatures, pine martens fit the carnivore stereotype. They are biologically within the same Order (biological grouping) as bears (Ursidae), dogs (Canidae) and cats (Felidae)… amongst others. All carnivores possess a similar dentition with 4 sharp canines at the front, backed up with sharp premolars which include impressive carnassials teeth for cutting and shearing meat.

These teeth can tell us more about pine martens than merely what they eat. We can use teeth to age martens, most easily through looking at wear…with the sharper and whiter the teeth, the younger the animal.

Pine marten diet

Although known for their tree-dwelling lifestyle, martens do much of their hunting and foraging on the ground. In Scotland, pine marten diet is dominated by field voles…with some bank voles thrown in for good measure². In other regions, wood mice and yellow-necked mice dominate³. Alongside these small mammals, marten diet is then complemented by the seasonally abundant goods – like any good local restaurant. In Scotland this was found to be predominantly birds in summer and berries in autumn^2-4. In fact, in autumn, marten scat is often red and purple and filled with seeds from all of the berries available. Their attraction to sweet, tasty things is great for monitoring purposes – a tree smeared with some raspberry jam can help us collect really useful information about which martens are where. However, we discourage people from putting bait out to attract pine martens for fun. Not only does it put the animal at risk through disease transmission, but can draw martens into areas they would not normally be found, putting them in danger of predation or being hit on roads.

The diet of pine martens in Ireland differs from mainland UK because of the differing prey base. Ireland lacks the delicious field vole and studies have found Irish martens have more fruity tendencies, consuming a large amount of berries and insects^5,6. These food types are easy to detect in scat due to the undigestible nature of insect exoskeletons and seeds found in berries. Otherwise, marten scats are surprisingly hair-filled, with only a jaw bone or skull fragment of a vole allowing any straightforward prey identification. 

Martens tend not to dabble in aquatic prey, they leave this to the otters. However there have been a few anecdotal sightings of martens braving cold water to catch fish and birds⁷. Much of the media hype around pine martens in fact relates to their potential impact on squirrels. This may not be purely through direct predation but other mechanisms^8,9. However, pine martens are known to eat squirrels across their continental range. Winter diets in Russia and Scandinavia have shown up to almost 30% of marten diet comprised red squirrel^3,10,11, in Ireland, grey squirrel has comprised about 10% of marten diet in recent years¹². Evidence of squirrel consumption (particularly that of grey squirrel) is, however, limited. This is mainly due to the rarity of pine marten distribution overlapping that of the grey squirrel. We will be watching this field of research avidly in the coming years.

These larger prey items may be more challenging to catch but they do pay dividends. Martens sometimes cache these items, saving them for leaner times. Martens will sometimes cache (or hide) food in their den sites or in other safe locations and return for it at a later date¹³. This tends to be larger prey items such as squirrels as opposed to the bite-sized voles. In fact, we found the martens would stash eggs we left them inside den boxes in their release pens. Breakfast in bed?...yes please!

Foraging strategies and habitat

The flexitarian diet that pine martens demonstrate (academically known as facultative specialists) reminds us that martens are not bound to pine forest, or any forest at all for that matter. With their favourite prey in some locations being field voles, they need fields to forage in. In particular, long tussocky grass. Combined with fruit-bearing trees and insect-rich banks, these habitat mosaics are so important for martens, making up the perfect patchwork quilt for martens to exist in.

References

1. McDonald, R.A., 2002. Resource partitioning among British and Irish mustelids. Journal of Animal Ecology, 71(2)
2. Caryl, F.M., Raynor, R., Quine, C.P. and Park, K.J., 2012. The seasonal diet of British pine marten determined from genetically identified scats. Journal of Zoology, 288(4)
3. Zalewski A. 2005. Geographical and seasonal variation in food habits and prey size of european pine martens. Martens and Fishers (Martes) in Human-altered Environments. Springer, Boston, MA.
4. Jędrzejewski, W., Zalewski, A. and Jędrzejewska, B., 1993. Foraging by pine marten Martes marłeś in relation to food resources in Białowieża National Park, Poland. Acta Theriologica, 38(4)
5. Lynch, Á.B. and McCann, Y., 2007, August. The diet of the pine marten (Martes martes) in Killarney National Park. Biology and Environment: Proceedings of the Royal Irish Academy (pp. 67-76). Royal Irish Academy.
6. Twining, J.P., Montgomery, I., Fitzpatrick, V., Marks, N., Scantlebury, D.M. and Tosh, D.G., 2019. Seasonal, geographical, and habitat effects on the diet of a recovering predator population: the European pine marten (Martes martes) in Ireland. European Journal of Wildlife Research, 65(3)
7. Birks, J. 2017. Pine Martens. Whittet Books Ltd, Essex, UK.
8. McNicol, C.M., Bavin, D., Bearhop, S., Ferryman, M., Gill, R., Goodwin, C.E., MacPherson, J., Silk, M.J. and McDonald, R.A., 2020. Translocated native pine martens Martes martes alter short‐term space use by invasive non‐native grey squirrels Sciurus carolinensis. Journal of Applied Ecology.
9. Sheehy, E., Sutherland, C., O'Reilly, C. and Lambin, X., 2018. The enemy of my enemy is my friend: native pine marten recovery reverses the decline of the red squirrel by suppressing grey squirrel populations. Proceedings of the Royal Society B: Biological Sciences, 285(1874)
10. Sidorovich VE, Sidorovich AA, Krasko DA. 2010. Effect of felling on red fox (Vulpes vulpes) and pine marten (Martes martes) diets in transitional mixed forest in Belarus. Mammalian Biology 75:399–411.
11. Storch I. 1990. Diet and habitat selection of the pine marten in relation to competition with the red fox. Acta Theriologica 35
12. Sheehy, E., O’Meara, D.B., O’Reilly, C., Smart, A. and Lawton, C., 2014. A non-invasive approach to determining pine marten abundance and predation. European journal of wildlife research, 60(2)