A Year in the Life of a Pine Marten

Pine martens are among the UK's most elusive mammals. Their secretive nature has long fascinated both members of the public and scientific researchers. In this blog, we explore the captivating life of a pine marten throughout the year. We'll look closer at how they adapt to the changing seasons, key moments in the development of kits, important food resources, and the value of safe, cosy dens.

"Two dots" - Photo by Paul Willoughby

Spring - New Arrivals & Adapting for Summer

From March onwards, litters of 1-3 pine marten kits are born within the safety of a den. The preferred locations for such dens are usually pre-existing cavities in older trees, offering a secure, elevated space above ground for the kits to grow. The kits are born blind and fully dependent on their mother and will remain in their natal den for around six weeks.

Throughout the year, the pine marten’s diet primarily consists of small mammals, fruit and birds, with the balance shifting depending on the season and location. Small mammals are particularly important in spring, with the short-tailed field vole (Microtus agrestis) alone accounting for 36% of the diet according to a study in Scotland. In Northern England, where our own Yorkshire Pine Marten Pathways Project is based, wood mice (Apodemus sylvaticus) appear to fill this dietary niche.

During spring and summer, when young grey squirrels are abundant, they are also included in the pine marten’s diet. The relationship between pine martens and grey squirrels is a focus of ongoing research, with promising implications for red squirrel conservation.

The pine marten’s physical appearance also transforms with the changing seasons. As temperatures rise, they shed their thick winter pelage in favour of a sleeker, thinner coat. The new coat is a deep chocolatey brown, with any markings appearing clearly on their distinctive creamy yellow bib.

Summer - Breeding Season & Boisterous Kits

The young kits born earlier in the year are now strong enough to begin venturing out of the den. The abundance of food during the summer months provides the perfect conditions for them to learn essential hunting and foraging skills from their mother.

In the summer, pine martens maintain an opportunistic diet, but with a higher proportion of birds compared to earlier in the year. While small mammals remain part of their diet, small birds become a more significant food source, especially in June and July. In a Scottish study, birds accounted for 38% of their diet during this period.

Despite being typically solitary and territorial, adult pine martens come together in the summer for the breeding season. Their pregnancies will not officially begin until later in winter due to a reproductive strategy known as delayed implantation, which is observed in several carnivore species.

Although pine martens are commonly considered nocturnal, they are also active during daylight hours, albeit less frequently. A radio-tracking study in Białowieża National Park revealed that 31% of their activity occurred during the day. With the longer, brighter summer days, there may be a better chance of spotting a pine marten on the move.

Exciting camera trap footage of a pine marten active in daylight hours.

Autumn - Adapting for Winter

By autumn, at around six months old, this year's kits are fully grown and independent. Despite this, they will generally continue to stay within their mothers' territory until later in the winter.

Seasonal fruits such as rowan berries and blueberries ripen and become an important staple in the pine marten’s diet. Research has found plant material contributes over 50% to their autumnal diet. This is the key time for them to feed up in preparation for higher levels of denning during the chillier winter months.

As the colder weather approaches, the martens develop a thicker, paler winter coat. This change gives them a distinctly 'fluffier' appearance, which is crucial for insulating them against the dropping temperatures. Their tails become increasingly thick and bushy.

Winter - When Cosy Dens are a Priority

In late winter, nearly a year after their birth, the young adults disperse to establish their own home territories. The young martens will wait until they are 2-3 years old before they breed.

Like other mustelid species in the UK, pine martens do not hibernate. Instead, they remain active throughout the winter albeit at significantly lower levels. Daily activity drops from around 13 hours per day in summer, to only 2.5 hours a day in the winter months.

Outside of these rather limited active hours, the pine martens will seek out cosy dens. Throughout the winter, they spend significant time in these dens, which provide shelter from harsh weather and cold temperatures. In areas with limited natural den sites, they may seek out alternatives such as buildings or artificial den boxes, such as those we have installed in Yorkshire.

Camera trap footage of a pine marten exploring several den boxes on the North York Moors.

As winter draws to a close, the fertilised eggs from the previous year implant in the uterus, and fetal development begins. This pregnancy will last a month, timed to give birth around March to April, ensuring the kits are born when food is more plentiful and the colder months are mostly avoided.

As the seasons shift back to spring, the pine marten’s yearly cycle begins again.

The camera trap images and footage in this article was captured by the North East Yorkshire Pine Marten Pathways Project. The NE Yorkshire Pine Marten Pathways Project is a partnership of Forestry England, NatureSpy and Yorkshire Wildlife Trust. The project aims to set the future direction for pine marten recovery in Yorkshire. Learn more about the project here.