California’s Rarest: The Humboldt Marten

Anyone familiar with the montane fir forests of the Rockies or Sierra Nevada is probably familiar with the American Marten, a fast, agile, cat-sized weasel with a knack for catching chipmunks and squirrels. Well, it’s a little-known fact that the rainy forests of California’s Northwest – a globally-important biodiversity hotspot and one of my favorite regions of the state to explore – is home to a Marten subspecies of its own, the Humboldt Marten (Martes americana humboldtensis).

The cute, rare denizen of California’s coastal temperate rainforest used to occur along the coast from Fort Ross, Sonoma County, up to the Oregon border. However, this subspecies, unlike some other Martens, if very specific in its habitat preferences: they are practically restricted to old growth Redwood or Douglas-fir forest with a dense understory and sufficient snags. Sadly, this habitat has been largely destroyed in Northwest California, with the remaining habitat fragmented and localized to specific small areas, with very little connectivity between the remaining old-growth stands. Large-scale trapping campaigns in the 1950s practically sealed the deal. Not recorded for 50 years, they were feared extinct until USFS scientist Keith Slauson found a small population clinging on in the remote forests of the Siskiyou Mountains at the Humboldt-Del Norte County border, north of the Klamath River.

The remaining habitat of California’s last Humboldt Martens is one of the state’s last untouched wildernesses, an extremely rugged jumble of steep, rocky, densely vegetated ridges, heavy timber, and wild, rocky creeks. Detections of today’s remaining martens are clustered around two main regions: the old growth forests along the headwaters of Blue and Bluff Creeks, and the fog-laden serpentine pine forests of Red Mountain. This is perhaps one thing that makes the Humboldt Marten so unique – it’s ability to cling on in two vastly different habitats: densely vegetated old growth Douglas Fir and rocky, sparsely wooded maritime serpentine forest of Lodgepole Pine and Western White Pine on coastal ridges. However, even in the marten’s last bastion, all is not well. Between 2001-2 and 2007-8, a significant decline in the marten’s population (about 40%) was recorded, with significantly larger impact in the serpentine woodlands. Research into the Humboldt Marten’s habitat preferences indicate that increased logging in the Old Growth forests has pushed them into the maritime serpentine, less than optimal habitat by Marten standards. But they’re still clinging on here, stably breeding and feeding on Chipmunks and Golden-mantled Ground Squirrels in the rocky outcrops among dense manzanita, scrub oak, and ceanothus, a bit of a change from the Douglas Squirrels, Tree voles, and Cleithrionomys of the old growth.

To make matters worse, the USFWS rejected a proposal to list the Humboldt Marten as a threatened DPS (Distinct Population segment) due to its close relationship with martens in Oregon, also uncommon.

But when it comes this marten, it’s not all bad news. Recently, Martens were documented to have moved into Prairie Creek Redwoods SP. How they got there, nobody exactly knows – as Prairie Creek, south of the Klamath, is pretty far from the known habitat of the marten to the north. Further, substandard second-growth habitat connects the two regions for the most part. However, there was nonetheless cause for joy – as the Humboldt Marten’s survival or recolonization in Prairie Creek represents the first records of this mammal in the redwood zone in more than 50 years! Perhaps one day, we might see martens bounding through the redwoods once again in California’s parks, a once-small population having expanded well beyond the sheltering ridges and forests of its present home. We can all hope…