This week in the woods, fisher tracks wove through mature mixed hardwoods, planted red pines, and hemlock stands, along downed logs, across streams, and over wooded hills. We followed the prints for miles but never caught up to the secretive members of the weasel family. Their energy-efficient lope can take them well over a dozen miles in a day, especially when the snow is not deep and powdery, and their home ranges can reach up to 40 square miles.
Males travel especially far when seeking mates between February and April, and we saw evidence of a pursuit – two sets of tracks and numerous stumps turned into scent stations with feces and urine. Fishers mount these protrusions from the snow and rub and roll themselves on them. Once members of a pair find one another and copulate, the male departs, on to the next encounter. Meanwhile, if sperm meets egg, the embryo does not implant in the uterine wall until ten or eleven months later. This remarkable process, called delayed implantation, spares the female the energy cost of growing an embryo and allows the kits to enter the world in springtime, just as the northern forest begins to offer up more food resources.
Regardless of time of year, porcupines fall prey to fishers – one of only a few animals, along with coyotes and great horned owls, known to hunt them with regular success and an essential component of controlling their populations. (We found these porcupine remains buried partially in the snow beside the fisher tracks.) Depending which scientist you ask, fishers either force the quillpigs out of trees to their deaths or attack their vulnerable faces until they succumb and show their soft bellies.
Another prickly thing a fisher seems to have eaten the meat out of, a beechnut husk along the trail reminded us that these animals are omnivorous. Beaked hazelnut, apples, blackberries, and blueberries all factor into their diet, alongside squirrels, reptiles, amphibians, birds, and bird eggs.
Over a stream the fishers crossed, these pendulous ice formations developed. The running water splashed and met an overhang, the spray turned to ice in the freezing air, and the liquid below continued to smooth and shape the surfaces of the structures.
Elsewhere in the woods, other signs of the spring melt showed. The bases of trees displayed thaw circles – rings where snow in contact with the dark, heat-absorptive bark has melted faster than the reflective snow around it. Spring ephemerals sometimes take advantage of these gaps to gain earlier access to sunlight.
These areas of early melt provide a cross-section of the subnivean zone and reveal rodent tunnels that have run beneath the snow through the winter. The winter microhabitat of shrews, mice, and voles, the subnivean zone takes its name from the Latin words for “under” (sub) and “snow” (nives). It forms when solid snow warmed by the ground sublimates and the resulting water vapor moves through the snowpack to the surface, which it changes into small, tightly packed, rounded ice particles that seal in heat. The snow caves maintain relatively stable temperatures (around freezing) and humidity, with heat released from conversions between ice and liquid water. Small creatures remain protected from sub-freezing temperatures and wind, get access to seeds, groundcover plants, bark at tree bases, and insect eggs, and stay hidden from predators.
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