Three winter surprises

An unusual bird, an unusual mammal, and midwinter construction

Regular bird-watchers spotted an unusual bird in Auke Bay this winter—an American coot. Although range maps show occasional migrants in southern Yukon, at the present time the Auke Bay record is the most northern, according to ebird. Coots are members of the rail family, which includes the sora that is often found in the Pioneer Marsh in summer. Most coots breed farther south of here, but there are isolated breeding populations in east-central Alaska and southern Yukon; this individual is presumably doing its winter things and may migrate north later.

American coot (cleaning up the harbor?) Photo by Kerry Howard

Although they sometimes use salt or brackish water on migration, coots typically nest in freshwater marshes with fairly deep water and lots of tall vegetation. They eat mostly aquatic vegetation, but also take small animals, both invertebrates and vertebrates, at times. Food is gathered by dipping the head underwater or by diving, and usually brought to the surface for swallowing. They sometimes feed on carrion, or steal from ducks, or even snatch flies out of the air. They are strong swimmers; they don’t have fully webbed feet but they have toes with lobes on the sides that increase the size of the foot paddle. 

Coots are strongly territorial, vigorously defending a nesting territory again other coots, as well as ducks, grebes, and sometimes other birds. They are socially monogamous, but in some populations there seem to be floater females that lack a mate and a territory and these females sometimes dump their eggs in the nest of a mated pair. Nests are placed on floating platforms of vegetation, often anchored on the sides by tall cattails and reeds. Multiple platforms are built by each pair and used for courtship, and one is used for the nest. The nest itself is made of small bits of vegetation, making a smooth basket big enough to hold the eggs, although this tends to get trampled flat by the time chicks are present. The floating platform tends to sink, so the parents have to continually repair and augment the structure.

A normal clutch size is about eight to twelve eggs per nest; larger clutches are probably due to the activities of egg-dumpers.However, most of the dumped eggs do not produce chicks, because the nest-owners usually reject the excess eggs. Both parents incubate the eggs, the males mostly at night. Incubation takes a little over three weeks, and the eggs hatch over a span of about three days. Chicks can hop out of the nest and swim around just a few hours after hatching, calling loudly for food to be delivered. Long ago, when I was doing my thesis research in the marshes of eastern Washington, I was fascinated by the goofy appearance of those little chicks, as they swam around after the parents. They have thick black down feathers with stiff, curly, orange tips, a nearly bald head, with some bluish patchesabove the eyes, that’s fringed with red or orange frizzy feathers, and a mostly red bill. It turns out that the oddball coloring is important in stimulating the parents to deliver food. Young birds are chased out of the parent’s territory after about three months, to live on their own and mature at age one year.

Also appearing this winter is another critter that is rare around here: Fishers live in northern forests across North America, but only recently (since the mid 1990s) have they been recorded in Alaska and southern Yukon. These pioneers are thought to arrive via the Taku River valley. Fishers belong to the weasel family (Mustelidae), smaller than wolverines but larger than marten. They climb well, because (like squirrels) they can rotate their hind feet so the toes point back; they are active year-round. Like other members of this family, they are fierce predators, capturing mostly rodents, hares, and grouse, but also eating carrion, insects, and fruit—but not usually fish, despite their name. Fishers are very good at killing porcupines, biting the face and then flipping them over to rip open the belly. They also sometimes prey on marten and weasels, and research has shown that these smaller mustelids tend to avoid times of peak foraging by fishers.

Fisher. Trailcam photo courtesy Riley Woodford

Although males and females mature at age one year, most successful breeding starts at age two. Dens for mothers and kits are usually in cavities in big logs and trees. Kits are generally born in early spring, and females come into estrus and mate a few days later. Sperm meets eggs and a fertilized zygote is formed, but it does not develop very much right away; instead, it just rests in the uterus until late winter, when it is implanted in the uterine wall and active development begins. Litter size is commonly two or three kits, weighing less than two ounces each, which depend on mother’s milk for at least three months and may be weaned at four months. By early fall, they are about full grown; males usually weigh about twice as much as females.

Trailcam photo courtesy Jos Bakker

One more little surprise: a trail cam in the Dredge Lakes area has recorded significant beaver activity in the middle of winter, despite heaps of snow and some very low temperatures. Small trees have been chopped down and hauled away, presumably for food. We seldom see winter activity like this around here. Adult beavers typically live on stored fat reserves while remaining in the lodge in winter. However, kits keep growing through the winter months, and they need to eat. They usually feed on a cache of sticks in front of the lodge, but maybe this family didn’t make a big enough cache.

Weasels of the forests

martens and fishers in Southeast Alaska

The weasel family is well-represented in Alaska; of the nine species here, three are associated with water and the others are chiefly terrestrial. Of the terrestrial species, marten and fisher are particularly associated with forested habitats.

Marten range over most of Alaska. There are two species of marten here: the American marten lives in the boreal forests across North America including most of Alaska; the Pacific marten lives on Admiralty and Kuiu islands (and maybe some other islands in Southeast). Marten are highly arboreal, spending lots of time in trees but catching much of their prey on the ground. Voles are a favorite prey in most places, but marten can capture prey the size of a marmot or a grouse. Versatile feeders, they also eat carrion and fruit. They have a slender build and an orange-ish patch of fur on the chest.

Fishers live across North American boreal forests but reach their western limit (for some reason) in the southern Yukon and adjacent mainland Southeast Alaska. This species probably originated in eastern North America and spread westward since the last glaciation (but there is said to be an ice-age fossil in central Alaska…). They occur at low densities here and in the Yukon, although there is some evidence that they may be increasing. Fishers are not only rare here but tend to be elusive as well, so sightings of them in the wild are few—and thus they get much less attention than other species. However, in the limited space of this essay, I choose to write more about fishers.

Fishers tend to be larger and burlier than marten, although small female fishers and large male marten may overlap in size. Male fishers commonly weigh 3.5-5.5 kg (some get much bigger!) and females about 2.0-2.6 kg. The fur is usually dark brown, darker than marten, but it sometimes has pale patches here and there. Like all the terrestrial weasels, fishers can climb well, even coming down a tree head-first, like a squirrel. That’s possible because they (like squirrels) can rotate their feet so the curved claws, when extended, hook into the tree trunk.

Both marten and fishers have short legs, so travelling in soft snow can be difficult. Fishers tend to travel less then, or often use existing trails (their own or those of hares). The foot-loading (i.e., body weight per area of foot) of fishers is greater than that of marten, and male fishers have higher foot-loading than females, so they may have a harder time in soft snow. Fishers, perhaps especially males, often leave body-drag marks in soft snow.

Kits are born in spring, often in a tree cavity. Litter size varies with the food supply: usually two or three kits but sometimes more or none at all. Females mate soon after birthing, although the embryo does not implant in the uterus wall until ten or eleven months later (late in the following winter). Gestation takes five or six weeks and the young kits are nursed by the mother for about ten weeks. All mammalian females spend a lot of energy on lactation; for female fishers, the cost of lactation plus the cost of extra hunting activity to fuel that milk production means that the total cost of reproduction is almost three times the energy needed during non-reproductive times. The kits are competent hunters at the age of four of five months, but most females don’t breed until they are two or three years old.

The home range size of fishers varies enormously, from just a few square kilometers to well over a hundred, apparently depending on prey availability. Males range more widely than females. Hares and small rodents are common prey in most places, but fishers also scavenge carcasses opportunistically and eat fruit and invertebrates at times. They can capture prey as big as a chicken or a porcupine; they subdue porcupines by attacking the vulnerable, quill-less nose until the victim is worn out.

The English common name “fisher” is a misnomer. Fishers may scavenge a few dead fish, but fish are not a common item on the menu. The name might come from a French word for the European polecat.