life story
growth and reproduction
Both sexes are sexually mature at one year of age, but effective reproduction may not occur before two years of age. ospreys usually breed for the first time when they are one year old. females give birth in late March or April. after giving birth, females go into estrus and reproduce 7–10 days later.
both marten and fisher delay implantation. a fertilized zygote develops into a blastocyst and then becomes inactive in utero. the blastocyst remains inactive until late winter, when the change in day length induces implantation and active gestation. consequently, adult ospreys are pregnant most of the year, except for 7–10 days after delivery. Calving dates for anglers occur from late February to early May, but most litters are born from March to early April.
Litter sizes for anglers range from one to six, most commonly two and three. the young are called kits.
The marten and fisherman, like other mustelins, are altricial and are born completely helpless with their eyes and ears closed. they are partly covered with fine hair. kits begin to crawl at around three weeks; at three months, they go up. Fisher puppies are completely dependent on milk until they are 8 to 10 weeks old. a litter raised by her mother in captivity was weaned by her at approximately four months.
By 10-12 weeks, most kits are completely chocolate brown. during summer and early fall, young fishers have the same general color as adults, but are more uniformly colored. anglers weigh well less than 50 g (about 2 ounces) at birth, reach about 500 g (17 ounces) at 40–50 days, and thereafter begin to show sexual dimorphism in size. in late summer or early fall they approach adult size and sexual dimorphism is pronounced.
The fisherman and the marten exhibit intrasexual territoriality, allowing the ranges of a male and a female to overlap, although the animals may compete for the limited resources in their area of overlap.
Natal burrows used by mothers and newborn pups are often in cavities in large logs, snags, or living trees. maternal burrows are used by mothers and older, but still dependent young, and tend to be in less specialized structures, more like roosting sites, often high up in hollow trees.
Anglers have lived more than 10 years in captivity.
diet
The diets of the marten and angler are similar in that they both eat primarily rodents (Alaska-specific in parentheses: red squirrels, red-backed voles, long-tailed voles, and long-tailed mice), lagomorphs ( snowshoe hares), birds (black grouse), sometimes insects and carrion when available. individual studies suggest that they are opportunistic predators influenced by local abundance and availability of potential prey. Marten in southeast Alaska have been shown to prey on salmon, suggesting that salmon may act as an additional source of seasonal prey for anglers. the fisherman also feeds on his fellow mustelids: the stoat and the marten. Although the fisherman and marten eat a wide variety of foods, a few items tend to dominate.
The porcupine predator-prey system has been the subject of considerable study. fishermen are experts at killing porcupines and are one of the few animals that attack them. they bite into the face to injure and disable the animal, then turn it over and rip open its belly. the angler’s ability to climb trees headfirst is advantageous in attacking porcupines, which frequently climb trees when threatened. the fisherman can completely skin a porcupine, leaving the “coat of quills” in place of the kill, which is a sign of fisherman activity. fisherman often leaves the digestive tract without eating.
Studies correlating the number of commercially harvested fisher pelts and the 10-year cycle of hare abundance suggest that snowshoe hares are important. where snowshoe hares and porcupines are rare, anglers’ diets become more diverse and may include significant amounts of other mammals, reptiles, insects, and fungi. in some areas, fruits from shrubs and trees can make up as much as 30 percent of the summer diet. martens and anglers forage for carrion readily and are easily lured into traps, track plates, or camera stations that use meat as bait. Martens and fishers are active year-round, have demanding metabolisms, and, especially martens, store very little energy as fat.
