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fisher in live trap.

FISHER (Martes pennanti)

Fisher are mammals in the Mustelid family. American marten, weasels, ferrets, mink, otters, wolverine, badger and 3 species of skunks are also included in this group. Mustelids have long, slender bodies and often exhibit sexual dimorphism where males are larger than females. Fisher were extirpated from most of their range in the 1920's and were reintroduced in many areas throughout the United States, including Wisconsin (1950's) and Upper Michigan (1990's). Fisher are opportunistic predators and research suggests they have a significant impact on the nesting success of northern goshawks and other woodland nesting raptors in northern Wisconsin because they eat the eggs, the nestlings and also the nesting adult females. Predation on adult females is extremely important because loss of these individuals can result in rapid declines in raptor populations.

The fisher in the photo is being trapped so a radio collar can be placed around its neck. As part of my thesis project I will collect data on the movements of the collared fishers and be able to estimate fisher home ranges as well as their habitat preferences during the spring and summer months, when raptors are nesting. I will also monitor active raptor nests in the Upper Peninsula of Michigan and identify the rate of mammalian predation, as well as the species responsible. This data may reveal the relationship between habitat overlap between woodland raptors and fisher during the breeding season and of fishers as the cause of increased predation rates of raptors. Alternatively, it may show that the majority of predation is caused by other mammals, such as American marten.

Contributed by Julie Gibson, a graduate student in UW Green Bay's program in Environmental Science & Policy.

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Last updated on April 15, 2014