Tag Archive | Weasel

Wisconsin’s Smallest Weasel Fosters Big Connections

The following piece was written by OAS Communications Assistant Claire VanValkenburg for the Snapshot Wisconsin newsletter. To subscribe to the newsletter, visit this link


Shifty colleagues, dishonest enemies and slimy adversaries are often referred to as “weasels,” but is this little mammal truly worthy of such a harsh reputation?

In truth, weasels are sprightly balls of energy and elusive hunters. The least weasel is both the smallest species of weasel in Wisconsin and the smallest carnivore in the world. It evades detection so well that they have been identified as a Species with Information Needs in the Wisconsin DNR’s Wildlife Action Plan.

According to Richard Staffen, Zoologist and Conservation Biologist at the Natural Heritage Conservation (NHC), we don’t know much about least weasels because they are not sought after as a furbearer. They are captured infrequently, and their small size exhibits low commercial fur value.

“There is little population data being collected, so not much is known on how they are doing,” Staffen says.

In an effort to bolster our understanding of the least weasel, Snapshot Wisconsin and the NHC have enlisted the help of a few University of Wisconsin-Madison students to tackle a collaborative classification project.

“You’d be surprised how well weasels can camouflage into their environment!” says Elizabeth Cleaveland, who recently completed a work-study position with the Wisconsin DNR as a graduate student with the Nelson Institute for Environmental Studies.

Cleaveland worked with Staffen last year to classify roughly 400 Snapshot Wisconsin triggers categorized as weasels by citizen scientists. Cleaveland’s successor is Mace Drumright, who says that while differentiating between species can be challenging, the work is important to better understand rare species like the least weasel.

“Weasels, and mustelids in general to a degree, have a tendency to escape notice and live relatively secretive lives, so any further insight into their behaviors and habitats is useful,” says Drumright.

Of the ~400 triggers students have worked to classify, Staffen says roughly 300 triggers are identifiable enough to assign a species. The least weasel shows up most infrequently on Snapshot cameras. Cleaveland recounts feeling surprised to see a least weasel on the Snapshot Wisconsin database, noting her excitement to learn that the species was still in the state.

“There are a couple of goals tied to this project, the first one being identifying small mammals in the area and the habitats they are utilizing. This is helpful in determining if the species is still present in the area, what types of habitat(s) they are utilizing, and if any wildlife management decisions need to be addressed,” Cleaveland says.

Drumright suspects that, other than martens, the least weasel could be the least photographed Mustelid species on Snapshot Wisconsin cameras.

“Hopefully this project will give better insight into the population and how they’re interacting with their environment,” says Drumright.

Staffen and the NHC are still working on analyzing the data to determine what percentage of the population the least weasel represents compared to other Mustelidae. But he says the information gathered from Snapshot Wisconsin data can be used in conjunction with trap data from Wisconsin fur trappers and small mammal surveys to make informed decisions on the species’ status.

“I think it is one useful tool, of only a couple, to assess the current population status of these infrequently encountered or under-reported species,” Staffen says.

Staffen and the Snapshot Wisconsin team hope to expand the collaboration, moving to chipmunk and squirrels next, which is another group of triggers that are not classified to the species-level.

“I just think it is a win-win project. The students really enjoy working on the project, they learn more about identification of these animals and their biology, we get some information on status and distribution and the Snapshot project gets a more refined classification.”

Keep an eye out for our shy woodland friend. Rather than impish, consider him tactful yet discrete. However you choose to view him, here at Snapshot Wisconsin we believe that while he may be little, he is not least.

Wily Weasels: The Math Behind Mustelid Identification

The following piece was written by OAS Communications Coordinator AnnaKathryn Kruger for the Snapshot Wisconsin newsletter. To subscribe to the newsletter, visit this link

Weasels are the most commonly misidentified animal in the entire Snapshot Wisconsin dataset. What might make them so tricky to identify, and just how do they differ from the other members of their family for whom they are often mistaken, like marten or mink?

As far as their phylogenic standing, weasels belong to the superfamily Musteloidea. Contained within Musteloidea are the families Mephitidae, which includes skunks; Mustelidae, including weasels, otters, ferrets and kin; and Procyonidae, with raccoons and their neotropical brethren. In examining the dataset of Snapshot Wisconsin photos that have received an expert classification, researchers have determined that weasels and mink are the two most difficult species for volunteers to classify.


The two avenues for classification available to volunteers through Snapshot Wisconsin are MySnapshot and Zooniverse. MySnapshot is the outlet available to those who monitor trail cameras, where they can classify the animals in the photos captured on their own camera. Zooniverse is a public forum where volunteers classify photos that are served up at random from Snapshot Wisconsin cameras across the state. Photos are captured in sets of three, called “triggers”, and volunteers classify the entire set at once.

recall_precision4When evaluating accuracy in classification, researchers focus on two variables: recall and precision. Both variables provide measures of accuracy for a group of volunteer classifiers, either from MySnapshot or Zooniverse, compared to expert classification. Recall addresses the question: out of all the weasel triggers in our dataset, how many did volunteers classify as weasels? Whereas precision addresses the question: how many triggers classified as weasels by volunteers were actually weasels?

Between both MySnapshot and Zooniverse, volunteers generally demonstrate high recall and precision when classifying animals that belong to the whole superfamily Musteloidea. When it comes to classifying individual species, we can see that animals like skunks, otters and raccoons are easier to classify correctly on account of their distinctive traits, but weasels are quite similar in physical appearance to the species with whom they share a family, namely mink. This makes weasels particularly easy to misidentify.

Triggers containing weasels and mink are most often missed completely on Zooniverse, with a recall value for these species of 41%. Out of an expertly classified sample size of 15 weasels, only 10 of the 15 were identified correctly by volunteers and 4 additional triggers classified as weasels on Zooniverse were not weasels. This puts recall and precision for weasel classification at a measly 67% and 71%, respectively.

For mink, Zooniverse and MySnapshot share low recall, with approximately 65% of mink photos missed completely on Zooniverse, and 39% missed on MySnapshot. However, the triggers that were classified were largely classified correctly, with perfect precision on Zooniverse and 87% precision on MySnapshot.

So how can we successfully identify a weasel versus some other mustelid, and vice versa? There are three types of weasels in Wisconsin. The long-tailed weasel is the largest of the three. They are typically 13-18 inches in length with a 4-6 inch black-tipped tail. Their coats are brown and their bellies and throats are cream-colored, though they transition completely to white in the winter. The short-tailed weasel is Wisconsin’s most common weasel. Smaller than the long-tailed weasel, the two share their coloring, which makes them more difficult to differentiate. The only discernible difference is the tail length. The third type of weasel is the least weasel, aptly named as it is the smallest of the three at roughly 6 inches. Though this weasel has coloring similar to the others, the least weasel has a short tail without the black tip.

Weasels look rather similar to mink, though mink are dark-colored and larger than weasels with long tails and glossy coats. They weigh between 1.5-2 lbs. Another mustelid closely resembling the weasel is the American pine marten, an endangered furbearer with a penchant for climbing. They have large rounded ears and a bushy tail, and their fur varies in shades of brown from almost yellow to almost black. Snapshot Wisconsin has only one confirmed photo of a marten, as the species is incredibly rare in Wisconsin.

Badgers seem like a no-brainer, with their characteristic striped heads and wide bodies. They are significantly larger than weasels and have long claws well-suited to digging. Despite their distinctive appearance, badgers are subject to misidentification as well. 22% of the triggers classified as badgers on MySnapshot were not badgers. The same goes for the fisher, another sizeable mustelid weighing in at an average of 15 pounds, with dark brown fur and a bushy tail.

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Classification is a tricky business, especially when it comes down to mustelids. Snapshot Wisconsin relies on thousands of volunteers to classify the nearly 34 million photos in our dataset, which they generally do with tremendous success. Though the weasel is a trickster, their phylogenic camouflage can be discerned with a trained eye – the same can be said for their Mustelidae cousins. Each accurately classified photo, mustelid or no, brings Snapshot Wisconsin closer to a complete representation of Wisconsin wildlife, and better informs our management of these species.

Snapshot Saturday: March 2nd, 2019

Can you spot the elusive Wisconsin native featured in this Snapshot Saturday? Hint: their winter coats make them experts at camouflage.

3.2.19 SnapshotSaturdayDid you know you can view and classify photos collected from Snapshot Wisconsin cameras across the state at www.SnapshotWisconsin.org? It’s a fun activity for the whole family!