Naturalist Fact: American Mink

American Mink  (Neovison vison)

American Mink

The American mink is a fascinating voracious predator in the Mustelidae family, which includes otters, weasels, badgers, wolverines, and minks.  The Mustelidae family is actually the most diverse family within the order Carnivora.

American mink are an extremely widespread mammal found across North America, ranging from Alaska and Canada through the lower 48 states, with the exception of extremely dry areas of the Southwest.  The American mink has also been introduced to large portions of Europe where it is classified as an invasive species, linked with the decline of several native species including the European mink.   Although often difficult to view due to a secretive nature, the mink is quite common throughout much of its range.  In suitable habitat, populations may reach densities of 9-22 individuals per square mile.  Mink are considered semi-aquatic, and are rarely seen far from a water source such as streams, lakes, swamps, and marshes.  Occasionally mink can persist in dry environments if there is a steady food supply.  The majority of mink populations occur around fresh water, but coastal salt marsh also produces fine habitat for mink, with abundant prey.

Mink are strictly carnivorous, like all members of the Mustelidae family, and have a varied diet.  Typically the diet depends on the type of prey available, and small mammals such as muskrats and rats may be eaten more during the winter months.  Other prey choices can include ducks, seagulls, crustaceans, amphibians, and other waterfowl.  Being excellent swimmers, mink can swim up to 30 meters underwater and dive up to a depth of 5 meters in search of prey.  Mink are mostly active during the night.  An elusive nature combined with cryptic coloration help mink avoid predation, but occasionally they will fall prey to coyotes, bobcat, birds of prey, and snakes.

Male individuals are very territorial with each other, and have home ranges that may overlap with several female home ranges.  Breeding occurs during the winter months, and both females and males may mate with multiple individuals.  Gestation typically last from 45 to 75 days, and average litter size ranges from 1 to 8 kits are usually born in April or May.  Most kits become independent and find new territory from 6 to 10 months of age, and both male and females become sexually mature around 10 months of age.

The dense and fine pelage (fur) of mink makes it among the most important furs on the fur market.  Historically all pelts came from trapping wild populations which led to declines in populations, but most pelts in the fur trade are now produced on farms.  Wild populations have since recovered from the extensive wild trapping and are considered of least concern by the IUCN (International Union for Conservation of Nature).

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Black Skimmers nest on North Main Beach

Black Skimmers ward off possible threats to their colony.

We are nearing the end of the summer and the end of nesting season for our shorebirds. However, the Black Skimmers (Rynchops niger) have set up a pretty sizable colony on the northern tip of our beach, near Sancho Panza Creek. We estimate over 75 nests in the colony so far!

There are several beach-nesting birds that congregate in colonies including some gulls, terns, and the Black Skimmers. By laying nests at the same time in the same area, each nesting pair is reducing its chances of having their nest lost in the event that a predator comes in. Also, the Black Skimmers can become aggressive when defending their colony against outside threats.

However, if a predator like a raccoon (which frequent our beaches) were to discover the colony, they could wipe out the entire colony in just a few nights. This year, we are employing a new management strategy–electric fencing.

On June 21, we set up the first stretches of electric fencing around ten nests. With two separate areas fenced in, one was electrified and one was not. A few weeks later, the colony had expanded with nest “scrapes” spread over a much larger area.

Skimmer chick runs to its parent.

In mid July, we encompassed all of the scrapes and nests we had found with the electrified fence and haven’t seen any signs of predation by raccoons or other mammalian predators since.

 

The chicks and eggs are very well camouflaged!

 

 

Some of the earliest laid nests have begun to hatch, and there are several chicks running around within the colony. The chicks are still susceptible to predators, and as they start to move around we are worried they might venture outside the protection of the fence. After talking with members of our Ecological Advisory Board who suggested the chicks might move around in search of shade, we erected some temporary shade shelters within the colony.

Shade structures within the colony should prevent discourage chicks from leaving the fence.

We will continue to monitor the colony, and hopefully the Black Skimmers will continue their success!

 

 

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