In North Dakota marshlands, all dens were situated on shorelines and appeared to be in abandoned muskrat burrows. Active dens were not located where shorelines were heavily grazed. Mink are almost exclusively carnivorous. They are excellent swimmers and pursue both aquatic and terrestrial prey. Birds are important prey where fish and crayfish are scarce.
Mink tend to eat more fish in winter when fish are more accessible.
In autumn terrestrial mammals tend to increase in importance as prey. Mink mortality due to predators other than humans is not substantial. Development of shorelines that reduces structural diversity and removes snags and debris reduces mink activity. In Ontario residential development around lakes resulted in decreased mink activity due to loss of trees, decreased density of shrubs, reduction of aquatic snags, and removal of submergent and floating vegetation. Stream channelization has a negative impact on mink activity since suitable prey abundance is reduced when shallow, detritus-rich sloughs associated with meandering streams are replaced with abrupt, monotypic interfaces between aquatic and terrestrial cover types.