North American river otters (Lontra canadensis) can be found anywhere there is a permanent food supply and easy access to water, and are common in both fresh and coastal waterways across Massachusetts. Thanks to their well adapted body design, including webbed feet, a streamlined body, a thick muscular tail, and a dense coat of fur, otters are accomplished swimmers and underwater hunters. 

Small fish make up the bulk of a river otter’s diet throughout the year, but they will also consume crustaceans, mollusks and aquatic invertebrates when available. When fish does comprise a large percentage of an otter’s diet, their scat is often just a pile of fish scales and bones. Like owl pellets, researchers can use the prey remains in otter scat to reconstruct what species the otter has been eating. 

Interestingly, river otters are very particular about where they go to the bathroom. Otters tend to select a single location as a latrine, often on a prominent bank or large rock, and return to that same spot repeatedly. In fact, the photos included in this post were taken from a location with approximately a dozen relatively fresh droppings, indicating repeated use by one or more otters. Recent research has determined that these latrine sites may also serve a social purpose, as multiple otters often use a centralized latrine. Through scent marking activities involved with feces, urine and other secretions, otters can gather important information about other otters in their area from the scents that are left there. Such scent marking is crucial for intergroup communication.