At our Rock Ridge visit last week, I was sitting at our banding station when I heard some unfamiliar yelping coming from the north end of the lake. I couldn’t see anything at first, but as I peered through the trees toward the water I finally spotted some splashing. I thought ducks, initially, although the calls didn’t sound like ducks. It was only as the animals drew closer, moving south along the lake, that I could identify them: river otters!
Anticipating that their movement along the length of the lake would hopefully bring them near enough for a few distant photos, I grabbed up my camera and telephoto lens and was able to run off a few shots as they passed below me. It was difficult to count them as they splashed and dove, as they were rarely at the surface all at the same time, but I guessed there to be six individuals. They seemed to be diving underwater and resurfacing with food, although I couldn’t tell what it was they were eating.
Probably, though, they were catching fish, which make up the bulk of an otter’s diet. Otters are extremely well-adapted to life in the water, being streamlined with webbed toes and a strong tail that provide extra agility when hunting or playing. When I was out in the canoe on our previous visit I noted many smaller fish in the waters of Rock Lake, so there would be plenty to eat. Otters may supplement their diet with other small, aquatic animals such as frogs or crayfish.
Because of their aquatic lifestyle, otters have some unique adaptations. One of them is asymmetrical lungs. An otter’s left lung is nearly 20% larger than its right, and has four lobes compared to two for the right. This probably helps with how long the otter can hold its breath when it dives, increasing lung capacity and surface area for oxygen absorption. They can remain underwater for nearly 4 minutes, diving to depths of up to 20 meters (65 feet).
At this time of year, it’s most likely that they were a family group. In the early spring, after mating, the female sends her mate off for a bit of privacy while she gives birth to and does the initial raising of her litter. At about three months the kits are old enough that the mother begins teaching them to swim and hunt. The father rejoins the group once the young are about six months old, helping with their education. It seems a little early yet for the father to have joined the group, as six months ago means the young would have been born in February. Females may give birth to up to six young, so it may be she just had a large litter.
Otters are extremely social animals, an uncommon trait among mammals that live in our area. Mates spend half of the year together (the part when the young are grown), and family groups usually hunt and play together. Even adults aren’t opposed to a little fun, and may join the youngsters in games of tag or wrestling, or sliding down snowbanks or muddy embankments. They talk to each other constantly, and the entire time I watched them there was an ongoing dialogue of chirps and whistles.
The species is found through much of North America where lakes and streams are abundant, absent only from the drier Great Plains and arid southwest. Despite this, I’d never seen one before, so I was pretty excited by this encounter.
I apologize for the short absence; I was away for a couple of days and we’ve recently been having some technical difficulties with our internet that I hope will sort themselves out. I’ve had this post sitting since yesterday evening, waiting for our connection to come back online long enough to upload the photos and insert them into the post.