The eerie call of the Common loon (Gavia immer) can be heard echoing off of many lakes in Riding Mountain National Park. Loons have four different calls: tremolo, wail, yodel and hoot. Each call has its own purpose. You will often hear their tremolo as they fly overhead from distant nesting lakes to feed.
The park’s numerous clear water lakes are good habitat for loons as they are able to easily see their prey swimming beneath the water. Small fish are the most common source of food for loons, but if the water is murky or lacking small fish, they will feed on leeches, snails, and even insect larvae. Loons are great divers. They will often swim along slowly, sticking their heads into the water looking for fish, and then suddenly disappear below the surface without a splash. Loons are very fast swimmers underwater and will torpedo through the water to catch their prey.
Clear Lake is a popular feeding ground and it is not uncommon to see a group or raft of 50-80 individuals at a time on Clear Lake as they begin to stage in late July before migration in the fall. Groups get bigger as the mature and fledged young join the non-breeders on Clear Lake as summer goes on.
It is the male loon that will look for a suitable place to nest. Typically the chosen site will be in a quiet, protected, hidden spot on a lakeshore usually on islands or in bays. The nest is usually constructed of dead plant material like sedges and wetland grasses. Nesting pairs are monogamous and their pair bonds typically last five years. The average number of eggs laid (also known as clutch size) is 1-2 per season. If you look closely, you may see the loon chicks catching a ride on their mother’s back!
Overall, common loon populations in RMNP are healthy and stable. Because they require clear lakes, they are often considered an indicator of water pollution or an unhealthy body of water. Common threats to this species include mercury in the water, lead poisoning from fishing sinkers, human development, and recreational activities (i.e. motorboats).
For more information, visit the Cornell Lab for Ornithology at: https://www.allaboutbirds.org/guide/Common_Loon