What do hungry loons eat?
Fresh and saltwater fish are the primary diet of Common Loons. However, both adults and juveniles also regularly eat crustaceans, especially crayfish, and aquatic invertebrates. During the summer, adults eat many species of freshwater fish, including yellow perch, suckers, shiners, and occasionally small trout. In the winter, loons have a very different diet because they live in saltwater along the coast. Fish such as flounder and herring, as well as crustaceans, are regular components of their winter diet. Loons have a salt gland to excrete excess salt that they ingest while feeding on the ocean.
Loons typically eat fish weighing 10-70 grams. Adult birds, especially large adult males, occasionally catch large fish (up to 250-300 grams). A big fish, such as a full-grown sucker, can take a several minutes for a loon to subdue and swallow. The loon may drop the fish and dive after it repeatedly, stabbing at it again and again with its beak, until the fish is subdued and can be eaten. A large fish will cause a loon's neck to bulge out until the fish moves down into the stomach and is digested.
Loons are visual hunters, thus they need relatively clear water conditions to find prey. Adults prefer to hunt in shallow water, and eat whatever is easiest to catch and most abundant. Feeding dives are usually less than a minute, although if prey is hard to find, the dives can be longer. To help them digest fish bones and the shells of crustaceans, loons also ingest small pea-sized stones. An average of 10-20 stones are maintained in the gizzard, which grinds down the hard items to enable them to pass through the lower digestive tract easily.
Once a fish or other potential prey is located, the loon dives, holding its wings close to its body, and uses its powerful feet for propulsion while swimming underwater. The fish, crayfish, or other prey is captured in the loon’s bill, and with the exception of large fish, is consumed while still underwater. If the loon catches a large fish, it may release and catch the fish repeatedly until the fish is subdued, and the loon can swallow it whole.
Juvenile loons are fed fish appropriate to their size. Adults carry small minnows and sunfish, crayfish, and aquatic insects sideways in their bill to bring food to their chicks. The young birds often watch underwater as their parents are hunting, and begin trying to catch small prey when they are ~4-6 weeks old. By the time they are in the immature feathered plumage, juveniles are capable of catching and eating larger items, up to several inches in length. However, they will continue to beg for food incessantly from the parents until the late fall when the adults leave for the coast (probably because they get tired of the persistent begging of their chicks!), and the young birds are left on their birth lake to fend for themselves.