Loon or diver

Loons are spread throughout North America, Greenland, Iceland, and Eurasia. The five loon species are also called divers because of their excellent diving and swimming skills. Loons can swim underwater for hundreds of feet (several hundred meters) and may go to depths of 265 feet (80 meters).

Kingdom: Animalia

Phylum: Chordata

Class: Aves

Order: Gaviiformes

Family: Gaviidae

Genus: Gavia

Species: Various (see below)

The five loon species are famous for the sounds that they make. It is common to hear the tremolos, yodels, wails, clucks, mews, and cackles of loons around lakes and along the sea or ocean coasts. The long, slender bodies and sleek, graceful heads of loons help identify these birds as they fly and swim. A swimming loon may disappear in a dive and surprisingly reappear some distance away. They can dive to depths of 265 feet (80 meters) but usually swim around 33 feet (10 meters) deep. With webbed feet, they can swim several hundred feet (meters) underwater. Dives may last for several minutes but are usually less than one minute. Loons can adjust how low in the water they swim or how deep they dive by the position of their feathers. They change the amount of air in special air sacs and lungs so they float higher or lower in the water. Only penguins swim better than loons. Loons can not walk well on land, so they build nests near the water. Some nests are so close to or low in the water that they appear to float on top of the water. Loons usually nest away from the main shore and build nests on islands, islets, logs, or rocks that poke out of the water.

Loons are large birds that reach two to three feet (60 to 90 centimeters) long and weigh 2 to 14 pounds (1 to 6 1/2 kilograms). Females are smaller than males. The common (Gavia immer), yellow-billed (Gavia adamsii), Pacific (Gavia pacifica), and Arctic loons (Gavia arctica) have black plumage (feathering) with white spots on their backs and wings. The red-throated loon (Gavia stellata) is grayish brown with small light-colored spots and dark red throat patches. All loons have white underparts. Each species has vertical (up and down) white stripes on their necks. The stripes are in different patterns in each species. In the winter adults and young loons have gray feathers with lighter markings.

These aquatic (water) birds have excellent vision for catching their food. They catch crosswise in their beaks fish which are usually up to seven inches (15 centimeters) long. Some loons may catch fish up to 16 inches (40 centimeters) long. Loons also eat crayfish, shrimp, leeches, and frogs. Like other birds, loons have organs called gizzards. Pea-sized stones in their gizzards help them to grind and digest their food.

Loons do not likely face much danger from other predators. Loons either fly away or flee underwater if another animal frightens them or tries to attack. They may be threatened by water levels changing too much or too quickly. When this happens a disease called botulism can occur in the environment. A drop in water levels may allow tiny organisms called bacteria to live in and infect the decaying or dead plants and animals. This happens more quickly and easily in saltwater habitats than in freshwater ones. Hot weather and shallow, stagnant water cause the bacteria to grow faster. The result is that the loons get a form of food poisoning called botulism and die. Water plants that grow too much and hinder their swimming and diving are also a problem. The greatest threats to loons are environmental changes caused by humans. Acid rain, oil spills, and other forms of pollution all harm or destroy the habitats of loons.

A male and female loon build their nest together. The female usually lays two medium to dark brown or olive eggs with black spots or patches. The eggs of the common and yellow-billed loons are around 3 1/2 inches (nine centimeters) long and 2 inches (five centimeters) wide and weigh between four and six ounces (120 to 170 grams). The eggs of red-throated loons are slightly smaller. Both parents take turns incubating the eggs for 24 to 29 days. Incubation is when the parents keep the eggs warm so that they will hatch. The chicks have thick, dark gray to black down above and white on their underparts. Both parents care for the chicks (baby loons) and feed them insects and small invertebrates (animals without skeletons) which the parents catch fresh. Some bird parents chew and swallow food which they bring back to their mouths to give to their young. Loons do not do this. The chicks can leave the nest within one day of hatching and dive into the water. When very young, they can waddle upright for several hundred feet (meters) across the ground. Soon, though, they become better swimmers and divers like their parents. They can care for themselves after 8 to 11 weeks.

In the summer, loons live on lakes in the forest, taiga, and tundra regions of the northern hemisphere. During the winter most loons migrate to sea and ocean coasts. Some migrate farther south in their territories to live on large lakes without ice. Loons return to the same territories and nests most years. A pair usually nests alone and defends its territory around its nest. Arctic and red-throated loons may nest in colonies. Adult loons not breeding may form groups of 4 to 12 members in the summer. Loons may gather in groups of 80 to 250 on large lakes.

See the other essays about the four species of loons for further information.

Bibliography

"Common Loon." National Audubon Society, www.audubon.org/field-guide/bird/common-loon. Accessed 1 May 2024.

Winkler, D. W., et al. "Loons (Gaviidae)." Birds of the World, Cornell Lab of Ornithology, 2020, birdsoftheworld.org/bow/species/gaviid1/cur/species#genusGavia. Accessed 1 May 2024.