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Last updated: 23 January 2023
An aquatic bird that is far more at home on water than on land, loons are a common sight on lakes across Canada and Alaska where they head to breed each spring.
Keep reading to learn more about the sites they choose and other nesting habits of these sleek diving underwater hunters.
Loons, known as divers in the UK, are not well equipped for walking long distances on land, and build their nests close to the water’s edge, either on islands or in waterside patches of vegetation.
To find out more about how loons select nest sites, construct nests and raise their young, keep reading as our complete guide to loon nesting habits will look at these topics in depth.
Close up of a Common Loon sat on the nest - known as Divers in the UK
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Loons are not adept at moving on dry land and spend as little time out of the water as they can manage. Mating occurs on land, but the species is far more at home on the edges of lakes or ponds, or around the shores of small islands where they stand less chance of being disturbed or predated.
Nests are built surrounded by water, using underwater vegetation as a framework on which to build around.
If flooding is a risk, then it’s common to see an extra large nest construction, which has been built up to raise the height above the surrounding water levels.
Finding a nest site is the responsibility of a male loon, and it is common for males to return to sites they have successfully bred in in previous seasons to establish a new nest with either the same mate or a new partner each year.
Close up of a nesting Common Loon
It’s highly unlikely that a loon pair will set up home in a backyard, unless that yard backs onto a lake and offers secluded, undisturbed areas in which a suitable nest could be built.
Loons spend as little time as possible on dry land, and even nest sites are constructed in spots that are either surrounded by water or on raised vegetation beds under shelter on a lake’s edge.
Loons prefer to build their own bulky nest platform, using wet leaves, moss, mud, and decaying plant matter they bring to the surface from the bed of the lake they are nesting on or near.
On rare occasions, an egg may be laid on a rock, without any surrounding structure in place, but this is not common.
Nesting platform of a Loon, with two unhatched eggs in the nest
Loon nests are bulky platforms made from wet leaves and other decaying plant matter dredged up from the bottoms of lakes and ponds, and crafted into shape by both birds using their bodies to make a shallow inner depression on which the eggs are laid. No lining is added and the eggs remain uncovered at times when the nest is briefly left unattended.
Not a lot of data exists about the exact measurements of loon nests, but from observations of nest sites in Minnesota, the following dimensions have been noted – inner diameter, 24.4 to 33 cm (9.6 to 13 in), outer diameter 55.9 to 56.9 cm (22 to 22.4 in). Loon nests are bulky structures, and can weigh up to 18 kg (40 lb).
Common Loon close-up view nesting on its nest and turning brood eggs in its environment and habitat
Nesting begins from April onwards after males arrive back on their breeding territories from their wintering grounds.
Female Loons arrive some days or weeks later, not always to their previous mate, and pairs form again, with some weeks taken to create or refresh a strong bond before nest construction begins.
It takes around four weeks of brooding for loon eggs to be able to hatch successfully, with 26 to 30 days being noted as the upper and lower ends of the range.
On hatching, young are able to leave the nest within hours, sometimes carried on their parents’ backs for their initial forays across the water.
Close up of a Common Loon on the nest with two eggs on Wilson Lake, Que, Canada
The most common laying period for breeding loons is between April and June, depending on geographical location. Some eggs, particularly when a second, replacement brood is attempted, will be laid into July, but any later into the summer is unusual.
Loons leave their breeding territories in winter when they become too cold to remain on. Frozen lakes are no good for loons, which spend much of their time hunting, or swimming on the water surface, due to their inability to survive well on land.
In winter, they head out to sea, where clearer waters provide better hunting opportunities and a chance for them to safely undergo their annual molt. During this time, they sleep when they can on open water, and do not build winter nests to rest on.
Common Loon undergoing the annual molt
The nest site is chosen by the male alone, who develops a strong attachment to his territory and will reuse it in future seasons.
Damp leaves and plant material are gathered from around the nest site, or carried to the water surface from the bed of the lake. This decaying matter is then arranged into a loose circular bed, either raised from the surrounding water or on the shoreline of a small island, a short distance from the water.
A shallow depression in the leafy structure is shaped by the birds, sitting on the nest and pulling materials together around them. Nest construction typically takes less than a week to complete.
Wet leaves, moss, and other sodden plant matter are shaped into a nest bed, and firmed up with other decaying plant matter from the bottom of the lake or reservoir.
On rare occasions, eggs may be laid in a shallow depression on the shore of a lake or island, or even on a bare rock.
Male loons initiate site selection early in the breeding season. Once construction starts, males and females work together to gather materials, throwing sludgy matter sideways onto the pile using their beaks to carry it into place.
Then they use their bodies to shape the materials they have gathered to form the nest bed.
Breeding pair of Common Loons with their chick
Loon eggs are olive green to brown with dark splodges. They measure around 8.9 cm (3.5 in) in length and are roughly 5.6 cm (2.2 in) across.
Loon clutches typically consist of two eggs, although on occasions only one egg may be laid. Eggs are laid between one and three days apart.
Male loons take turns with females to incubate eggs. Observations show that females take a larger share of overnight incubation duties and also brood for longer periods than males as the time to hatch approaches.
Close up of two Loon eggs in the nest
Baby loons are born in a precocial state - with feathers and ready to swim and forage almost immediately. For the first two weeks of their life, you may see young chicks hitching a ride on their parents’ backs as they are taught vital survival skills.
For the first six weeks, young loons are fed mainly by their parents but gradually master the art of diving for their own food. Once they reach 11 or 12 weeks, loons are able to catch almost all of their own food, and have also started to fly.
It’s most common for a loon pair to raise one single brood in a season. A rare second brood may be attempted, particularly if an earlier nest fails. For second broods, it is not uncommon for only one egg to be laid.
Baby Loon riding on the back of its parent
When a nest shows signs of failing, especially caused by predation or floods, loons will abandon their current nesting site and unhatched eggs and start again nearby.
Up to three attempts will be made to renest when an original nest is abandoned.
Loons’ nests are constructed as close to the ground as possible, and off-ground sites in tree branches will never be considered.
Sometimes a simple depression scraped in the ground will be enough of a nest, although more typically a bed of wet leaves on either the shore of a lake or watery location with underwater vegetation to build upwards on is the preferred style.
As loons are not compatible with walking on land, they are at less risk to predation if they sleep on water.
They nap during the day and night for short bursts of sleep, and although are not truly nocturnal, it is not unusual for the species to be active, hunting on their home pond or lake after dark.
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