Pacific Loon

Males arrive on the breeding grounds first, selecting a nesting lake and establishing a territory they will defend for the entire season. Pairs are monogamous and typically mate for life, returning to the same breeding lake and often the same nest site year after year. The nest site is almost always at the water's edge — on a lakeshore, island, or islet — positioned so the birds can slide directly into the water if threatened. The male selects the site, with a strong preference for locations offering wide sightlines and easy water access.

Both sexes build the nest, arranging mud and dead aquatic vegetation into a basic oval mound. A land nest can be completed in a few hours; a floating nest takes a day or two. The nest bowl averages about 23 cm (9 inches) across and 2.5 cm (1 inch) deep. The female lays 1–2 eggs (rarely 3), coloured in variable shades of buff, brown, and olive-green with blackish-brown spots, measuring approximately 76 × 47 mm. Eggs are laid a few days apart but typically hatch within a day of each other.

Both sexes incubate, though the female takes the larger share. Incubation lasts 23–28 days. Chicks are downy and active at hatching, leaving the nest within 1–2 days. They can swim immediately but are vulnerable to cold and predation, and adults carry them on their backs for protection during the first weeks of life. Both parents feed the young, sometimes flying several kilometres from the nesting territory to bring back fish.

Chicks cannot fly until approximately 50–65 days old and become fully independent at around 57–64 days. One brood is raised per year. In the southern part of the range, breeding may begin as early as March; in the high Arctic, it depends entirely on the arrival of ice-free conditions. Timing of spring ice melt is therefore a critical factor in annual breeding success.

Pacific Loons are long-lived birds, with typical lifespans estimated at 15–25 years. Like other members of the Gaviidae family, they invest heavily in each breeding attempt — raising only one brood per year with both parents sharing incubation and chick-rearing duties — a life-history strategy that favours longevity over high reproductive output.

Adult survival rates are high once birds reach breeding age, and the species shows one of the highest territory retention rates recorded for any waterbird. Males are particularly tenacious, outperforming females in holding territories not because of size advantage but apparently due to fighting ability and experience. This fidelity to breeding sites means that long-lived individuals accumulate detailed knowledge of their nesting lakes, which likely contributes to improved breeding success over time.

The main sources of adult mortality include entanglement in commercial gill nets, oil spills and pollution in coastal wintering areas, harmful algal bloom events (a single 2007 bloom killed over 1,000 seabirds off the northwest Pacific coast), and mercury bioaccumulation, which can impair neurological function and reproductive success in long-lived fish-eating birds. Nest predation by foxes, ravens, and large gulls is the primary cause of breeding failure rather than adult mortality.

By comparison, the closely related Common Loon has a recorded maximum lifespan of around 30 years. Pacific Loons are likely capable of similar longevity, though confirmed long-lived individuals are less well documented due to the remote nature of their breeding grounds and the challenges of long-term banding studies in the high Arctic.

The Pacific Loon is listed as Least Concern on the IUCN Red List. The global population is estimated at 840,000–1,600,000 individuals, with Partners in Flight estimating around 840,000 breeding birds in North America alone. A recent study of the western Alaskan Arctic found the local population was approximately 1.5–2.0 times larger than previous aerial surveys had indicated, suggesting the true global total may be higher still. The species' range covers approximately 15,700,000 square kilometres, and the overall population trend is considered stable to increasing.

Despite this broadly positive picture, regional declines have been documented. Spring migration counts in California showed a sharp decline between 1979 and 1996, and Pacific Loons decreased approximately 3% annually in the Anchorage subregion during that period. The species scores 10 out of 20 on the Partners in Flight Continental Concern Score, indicating low but not negligible conservation concern.

Key threats include oil and gas development in the National Petroleum Reserve in Alaska and other tundra breeding grounds; mercury contamination from legacy mining and coal-fired power plants, which bioaccumulates up the food chain to loons; and harmful algal blooms in coastal wintering waters. A 2007 bloom off the northwest Pacific coast killed over 1,000 seabirds, including Pacific Loons. Additional threats include plastic ingestion, commercial gill-net bycatch, disturbance at nest sites (researcher disturbance during incubation measurably reduces egg survival), and climate change driving rising ocean temperatures and increased algal bloom frequency.

Pacific Loons are still hunted and their eggs gathered in some native Arctic communities, though the scale and population-level impact of this is not well quantified. Conservation efforts focus on protecting tundra breeding habitat, monitoring mercury levels in prey fish, and reducing bycatch mortality in commercial fisheries.

Courtship in the Pacific Loon is an elaborate, synchronised affair that reinforces the pair bond before and during each breeding season. The most characteristic display involves both members of a pair simultaneously dipping their bills into the water and then performing a rapid splash-dive — a behaviour that appears to function as a mutual assessment of fitness and coordination. Pairs also engage in synchronised swimming, moving in tight parallel formation with heads held low over the water.

Copulation takes place on dry land and is frequently repeated throughout the pre-laying period. The female initiates by climbing onto the lake edge, bowing her head, and raising her tail — a posture that signals receptivity. The male responds by mounting, and the pair may copulate multiple times in a single day.

A distinctive feature of Pacific Loon social behaviour is the group display, in which non-breeding birds — typically failed breeders or unpaired individuals — gather in small flocks late in the day on open water. These groups perform synchronised bill-dipping and diving, accompanied by vocalisation, in what appears to be a form of social bonding or mate-prospecting behaviour. These gatherings can involve up to a dozen or more birds and are most commonly observed in late summer, after the main breeding season has ended.

Territorial defence is vigorous. Males advertise ownership of a nesting lake with loud yodelling calls audible for several kilometres, and will physically confront intruding loons with an aggressive rush across the water surface, wings half-spread and neck extended. Fights between rival males can be prolonged and occasionally fatal.

Among the loon species, the Pacific Loon holds a particularly striking place in the cultural history of coastal Japan. In the waters off the Japanese coast, Pacific and Arctic Loons historically cooperated to herd Pacific sandlance into dense bait balls near the surface — a behaviour that Japanese fishermen learned to exploit. The practice, known as 'loon fishing' (uminari-ryō), allowed fishermen to follow the diving birds and net the concentrated fish beneath them. Accounts from the Meiji and Taisho periods describe fishermen earning an entire year's income in just two months — February and March — by working the loon-herded shoals. The birds were not merely tolerated but revered: in coastal fishing communities, loons were regarded as messengers from heaven, and harming one was considered deeply unlucky. The practice has since ceased, driven by loon population declines, the collapse of sea bream stocks, and the industrialisation of Japanese fisheries.

In Arctic Indigenous cultures across North America, loons hold broad spiritual significance. The haunting calls of loons — including the Pacific Loon — feature in the oral traditions of Inuit and Yupik peoples, where they are associated with transformation, the spirit world, and the arrival of summer. Loon imagery appears on traditional clothing, tools, and ceremonial objects across the circumpolar north. Pacific Loons and their eggs are still harvested in some communities as a traditional food source, a practice that predates written records and continues under subsistence rights in Alaska and Canada, though the population-level impact remains poorly quantified.