Birder’s Notebook: Yellow-billed Loon––King of the loons

On a recent drive along the coast east of Cape Nome, the majestic silhouettes of two young yellow-billed loons caught my eye and stirred excitement. It is not a bird I see often. The loons’ exceptional size and the distinctive upturn of their ivory-colored bills gave them away amidst a raft of gulls and black scoters.

The Bering Strait region is a breeding ground for all five of the world’s loon species. The magnificent yellow-billed loon, which nests in northern tundra regions across Alaska, Canada, and Russia, is the largest and rarest of them all.

Yellow-billed loons nest along the shores of large, deep, clear, tundra lakes that support an abundance of small fish. Such lakes are especially prevalent in the lowland and upland tundra regions of the northwestern Seward Peninsula in the Bering Land Bridge National Preserve. There, yellow-billed loons are fairly common, regular breeders. National Park Service biologists monitor that breeding population and estimated 250 breeding pairs as of 2021.

Additionally, throughout the summer nonbreeders appear infrequently along coastal shores from Safety Sound to Cape Espenberg. Yellow-billed loons are also seen at St. Lawrence Island, where a few breed, and others pass by during spring and especially fall migration.

Yellow-billed loons form monogamous pair bonds and return faithfully to the same nesting lakes year after year for the lifetime of the pair. If one of the pair fails to return, the surviving mate likely takes a new mate.

Pairs typically arrive in the region toward the end of May. They occupy their traditional lakes soon after arrival or as soon as there is some open water, fishing under the ice if the lake is not completely thawed. Birds that arrive early in the season have a greater chance of keeping their territories.

There is intense competition for limited, suitable nesting lakes. Pairs use vocalizations, displays and outright attacks to defend their lake against other loons of all species and even diving ducks. Encounters are frequent and sometimes lethal to one of the combatants, especially if the loon dives and impales an intruder from below with its large, daggerlike, ivory-colored bill.

Nests are placed on lakeshores or islets. The pair constructs their nest together using vegetation and mud from the immediate vicinity, often refurbishing a previous nest bowl. They add additional material during incubation.

Egg laying occurs in June and incubation begins when the first of two eggs is laid. The parents share incubation and chick-rearing duties.

The chicks hatch in about 28 days, covered in down. They are able to leave the nest and swim briefly with a parent within a day, returning to the nest if the second egg is still being incubated. The nest is abandoned a day after the second chick hatches.

The chicks are brooded periodically on shore until they can regulate their own body temperature, in eight to nine days. Occasionally chicks may ride on a parent’s back, but that is rare. The presence of predatory pike in the lake or a high risk of predation on shore may result in this behavior.

Usually only one yellow-billed loon chick survives. Mortality rates for the younger chick are high. Sibling rivalry and mortality are greatest during the first three days after hatch.

It takes about three months for chicks to develop sufficiently to fly. Fledging occurs between mid-September and early October. The large, deep lakes used by yellow-billed loons freeze later than smaller ones, giving the young loons more time to develop.

Yellow-billed loons are almost exclusively fish eaters, but small amounts of invertebrates and plant materials are also eaten.

Loons are visual hunters, often peering underwater to locate prey before diving. They swim powerfully in pursuit of prey, propelling themselves with their large, web-toed feet.

In the Bering Sea region, least cisco and ninespine sticklebacks are two of the most abundant and energy-rich freshwater fish species and are probably particularly important foods during nesting and brood rearing.

Yellow-billed loons are twice the size of Pacific loons and their large body size has a cost––it takes a lot of energy to fly. Therefore, usually the species selects very large breeding lakes with abundant fish to minimize the need to fly to other lakes or marine waters for food. However, telemetry studies on the Seward Peninsula show that parents make daily trips to feed in marine waters. This is perhaps explained by the use of smaller lakes here than are typically used in Arctic regions.

Young begin fledging in mid-September, and families leave their nesting ponds for marine waters almost as soon as the young can fly. The adults’ pair bond ends for the season when they leave their nesting lake. Some young remain in coastal waters through October.

Satellite telemetry studies of yellow-billed loons nesting on the Seward Peninsula found that 56 percent of the tagged loons migrated across the Bering Strait to winter off the coast of Japan, and 44 percent migrated along the west coast of Alaska to wintering areas in the Aleutian Islands.

Immature birds remain on their winter range until they mature at age three. Suitable breeding territories are limited and often occupied. It may take several years for returning youngsters to secure a nesting lake when they find either a vacant lake or out-compete an occupant. Until then they stay mostly on marine waters and fly inland to prospect for an available territory.

Research in the Bering Land Bridge Preserve indicates that all suitable lakes there are regularly occupied, which implies that the breeding habitat is saturated and cannot support more yellow-billed loons.

Yellow-billed loons are listed as near threatened and are an international species of concern. Factors that raise concern include the species’ small global population size, their low reproductive rate, breeding opportunities limited by their specialized nesting habitat requirements, and low genetic diversity in the population, which makes a species less adaptable to change.

Yellow-billed loons are considered the loon most vulnerable to climate change, which is already impacting both their freshwater and marine habitats. Permafrost melt is causing lake drainage both in the preserve and on the North Slope, reducing the availability of their limited breeding habitat. In addition, warming waters are altering the distribution of marine fish, which is adversely impacting many seabirds.

You too might get lucky and see one of these regal young loons if you scan coastal waters this fall.

* Photo by Kate Persons COMMON LOON – Note the black bill on this common loon in breeding plumage, which quickly distinguishes it from the yellow-billed loon, even at a distance. The common loon breeds in large lakes in boreal forests; it’s close relative, the yellow-billed loon, nests in tundra lakes. Once considered quite rare on the Seward Peninsula, common loons are being seen more frequently in recent years. These common loons were fishing in Safety Sound, which is a good place to look for them in summer and early fall.

Photo by Rodney Ungwiluk Jr. BREEDING PLUMAGE – Rodney Ungwiluk Jr. got an unusually close look at this yellow-billed loon in breeding plumage while boating near Gambell. The ivory-colored bill and larger white spots on the back distinguish it from its slightly smaller relative, the common loon.

Photo by Kate Persons JUVENILE – Juvenile yellow-billed loons such as this one show up in fall along southern Norton Sound to fish in coastal waters before migration. Even without the striking plumage of breeding adults, these large loons have a commanding presence. Keep an eye out for them through October.