A common eider drake. (ISTOCK PHOTO)

During the winter months, our local population of oceangoing ducks soars as migrants arrive from hundreds or thousands of miles to the north. Buffleheads, surf scoters, longtails and others find shelter and food in Harpswell waters. One of my favorites is the largest sea duck, the common eider. You can identify these striking birds at a distance by their wedge-shaped heads, and the drakes are cloaked in jet black and brilliant white feathers.

Common eiders are fascinating birds, capable of flying 40 miles per hour just above the water despite weighing up to 7 pounds. While they have been observed eating fish, algae and seeds, the primary foods for eiders are shellfish and crustaceans. Watch eiders foraging along a rocky shore, diving to 30 feet or more, and observe them swallowing intact mussels or sea urchins.

The birds have long been a source of meat and eggs, and prized for the breast feathers known as eiderdown. As often happens when we target wild creatures for commercial purposes, eiders suffered drastic declines from over-harvesting, pollution, gill netting near the shore, and lower availability of their preferred foods. They were nearly extirpated by the early 1900s, but gained some protection under the Migratory Bird Act. In “Birds of Maine,” Peter Vickery reports that as recently as 2007, there was just one breeding pair of common eiders in Maine. Fortunately, the population has rebounded to 20,000 pairs.

But eiders have recently been struck by bird flu, specifically highly pathogenic avian influenza, or HPAI. We’ve heard about HPAI since 2009, when the virus emerged among domestic ducks and geese in China. The virus still circulates among wild birds that encountered domestic flocks. As with COVID-19, the HPAI virus has mutated and can affect new species. Unlike the COVID-19 virus, HPAI rarely spreads to humans, but the original virus in Asia caused mortality to reach 50%. To date there are no human cases of HPAI from the current strain of the virus, H5N8.

We are fortunate to see eiders in local waters around the calendar, but we are near the southern limits of their breeding range. Common eiders, and the closely related king eider and Steller’s eider, may be found in northern waters globally, where they favor subarctic and marine habitats for breeding. Some birds we see locally migrate as far south as Maryland in search of ice-free water and abundant food sources. Eiders may gather in flocks of 1,000 or more birds, which puts them at risk of contracting diseases like HPAI.

The Maine Department of Inland Fisheries and Wildlife recently issued an advisory to alert the public about the risks of HPAI when handling common eiders. During the 2022 breeding season in the St. Lawrence Seaway, there was an outbreak of HPAI that caused the death of as many as 15% of nesting female eiders. While HPAI has been detected among wild and domestic birds in several Maine counties, some birds are more resistant to the disease than others. Surviving birds may carry the virus to new locations during migration. The upshot is that many of the St. Lawrence birds migrate to Maine, where they are a preferred target of waterfowl hunters.

The Department of Inland Fisheries and Wildlife noted that consumption of eiders and other waterfowl continues to be safe when the meat is properly cooked. There is a two-fold risk when handling harvested birds — either that a hunter could encounter the virus, or that careless disposal of carcasses may allow the virus to spread to other birds. This is a particular concern for people keeping domestic waterfowl, since the discovery of HPAI in such flocks typically results in extermination of all birds. In addition, the Department of Inland Fisheries and Wildlife is asking hunters to voluntarily observe a moratorium on harvesting female and juvenile eiders to avoid further stressing the population.

Hunters should exercise caution in processing harvested birds, using masks, gloves and other protective clothing, and carefully disinfecting any equipment or surfaces that come into contact with birds. Boots that may be carrying bird droppings should be cleaned using a mix of water and bleach.

The global population of common eiders has been estimated at more than 3 million, but the bird is considered “near-threatened” in view of a long-term decline in numbers. Let us hope that the impact of HPAI soon moderates so that we can enjoy these beautiful birds along our shores for the long haul.

Ed Robinson’s latest book, “Nature Notes from Maine Vol. II: Puffins, Black Bears, Raccoons & More,” is available from the Harpswell Heritage Land Trust. All profits support HHLT’s conservation and education efforts.