Shallows

Year-Round Bay Birds

Common mergansers are year-round residents of Kwilákm, and a common sight along any Bowen shore, and top predators in the aquatic food chain. When you look over the ducks in the Bay or the Lagoon, common mergansers are handsome birds. Distinguishing the drake (male) from the hen (female) is easy when the birds are in breeding plumage from roughly October to June. He has a bright red bill and metallic green head, while the hen sports a copper-coloured crest. Between late summer and mid-autumn, however, things become a bit confusing as males nonbreeding plumage looks very similar to female plumage. Come springtime, the females appear to vastly outnumber the males because many first-year male mergansers have not grown into adult plumage and still look mostly like females. But just because a merganser looks like a female, does not necessarily mean it is a female.

Common mergansers’ main food is medium-sized (5 to 30 cm) fish such as herring, anchovy, young salmon, shiner perch, sculpins, stickleback, and flatfish.

Their narrow, unducklike bill has evolved to help in the capture and handling of fish. Toothy serrations along the edge grip struggling fish. The prey is seized and forced head-first down the expandable gullet. When schools of fish are available, mergansers can fish in packs, rushing upon their prey in line, darting and seizing.

Researchers have determined the average daily consumption of fresh fish by an adult common merganser is about 450 grams.

Gulls often follow mergansers as they forage, waiting for the ducks to come to the surface with a fish, and then try to steal their prey. This practice is called kleptoparasatism.

Common mergansers are cavity nesters. The hen searches for a large, old or decaying tree or snag. They prefer a site near water and 3 to 8 metres up a tree. Mergansers cannot chisel their own cavity, so they take advantage of excavations left by pileated woodpeckers.

Landowners near Kwilákm are encouraged to preserve large snags on their land as important nesting habitat for woodpeckers and the merganser families that will inherit those nest sites when the pileated woodpeckers are through with them.

Bowen’s citizen scientists have observed mergansers nesting in tree cavities along Terminal Creek by the Meadows. Bowen has many suitable snags with woodpecker holes for nesting. The large population of common mergansers living on Bowen attest to this. When such holes are not available, mergansers may nest on the ground or use nesting boxes such as those erected by the ramp at the Union Steamship Company (USSC) Marina.

Nest boxes can take the place of woodpecker nest holes if your property is small and/or all larger trees have been removed from your lot. Cornell University’s Ornithology Lab offers common merganser nest box information and free building plans: nestwatch.org/learn/all-about-birdhouses/birds/common-merganser.

Young mergansers can swim and feed easily as soon as they leave the nest, although for the first few days, most of the food is obtained on the surface. Fledglings at first feed mainly on aquatic insects. They become skilled divers within eight days of leaving the nest and by about 12 days can catch fish. The brood responds quickly to female alarm calls and runs in unison across the water when fleeing from a perceived threat. Young common mergansers become independent in five weeks; are able to fly when about 65 days old; become reproductively mature by their second summer; and can live for a dozen years.

Because of mergansers’ fish diet, putting them at the top of the food chain, common merganser are important indicators of the overall health of aquatic ecosystems. Common mergansers seem to be doing well in our waters. Twenty years of citizen science data, collected by the British Columbia Coastal Waterbird Survey (BCCWS), has examined trends in abundance of 50 species in the Salish Sea. The BCCWS data shows a steady increase in Salish Sea common mergansers of almost 3%/year between 1999 and 2019.

A Merganser Nest Box in Snug Cove

Bowen photographer Mary Le Patourel caught this picture of mother merganser taking a break from sitting her clutch of 9 to 12 eggs in this box at the Union Steamship Marina in Snug Cove. The hen incubates continuously through the night for about 30 days. She takes several recesses during the day, such as seen here. Once hatched, the young remain in the nest for a day or two before tumbling from the nest cavity to follow the female to nearby water.

Mary tells of the events leading to her photo of mother common merganser with her ducklings in the Lagoon.

These young mergansers fledged from the merganser boxes at the USSC Marine. There are two boxes and each year two broods emerge about the same time as the Round Bowen Island Sailboat Race in early June. This year, this brood hatched the same day as the Race and as the sailors were heading up the ramp to the beer garden, mother duck was below, urging her chicks out of the bird box at one-day-old. Mother quickly assembled her youngsters on her back, and she swam under darkness to Kwilákm. There were more than 10 chicks to start with and the last time I saw them, there were four left. That’s pretty good considering the eagles and crows have to feed their young at the same time of year.

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