The Common Merganser

April 15th, 2024

The spring weather was perfect for being out and observing this week. The water in Willits Valley is drying up in the grasslands and flowing nicely through the creek beds. There is still some inundation left on the north end of the Mitigation Lands. I must use knee-high rubber boots to walk through them. Walking along Outlet Creek, I disturb some Mallards and Wood Ducks who take off, calling loudly as they disappear downstream. Then I notice that there is a pair of ducks that are quietly swimming past with bright red hooked bills. These are a pair of Common Mergansers (Mergus merganser). This duck predates on fish and has a large body and a long, straight beak with a small hook at the end. The males and females do not look alike. The male is overall white-bodied with a dark green head. Their beak is a reddish-orange color contrasting with their green head, making them look exotic.

The female has a less colorful beak, more brown-orange, and is primarily gray with a rusty brown head and white chin patch. She can make her feathers stand up on her head like a crest. There is a clear distinction between her head color and her body color. Two other species of mergansers are found in Mendocino County, though one is rarely found inland. The Red-breasted Merganser is found primarily in coastal waters or bays and estuaries.

The third type of merganser, a Hooded Merganser, is sometimes found right next to the Common Merganser in our rivers and inland marshes.

One of the very interesting facts about Common Mergansers is that they can be cavity nesters. They nest less frequently in rock crevices, old sheds, chimneys, lighthouses, holes in banks, holes in the ground, hollow logs, and burrows. They readily nest in boxes, including those designed for the much smaller Common Goldeneye. Sometimes, they nest on the ground.

Common Mergansers mainly eat fish but will also prey on aquatic invertebrates including insects, mollusks, crustaceans, and worms. Frogs, small mammals, birds, and plants can also be consumed by mergansers. They find their prey by sight, often probing the sediments and underwater stones with their slender bills, which have sharp serrations for grasping slippery prey. I did not know they also ate birds and small mammals until reading about this on the Cornell All About Birds website. Looking at their long, hooked bills, it makes sense they might be predatory on other things besides fish. Outlet Creek does not have lots of fish in it, which means it is a good survival skill for these ducks to hunt and eat a variety of food.

As long as our creeks have water in them through the summer, Common Mergansers are found year-round. When we have dry years, and the creeks dry up, they move further downstream into the main Eel River system.