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July 2009
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Merganser Moms

I’m going to be afield for most of the upcoming week with limited internet time, so I thought I’d get one more short post up before I leave.  First, I want to thank Jeff Gordon for his flattering introduction of me over on his blog.  Thanks too, to the folks at Nature Blog Network, as well as many individual bloggers and blog readers who have taken the time to check out my site!

As I mentioned a few posts back, I recently spent a week in the Catskills enjoying a wonderful river valley.  I’ll be sharing photos and nature tidbits from that trip in a series of posts.

The first really fun observation I would like to share is the experience of watching female Common Mergansers shepherding their large broods of chicks while the youngsters learned to fish.  During our stay, the several local merganser broods would travel up or down the river, passing in front of our cabin only when we were inside, or around the back not paying attention!  One female had a group of 14 chicks, while another nearby female herded only 6 or 7.  (The largest known clutch is 19).

This quiet stretch of river was a favored spot for Common Merganser fishing lessons.  The cabin is visible on the far side of the river among the trees.  Photo (c) 2009 Matthew Sarver

This quiet stretch of river was a favored spot for Common Merganser fishing lessons. The cabin is visible on the far side of the river among the trees. The rock in the foreground is now called Eagle Rock, since a Bald Eagle used it as a staging area for its bath on our list visit. Photo (c) 2009 Matthew Sarver

At first, I was disappointed that I did not have the opportunity to photograph the merganser broods (a task that surely would have required me to build a blind by the river’s edge).  Later, though, I discovered that George Miksch Sutton had written this wonderful description of his encounters with merg broods on his trip down the Abitibi River with W.E. Clyde Todd in 1923:

The Abitibi was far more than a series of rapids, cataracts, and portage trails.  There were beautiful quiet stretches down which, aided by the strong current, we must have made up to five knots or more.  A notable feature of the birdlife were broods of half-grown common mergansers, each brood with its mother, all of them, mother and young alike, flightless, she in her late summer molt, they with their first major wing feathers only partly developed.  The close-knit companies dived when they saw the distant canoe approaching; when hard-pressed, however, they did not dive but rushed off half-standing, churning the water furiously, bodies weaving from side to side, wings not flailing the air but folded in tightly, thus protecting the stubby blood quills.  The noise of their sudden departure was startling, for it contrasted so sharply with the silence of the sequestered spots the birds so obviously enjoyed.  One fact about this truly common species, which the guides called the sawbill, impressed me greatly: not a single adult drake did we see during our descent of that mighty wild river!

-G.M. Sutton 1980. Bird Student: an Autobiography (p 125)

The Abitibi River at Iroquois Falls in northeastern Ontario. Photo by P199 on Wikimedia Commons. Used under a Creative Commons License (Attribution Share-Alike 3.0 Unported).

The Abitibi River at Iroquois Falls in northeastern Ontario. Photo by P199 on Wikimedia Commons. Used under a Creative Commons License (Attribution Share-Alike 3.0 Unported).

Common Mergansers nest in tree cavities, often using old Pileated Woodpecker excavations, and also sometimes in crevices among rocks.  The chicks leave the nest and follow their mother to the water.  Since young chicks can’t fly until they are more than 2 months old, it’s a long summer for merganser moms.

Females frequently brood parasitize other females of the same species by laying their eggs into the nest of the other female.  Another common, but poorly-studied phenomenon is the joining of several partly-grown broods under the care of a single female, knows as brood amalgamation.  While this happens frequently, it is unknown whether more aggressive females tend to “take over” other broods, or if the adoption of these chicks is simply the result of confusion on the part of the youngsters.

Because of these complications, it is impossible to know exactly how many chicks are actually the offspring of their apparent mother.  None of this is the male’s problem, however, since as Sutton observed, they are nowhere to be seen during this period.  The pair bond apparently ends at incubation, but where do the males spend their time during mid-summer?  Do they hang out in trees, enjoying the cool mountain shade?

According to A.C. Bent’s Life Histories:

The drakes desert the ducks and usually disappear from the breeding grounds entirely as soon as the eggs are laid, leaving the females to perform the duties of incubation and care for the young alone. In Newfoundland we saw only females on the lakes, where they were busy with family cares, but we saw plenty of males on the swift water rivers, playing in the rapids and fishing in the pools. Several observers in Maine have said that the males are not seen during the summer, but this may be due to the fact that the males are in eclipse plumage at this time and are very shy and retiring.

Can anyone out there shed some more light on the mystery of the missing merg males?


4 comments to Merganser Moms

  • Doug Harbaugh

    A black snake in our backyard met an untimely end when it got caught in the netting used to protect a Japanese Maple tree from hungry herbivores. Entanggled in the net and unable to escape it became easy prey for we suspect a hawk. The unknown preditor left behind enough of the snake that we guess its length to be 36 – 40 inches. We will miss that snake, he kept other pests in check for us.

  • Lynn

    I live on Lake Simcoe in Canada, the province of Ontario. I have been reading through all the web sites describing Common Merganzer behaviour. Specifically I am interested in their brood amalgamation as you have refered to it. Routinely I have seen every large broods. This summer I counted 72 chicks and only one poor MOM. Your is the first site I was able to get some information on this behaviour. I have been referring to it as birdie daycare. I was very intested in the selection of the mother that got let with the job. Thanks for shedding some light.

    • Hi Lynn – Thank you so much for reading and I’m glad you found the post helpful. 72 chicks is amazing! I’ve never heard of a count that high. That must have been one STRESSED OUT mom!!

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