Hooded merganser, photo by Mick Thompson
We always enjoy seeing hooded mergansers, especially when the males have their crests — also known as their “hoods” — raised and are in courtship display. The scientific name for hooded mergansers is Lopodytes cucullatus that means “hooded diver.” The crests can be raised and lowered in both sexes, and are a helpful identification guide for these small fish ducks, who with their narrow serrated bills, catch fish.
Early naturalists in the 19th century listed hooded mergansers as “abundant” in Wisconsin and were found especially in forested areas near water. But Sam Robbins wrote in Wisconsin Birdlife in 1991 that hooded mergansers are uncommon summer residents in southeast Wisconsin. Columbia and adjacent counties were not not included in his breeding map for the species. Their numbers greatly declined due to loss of forested habitat that provided nest cavities and over harvesting by hunters. Sam wrote that “Theoretically, the bird’s summer range should blanket the state.”
According to the Cornell Lab of Ornithology “Hooded Mergansers are fairly common and their populations are stable and possibly increased between 1966 and 2015, according to the North American Breeding Bird Survey.”
Hooded merganser range map, provided by The Cornell Lab of Ornithology
We observed their numbers increase in Columbia County in the past four decades. In the 1980’s, we would see a few birds usually in spring migration. In the 1990’s, we began seeing a few nesting pairs. In the first Breeding Bird Atlas (1995-2000), hoodies were confirmed nesting in 12% of the statewide priority and 17% of the priority blocks in Columbia County. In the second Breeding Bird Atlas II (2015-2019), they were confirmed in 26% of the statewide priority blocks and 33% of the Columbia County priority blocks.
A freon nesting tube that was donated to us by the LaCrosse County Conservation Alliance. We replaced the freon tube with a cedar box. Photo by Richard Armstrong
Hooded Mergansers at Our Cabin Near Rio
We had two surprises on March 25th when we began our final check of our duck nest boxes at our cabin near Rio to make sure they were ready to go. The first surprise was finding two boxes that contained screech owl pellets. One of the boxes also contained a small uneaten bullhead. Usually one does not think of owls that go fishing.
The second surprise was finding two nest boxes with hooded merganser eggs. One box had four eggs and the other had two eggs. So far at the cabin we have three merganser nests with the first eggs laid on March 21, 23 and April 1st. An early ice out and above normal temperatures probably contributed to the early egg laying.
Lovely merganser eggs. Photo by Mark Martin
Our plan at the cabin is to check 20 accessible nest boxes weekly and stop checking individual boxes after finding woodie or hoodie eggs. We also have three nest boxes with wood duck eggs that were first laid on April 3, 4, and 5.
Nesting Hooded Mergansers at Goose Pond
Goose Pond contains an abundant population of fathead minnows, probably ideal prey for these small diving ducks. But in the past, the property lacked large trees with nesting cavities. That changed in 2015 when we erected two cavities as wood duck boxes. One box was placed at a wetland at Sue Ames Prairie and the other just west of the railroad tracks in the wetland south of the Kampen Road residence.
A hooded merganser nest was found on May 12 at Sue Ames Prairie. We checked the nest box on May 18th and the young were ready to jump out. Nine membranes from hatched eggs and one unhatched egg. This was the the first hooded merganser nesting at Goose Pond. Photo by Mark Martin
On May 12, 2016, Mark, Jim and Kathy Shurts, and grad student Heather Inzalaco conducted a big day count and Mark decided to check the nest box at Sue Ames Prairie. Mark slowly opened the side and could see an incubating female hoodie - what a surprise and a treat! Mark checked the box again on the 18th and nine young were getting ready for “jump day”. This was probably the first record for a hooded merganser nest at Goose Pond!
Hooded mergansers have used this box every year since 2016. Last year the box contained a large clutch of eggs that did not hatch. We speculated that the female abandoned the nest, was killed, or that this was a dump nest and not incubated.
However, one evening last July we looked out the large south window of the house on Kampen Road and saw a large brood of hooded mergansers! We were fortunate to watch them grow up. The brood started with 14 young and ended with twelve. The nest box near the brood was checked and many egg membranes and three unhatched eggs were found. Our guess is that both nest boxes were dump nests and only one was incubated. Late last month, Graham Steinhauer checked the box at Sue Ames and found a hoodie nest with the first egg laid on March 26th.
Hooded merganser cuties, photo by Mick Thompson
When we put up our “wood duck” boxes, our goal was to attract wood ducks, and did we not expect to have nesting hooded mergansers. As of 2020 we still do not have any records of nesting wood ducks, but the hooded mergansers are sure making themselves at home!
A question that some visitors ask is, “Why aren't male hooded mergansers present in Columbia County after mid-April?” It is often mentioned when looking up information on hooded mergansers that after the hen begins incubating the male takes off. Most waterfowl biologists believe they head to wooded river systems and may travel long distances.
Special thanks to Mark and Jenny McGinley who have been erecting, repairing, cleaning out and monitoring 41 wood duck boxes for the past 11 years that at the Anderson Waterfowl Production Area (WPA), Jackson WPA, Otsego Marsh and Schoeneberg Marsh WPA/Erstad Prairie. All areas have high numbers of nesting woodies and hoodies.
Jenny McGinley checks on of their many wood duck boxes, this one at Otsego Marsh. Photo by Mark McGinley
In the past eight years, Mark and Jenny found 193 successful nests including 123 (64%) nests that were only wood ducks, 31 (16%) that were only hooded mergansers, and 39 (20%) that contained eggs of both species (dump nests). Both species can also lay eggs in the nest of their species. Mark and Jenny have found dump nests with up to 33 eggs! Large clutches usually do not hatch since a female would have a hard time incubating large numbers of eggs.
Hoodie females begin nesting at age two, usually lay a clutch of 10 eggs and incubate the eggs for 32 days while woodie females begin nesting their first year, usually lay a clutch of 12 eggs, and incubate for 30 days. It is easy to look at eggs and identify the species since hooded merganser eggs are large, white, thick-shelled and spherical contrasting to smaller, brown, thinner-shelled, oblong eggs of the wood duck. It is assumed that since wood ducks have a shorter incubation period that more wood duck eggs might hatch in dump nests that also contain hooded merganser eggs. We assume that if a female wood duck is checking out nesting cavities and finds a defensive hooded merganser already nesting that she would look for another cavity.
A wood duck box should have a solid predator guard to protect the eggs from hungry raccoons and other critters. Photo by Mark Martin
Consider putting up a nest box to attract a breeding pair. Attach a predator guard to keep predators from raiding eggs and young.” Note that “wood duck box” blueprints work well for attracting hooded mergansers. Here are some instructions published by National Audubon on how to build a duck box. Some people use pine, but we recommend cedar for its excellent rot resistance. Be sure to add a predator guard as raccoons and other critters love to eat duck eggs.
If you would like to see a brood of hoodies visit Schoenberg Marsh Waterfowl Production Area adjacent to Madison Audubon’s Erstad Prairie, or MAS’s Otsego Marsh property south of Rio. The young are fun to watch diving, feeding and interacting.
Written by Mark Martin and Sue Foote-Martin, Goose Pond Sanctuary resident managers
