Many visitors to Goose Pond this spring and summer were rewarded by hearing the rich harsh staccato with few pure musical notes of the marsh wrens around the edges of the pond.
Sam Robbins wrote “In summer this is a “fun bird” to see and hear. You can stand near a cattail marsh before dawn, after dusk, or even in the middle of the night, and hear the delightful rattle of the “long-bill”. Once it is light, you can see considerable activity as the nervous birds move around.”
Marsh wrens, formerly called long-billed marsh wrens, can be confused with sedge wrens. The easiest way to separate the two is by knowing their preferred habitat. Marsh wrens live in deep or shallow cattail or river bulrush marshes while sedge wren nest in sedge meadows and wet to mesic prairies.
Most marsh wren nests are 2–5 feet above the ground and are dome-shaped, with strips of cattail, sedges (bulrush), and grasses woven together. The nest is oblong with a small hole at the top and an enclosed cup at the bottom. The nest is about 7 inches tall and 5 inches wide. Females line the active nests with strips of grass, sedge, cattail down, feathers, and rootlets. Clutches can range between 3-10 brown spotted eggs and the incubation/nesting period is 25 to 31 days long.
Males migrate north before females and build a number of nests in preparation for their arrival. Once the females arrive, the male escorts the lady he is courting to his various nests, putting on quite a display of bowing, bobbing, and showing off his tail and his handiwork. The female selects a mate and she may build her own nest if his nests do not suit her. Together, they defend their nesting territory, and even destroy the eggs and nestlings of other marsh wrens and nesting birds. Males often mate with multiple females in the area (does he take these ladies on the same tour of his collection of nests that the previous female dismissed as inadequate?).
Our goal this year was to confirm marsh wrens nesting at Goose Pond. Wisconsin Department of Natural Resources staff Daryl Christensen and Sumner Matteson found 10 males calling in mid-June while surveying for eared grebes, but unlike some other bird species (like eared grebes), marsh wrens cannot be confirmed by seeing the birds carry nesting material. A pair can build a number of “dummy” nests, and in fact, researchers have found that male marsh wrens may build up to 22 nests!
The first week in July, Goose Pond manager Mark Martin, land steward Graham Steinhauer, and interns Siena Muehlfeld, Tanner Pettit, and Henry Weidmeyer searched for marsh wrens on the north side of the pond. This was a new experience for the interns and they thought it would be easy to confirm nesting for the Breeding Bird Atlas project. It started out strong: six males were found calling in a two-acre area.
When the first of 12 nests was found the interns thought that the species was confirmed. Mark mentioned that marsh wrens build many nests, so a confirmed nest has to contain eggs or young. Since one cannot see into the nests, and Mark recommended they gently poke a finger through the entrance hole and see if eggs or young could be felt. At nest #10, Tanner found a nest with 3 eggs – a new confirmed species at Goose Pond! And those six singing marsh wrens? Tanner noted that “nests were always found near singing males.”
The federal breeding bird surveys conducted in the United States from 1966 to 2015 found an increase in marsh wren numbers by 130% and researcher estimated their population at 9.7 million, putting them in to the category of "low conservation concern." However, draining and filling wetlands and marshes could create problems for this species. Conservation Biologist Randy Hoffman said that the largest numbers of marsh wrens in North America is found at Horicon Marsh, which is also the largest cattail marsh in North America.
We are still on the look-out for marsh wren nests, as there's still time for nestlings to grow big and strong enough to make the fall migration to Florida, Texas, New Mexico, Arizona, and Mexico. On July 24, Daryl and Sumner checked on our wetland birds and found six males still calling and observed males carrying bulrush leaves to the arrowhead for constructing nests. Will we have another chance to gently poke our fingers into nests and find more eggs? Stay tuned to find out!
Written by Mark Martin and Susan Foote-Martin, Goose Pond Sanctuary resident managers, and Brenna Marsicek, director of communications
Cover photo by Arlene Koziol