Moon snails' mysterious egg cases

Marsh wrens hide well, easy to overlook

Posted May 29, 2018 at 2:28 PM

Marsh wren hiding in cattails

Updated May 29, 2018 at 2:28 PM

Marsh wrens are fantastic little birds. If you have ever been in or near a freshwater marsh you have probably heard them chattering away from deep in the marsh. Sibley’s Guide to Birds describes their call as a musical rattling trill. I always hear them but never see them - they are secretive and difficult to see. This is certainly true. While out helping with our neighborhood marsh clean-up a few weeks ago, I finally saw one - it would pop up above the cattails, flying up with rapid, stiff wingbeats and then plunge back down into the cattails and disappear. I decided to go back with a camera and see what I could capture on film.

While difficult to see, marsh wrens are even harder to take a picture of -- they move so fast and generally stay hidden down in the grasses. I didn’t have a lot of success, just an eye or a tail, the rest obscured by the cattails. I did, however, learn a lot about their behavior. While out in a small section of marsh I found 3 different marsh wren nests and was able to observe mating/territorial displays and nest-building activity.

Marsh wrens (Cistothorus palustris) are tiny - similar in size to the common house wren that might live in a wren house in your backyard. Unlike house wrens (which are cavity nesters) marsh wrens build their nests out of cattails, grasses and reeds deep in a marsh.

Males arrive at the breeding grounds before the females and weave nests out of strips of cattails and other marsh grasses that are attached to cattails, 2 to 5 feet above the water. The nests are dome-shaped (I think of them as football-shaped) with a hole at the top and nest cup at the bottom (Cornell Lab of Ornithology). Males make just the shells of these nests, they don’t line them (that’s the females’ job). Males weave multiple nests (I’ve read that they’ll build between 6 and 22 nests) and use these nests to woo the females. There is also some evidence that these “dummy nests” might be used to fool predators. The extra nests also serve as winter roosts for non-migratory marsh wrens.

When the females arrive in the spring (marsh wrens that live in the north are migratory, southern marsh wrens are year-round residents), the males begin their courtship - this involves the male flying up and fluttering down, cocking his tail, singing and showing the female his different nests. He is successful when the female chooses a nest (sometimes she doesn’t, and he has to build more). Once the nest is selected, the female lines the nest with grasses, cattail down, feathers and rootlets (Cornell Lab of Ornithology). The wrens I was watching were doing just that, plucking cattail fluff and carrying it back to their nests.

Marsh wrens are polygynous - the males mate with more than one female. Oftentimes females will choose an already-mated male over a “bachelor” male, presumably because these males have the best territory, or the most nests, or exhibit some other evidence of their reproductive fitness.

Marsh wrens may be small but they are also ferocious competitors for resources in the marsh. They will destroy the nests and kill the young of other marsh wrens and blackbirds.

Marsh wrens are one of those birds that are easy to overlook unless you know they are there. I highly recommend going out to a marsh and listening for them. They are fairly noisy right now since it is the start of the breeding season and males are busy attracting females. Look carefully and you might see a ball of woven grasses suspended in the middle of some cattails - dummy nest or the real deal?