Marsh wrens commonly return to the same breeding territories year after year, making an orb-shaped nest with a side entrance. The male may construct 14 to 20 dummy nests when setting up a territory. Photo: J. Morton Galetto
One of the creatures I’ve enjoyed seeing on my paddles and meanderings around the bayshore is the marsh wren. The male’s continual calling, despite his often-elusive behavior among the reeds, is always intriguing. Finding his woven nest, with its side entrance hole, hanging in marsh grasses can be just as much a challenge as spying the bird itself.
In North America there are few nest weavers that build an enclosed nest that hangs. The male’s propensity to build more than one abode to mark out his territory and to attract mates increases the opportunity to find a nest. Thick reeds can make it a challenge, but since males often build “dummy nests”—and the female may also build a nest or complete one a male has started—that raises the likelihood of spotting one. In either event the female lines her choice with fine plant materials and feathers. While the male may build 14 to 20 nests marking his territory, only one to three nests are commonly used by his mates.
Often, wrens will use dummy nests in the nonbreeding season for shelter. These can also lure predators to a nonproductive nest versus an active one.
As their name indicates, these birds like marsh habitats that are characterized by vegetation such as bulrush, cattails, and cord grass. In our region, they prefer the shallow tidal and freshwater marshes on our coastal rivers.
Sometimes wrens are more easily spotted along the roads that go out to the New Jersey Delaware Bayshore if the vegetation is a thin strip of shrubs, as you find on Hansey Creek Road or Money Island Road.
When I’m motor-boating on the Manumuskin River I often turn off the engine to hear the calls of the male. Only males sing, while females give a click call. The males warble for extended periods of time, especially in the morning and often after dark as well. Hearing their song across a marsh in the middle of the night is a lovely experience. Their long calls are sometimes described as gurgles that are territorial declarations. During nest building they often give off a nasal buzz to attract mates.
They are so noted for their calls that a group of them is often referred to as a chime. I’ve seen them primarily as solitary or in pursuit of a mate; the only collection I have seen is a recently fledged family. But they are well known for their loud calls and chime surely seems a fitting designation. Other collective names are flight, flock, and herd of wrens.
Young fledgling already displays the wren’s iconic up-tilted tail. Photo: J. Morton Galetto
Marsh wrens are polygynous and try to attract more than one partner, which partly explains their building more than one nest. When the male has successfully connected with a female, his call may change to a melodious, rolling warble. Quite the Romeo!
There are a number of calls associated with the species, each with specific intent—pursuit, perceived intruders, mating, courtship, and such. Scientists that study sonograms of bird calls find that there are many more intricacies than first noted. The male’s song is often several chirps followed by a trill (a rapidly changing rolling call or flutter). Males also make a scolding buzz at intruders. Studies have shown that their communication is a learned attribute.
Most species of birds are monogamous, so some texts use the marsh wren as an example of polygyny in birds. Females have a greater investment in their embryos from both a size and numbers perspective. They have only a few eggs and they must invest great effort in incubation and feeding of their brood. So they must be careful in selecting a mate. The male, on the other hand, has microscopic sperm that are more abundant and thus he can fertilize more females’ eggs, improving his chance of selecting a suitable female.
The Birder’s Handbook offers this summation: “A male with a weak or otherwise unfit female loses a small part of his reproductive potential; a female making a similar mistake may sacrifice all or almost all of hers.”
Explanations of female mate selection delve into territory quality—especially as it relates to abundance of food resources. One study found that even if bachelor males are available in a marsh complex, females are attracted to territories that are the richest in insect populations, and they will choose to select an already coupled male who has staked out a territory with the greatest food resources.
Males are known to puncture the eggs of other species that intrude in their territory. Some nests commonly attacked are red-wing blackbirds and least bitterns. They have even been known to destroy the eggs of their own mate. Blackbirds, in turn, recognize marsh wrens as an enemy and will often destroy their eggs when found.
Cornell Lab of Ornithology found few studies of the predation they suffer from other species, although mice, rice rats, snakes, and weasels have been identified with nest failures.
Marsh wrens have four to six eggs in a clutch, which are incubated for 12 to 16 days. Only the female incubates the eggs although the male helps rear the chicks. The young birds fledge in about two weeks. They retain their parental dependence for about two weeks more until the female starts a second brood. The young learn to forage in vegetation close to water; they are insectivores feeding on the water’s surface and among marsh plants. Because they generally feed at the base of plants it can be difficult to spot them.
Marsh wren nests are often used in the off-season for shelter. Photo: J. Morton Galetto
The pugnacious marsh wrens are formidable foe and protect their territory with vigor. Photo: Steve Gifford
Scientists analyzing their stomach contents have found their diet to include bees, wasps, ants, aphids, moths, leafhoppers, beetles, dragonflies, and crickets. In freshwater aquatic habitats like those along our rivers, aquatic insects play an important role in their diet as well.
Herbert Kale of the University of South Florida studied the water sources of marsh wrens. He concluded that in freshwater they readily drink, but in salty areas they rely more on succulent food sources. He concluded that their small salt gland probably doesn’t play an important role in salt excretion. Further, he observed that morning dew on vegetation provides an additional freshwater resource.
The species is a year-round inhabitant of our area, although the resident winter birds are lower in numbers than the population following the arrival of mid-April migrants. These travelers come from states with warmer coastal climates south of New Jersey, but by late November we return to our winter resident levels. So right now is the time when you will see an increase in their presence in our local marshes. Happy birding!
Sources
Kale II, H. W. (1967b). Water sources of the Long-billed Marsh Wren in Georgia salt marshes. Auk 84:589-591.
iBird, Interactive Field Guide to Birds
The Birder’s Handbook: A Field Guide to the Natural History of North America Birds, by P. Ehrlich, D. Dobkin, D. Wheye, 1988
Cornell Lab Birds of the World, Marsh Wren, D. Kroodsma and J. Verner. birdsoftheworld.org
Photo: Steve Gifford
Marsh Wren Identification
Length: 4.5-5 inches (males slightly larger than females but similar plumage)
Only the male sings, and since he is vocal that is often distinguishing
Primary color: Brown
Size: 5-9 inches
Underparts: Buff – solid
Upperparts: Brown with black and white streaks
Eye color: brown
Head pattern: Dark cap, light eyebrow
Forehead: Dark brown
Nape color: Brown with black and white streaking
Throat: Pale grey
Flight pattern: Weak fluttering flight of short duration
Wingspan: 5.5 to 7 inches
Tail Shape: Fan-shaped
Tail pattern: barred
Upper and under tail: Red-brown and black barring.
Source: iBird, Interactive Field Guide to Birds. Phone application.
Highly recommended phone applications for bird identification – iBird, Sibley’s Guide, or Merlin.
