Nesting Marsh Wrens

Springtime wetlands in California's Great Central Valley resound with birdsong, a cacophony of beautiful and often strange sounds that can only be attributed to the wide diversity of avian life found here.  Take for example the maniacal laughter of the Pied-billed Grebe, the liquid "plumping" call of the American Bittern, the descending whinny of the secretive Sora, and the abrasive metallic screech of the Yellow-headed Blackbird.  Underpinning all of these weird wetlands sounds, you are also likely to hear another: the incessant, insect-like chatter of the Marsh Wren (Cistothorus palustris).

If you're new to birding, or maybe new to exploring our beautiful wetlands at all, the tiny Marsh Wren is a bird you might not be familiar with.  They are small, quick, almost constantly in motion, and tend to keep to the shelter of reeds.  In short, they are more often heard than seen and many visitors to wetland areas never know they exist.

But exist they do!  During the spring, it seems that every patch of tules across the Great Central Valley is home to a family of Marsh Wrens, though oftentimes the only clue to their presence is their chattering call.  I love hearing Marsh Wrens calling and scolding and chattering away, vehemently defending their territory.  To me, it is the sound of the very soul of our wetlands. 

Spend some time with a naturalist, and you will soon learn to pause when you hear that familiar chatter and wait quietly, peering deep into the reeds as you watch for the tell-tale quick flicker of movement that is a Marsh Wren darting between the tules.  Some days, that flash of brown might be all you are allowed to see; other days, your patience will be rewarded!  Your chances of getting a good, long look at a Marsh Wren are greatest during the spring nesting season, when males are more likely to perch in the open to sing in defense of their territory. 

Once you have spotted your first Marsh Wren, you will learn to recognize this little brown gnome of the wetlands by its white eyebrow and short tail that often sticks up into the air.  They are similar in appearance to House Wrens and Bewick's Wrens, but are nearly always confined to their beloved wetlands and reeds.  House Wrens are more widely spread, nesting in cavities in overgrown areas from forests to backyards, while Bewick's Wrens tend to favor areas of chaparral, scrubland and open woodland.

If you're lucky, you might even spot and learn to recognize the Marsh Wren's intricately woven oblong nest, suspended a few feet above the water in a protective clump of vegetation.

Male Marsh Wrens are the designers and builders of these woven homes, and each hopeful male builds several nests within his territory by weaving together strips of grasses, sedges and cattails.  Nests measure approximately seven inches high and five inches wide and include an access hole near the top.  Once construction is compete, the proud male shows his mate around each nest, letting her choose which she will line with cattail fluff, feathers, and bits of vegetation and subsequently lay her clutch of three to six eggs.  (Up to ten eggs have been recorded.)  One male may mate with multiple females, and while females incubate the eggs on their own, both parents feed the young.  As one male may have a few families of five or more young at one time, and females are capable of raising two broods each year, it's no wonder Marsh Wrens are hardly ever still!

According to Kaufman's Lives of North American Birds, one male may build up to twenty nests, most of which are never used for raising young.  They may be used for sleeping in by adult Marsh Wrens during other seasons, and I imagine that having so many "dummy nests" hanging around the wetland would be a good deterrent for would-be predators. 

While they are small, Marsh Wrens are feisty, and both parents actively and aggressively defend their nest.  I hate to say it, but Marsh Wrens commonly destroy the eggs and even young nestlings of other birds, including those of other Marsh Wrens as well as of larger marsh-dwelling species like Yellow-headed Blackbirds.  It can only be assumed that while they are naturally fierce competitors, Marsh Wrens are driven to more and more drastic measures as their niche habitat shrinks and resources become increasingly scarce.

But despite the loss of vast wetlands across North America, Marsh Wren populations remain stable and their incessant chatter remains a hallmark of our beloved freshwater marshes.