Marsh Wren, Jackson Bottom Wetlands, Hillsboro, Oregon on 5 April 2009 by Greg Gillson.The tiny Marsh Wren creeps mouse-like through the reed canary grass (as above) at your local wetlands. They favor cattail marshes and emergent vegetation, but they don't require much territory--a small cattail puddle along a country road ditch may do. Where the habitat is extensive, their population can be fairly high.
Shy and secretive, they would be very difficult to detect in their soggy habitat if not for their loud spring and summer songs and harsh call notes. The male may crawl up to an exposed tip of grass or wild rose bush to sing their rattling reedy trill.
They also pugnaciously defend their territories from other Marsh Wrens and larger birds, including Red-winged Blackbirds and Yellow-headed Blackbirds--even destroying the eggs of the blackbirds nesting within the wren's territory.
The males may build several to more than a dozen oval "dummy" nests among the marsh vegetation. A single male may also have more than one mate at a time, each female having her own nest. The females guard their own nest against other females, while the males guard their territory (which may include one or more nests) from other males.
The population movements of this species across North America are complex. The same is true in the Pacific Northwest. West of the Cascade and Sierra Nevada mountains, where extended days of sub-zero winter maximum temperatures are rare, these wrens seem to be residents. However, in many areas winter numbers are significantly less than breeding numbers. Coastal marshes tend to have more wintering birds than breeders. East of the Cascades, birds arrive on territory in April and birds remain into September, gradually dropping in numbers. They may winter at favored sites with open water.
So, the next time you are out at your local pond with weedy grasses and cattails poking up above the water, look for this interesting little bird.