An active species, the marsh wren gets its scientific name from two Greek words, cistos and thouros, meaning ‘shrub’ and ‘leaping’, respectively, and the Latin word palustris, meaning ‘marshy’ (6). This refers to the bird’s habit of constantly moving around on or near the marsh floor (2) (3), foraging for prey low in the vegetation (3) (4).
The marsh wren’s diet is formed mostly of invertebrates (3) (4), including ants, wasps, beetles, and spiders (2) (3) (4). As well as searching along the marsh floor, the marsh wren also gleans prey items from the stems and leaves of cattails and other marsh vegetation, and may make brief sallies into the air to catch flying insects (3). Interestingly, this species is known to frequently damage, and sometimes eat, the eggs of other bird species as well as the eggs of other marsh wrens (3) (4).
Migrant marsh wrens typically arrive on their breeding grounds between late April and early June (5), with southern populations tending to breed earlier than those in the north (4). Individuals of this species often exhibit site fidelity between years, returning to their home marshes (5) where males display on territory borders by fluffing out their feathers and quivering their wings at other males (5). The marsh wren is a polygynous species, meaning that the males mate with more than one female during the breeding season (3) (4) (5).
The male marsh wren builds several nests in a breeding season (3) (4) (5), typically 5 or 6 but sometimes as many as 27 (5), before escorting potential mates around the site to inspect them (3) (4) (5). During these encounters, the male frequently bows low with his tail held high (3), and the female marsh wren typically selects a nest by adding layers and lining to the chosen one (3) (4) (5). Alternatively, the female may build a nest from scratch (3) (5).
The nest itself is a domed mass of grasses and sedges (2) (4) lined with fine leaves, feathers and small stems (3) (4), and can take up to eight days to complete (4). This structure is lashed to vegetation (2), and is typically placed about one metre above the water (4). A completed breeding nest can be identified by the presence of a side entrance hole (2) and a small, protruding shelf of lining material which prevents the eggs from rolling out (3) (4).
The female marsh wren usually lays a clutch of four to six eggs (3) (4) (5), although clutches can contain as few as three and as many as ten eggs (2) (3) (4). The timing of peak egg laying varies depending on the location, with most eggs being laid between early June and late July in New York state, and as early as late May in Illinois (3). Marsh wren eggs are dull, chocolate brown and are speckled with dark spots (2) (4) (5), particularly around the larger end (3). Only the female incubates the eggs (3) (4) (5), with incubation lasting between 12 (3) and 16 days (4). The male marsh wren’s involvement in caring for the young is variable across this species’ range (3) (4). The young marsh wrens typically fledge after about 13 to 15 days (3) (4), but may be fed by the adult birds for a further 2 weeks (3). Female marsh wrens are known to produce more than one brood per breeding season (3).