Sedge Wren (Cistothorus platensis) Brian Johnson
Iron Co., MI 6/18/2005 © Elizabeth Rogers
(Click to view a comparison of Atlas I to II)
Diminutive in stature and seemingly loathe to and South Dakota across Minnesota and Wisconsin to Lake Michigan (Sauer et al. 2008). fly, and then doing so in a laborious and fluttering fashion, the sprightly Sedge Wren is a Distribution rather secretive bird that generally keeps As shown by both Michigan atlases, Sedge frustratingly out of view in lush vegetation. Wrens range widely across both peninsulas, However, the species boasts a belligerent and though much of the NLP is relatively sparsely energetic demeanor typical to other wrens, and populated. Only two counties lacked records it is very aggressive towards conspecifics and during MBBA II (six during MBBA I). The other grassland birds. Males sometimes eastern SLP and large areas of the UP were simultaneously mate with two females poorly represented during MBBA I, but the (Crawford 1977, Burns 1982), and both sexes species was distributed much more evenly destroy the eggs of other Sedge Wrens and other during MBBA II. On a local level, populations species breeding nearby (Picman and Picman demonstrate high motility and low site fidelity. 1980). Although males usually sing from low, semi-concealed perches, they do so persistently, As its name reflects, the species is highly not only continuing later in the day than several dependent on dense mats of tall, usually course- other species, but their harsh, staccato rattle is bladed grasses and sedges. Moist or frequently uttered during all hours of the night ephemerally wet situations are another key (and sometimes in a vigorous banter with their requirement, and Sedge Wrens typically avoid neighbors). arid soils even if the grass grows densely.
Although they favor larger, contiguous habitats, Although various non-migratory subspecies area constraints are less important than reside in Central and South America, the single appropriate vegetative conditions (Dechant et al. subspecies occurring north of Mexico breeds in 2002). Appropriate natural environments southern Canada and the northern U.S., from include meadows and bogs, former beaver Alberta east to Vermont and south to southern impoundments, fens, and the periphery of lakes Illinois, with scattered records further east and and marshes, but Sedge Wrens eschew cattail south (Herkert et al. 2001). The highest stands and deeper water favored by the Marsh densities occur from Manitoba and central North Wren. A variety of native and exotic grasses are tolerated, and human-altered sites, such as
© 2011 Kalamazoo Nature Center Sedge Wren (Cistothorus platensis) Brian Johnson hayfields, pastures, and fallow farmland, Survey records published in Jack-Pine Warbler provide suitable habitat. The species is tolerant and Michigan Birds and Natural History, most of scattered shrubs, but it avoids heavy woody depart the state from early September to mid- cover. Habitat associates across most of October. Michigan include Swamp Sparrow, Wilson's Snipe, Savannah Sparrow, and Bobolink. In the Abundance and Population Trends UP, Le Conte's Sparrow is a regular cohort, (Click to view trends from the BBS) while Willow Flycatcher and Henslow’s Sedge Wrens readily colonize or vacate areas as Sparrow often occur within their home ranges conditions dictate (Kroodsma and Verner 1978). downstate. Seasonal precipitation in particular, has a dramatic effect on the suitability of nesting Breeding Biology areas, and as a result, Sedge Wrens may occupy Sedge Wrens tend to exhibit a staggered arrival certain areas in some years and be entirely chronology and a prolonged breeding season. absent in others. But even when suitable habitat The earliest arrivals appear in the LP at the end persists, site fidelity still may be very low. At of April, but most establish breeding territories Munuscong, none of the 25 birds banded in during the second half of May. At Munuscong 2006 and 2007 appeared during the subsequent WMA in the eastern UP, solitary or scattered years (B. Johnson, unpubl. data). Densities, males arrive around the end of the first week of however, can be very high. In 1934, up to 35 or May. Several more appear during the last ten 40 were singing simultaneously in a 10-acre days of the month, at which time females also Calhoun County marsh (Walkinshaw 1935). appear, but additional arrivals continue to establish territories into late June (B. Johnson, The confounding effects of patchy distributions, unpubl. data). Walkinshaw (1935) located eight irregular patterns of arrival, and population nests in June, but he found two in August and shifts from year to year make discerning Sedge figured the overall season extended from May to Wren population trends difficult. While September. At Munuscong, fledglings appear at populations have almost certainly diminished the end of June, but breeding continues into with the historical loss of grassland ecosystems, August (B. Johnson, unpubl. data). As testament numbers appear fairly stable in existing regions to the furtive habits of this species, breeding of appropriate habitat. On a continental level, Sedge Wrens were confirmed from only 17 of BBS data has indicated a slight increase of 1.5% 399 townships in MBBA I. This confirmation annually from 1966 to 2007 and a 1.3% annual rate (4.3%) was one of the lowest from that increase (with less reliability) from 1983 to effort, and the figure from MBBA II was 2007 (Sauer et al. 2008). While imprecise, essentially the same. Christmas Bird Count trends, adjusted for birds per party-hour, also revealed an increase over Continuing later than most other grassland the same time frame (NAS 2009). birds, Sedge Wrens regularly sing into the first part of August at Munuscong (pers. obs.), and In Michigan, the species has been encountered Walkinshaw heard them singing during on 30 BBS routes since 1983, which indicates a September and October, including at least five wide distribution, but with an average of less near Battle Creek on 22 October 1933 than one bird per route, the species occurs (Walkinshaw 1935). However, when they cease infrequently. Statewide BBS data reveals a non- vocalizing, Sedge Wrens become difficult to significant decrease since 1966 and a non- find, so post-breeding activities are not well significant positive trend since MBBA I (Sauer documented. According to Michigan Bird et al. 2008), but the paucity of detections places
© 2011 Kalamazoo Nature Center Sedge Wren (Cistothorus platensis) Brian Johnson considerable doubt on these figures. During landowners also offers key benefits for the long- MBBA II, Sedge Wrens were found in a term security of this species. A substantial somewhat larger number of townships (7%), but proportion of Sedge Wrens nest later in the some of those gains may correlate to greater season than other grassland species, so those observer effort. Increases were noted in all three that reside in hayfields are vulnerable to zones, with the UP showing the largest gain, mowing. To reduce losses, harvesting could be albeit concordant with an increase in coverage. postponed until as late as possible, or Whether corroborating poor site philopatry or considering the small territories occupied by indicating habitat changes, 181 of the 400 Sedge Wrens, the wettest parcels of the field townships having Sedge Wrens during MBBA I could be left unmowed. Landowner incentives, (48 UP, 46 NLP, 87 SLP) also had them during such as the CRP program, can provide MBBA II. Partners In Flight estimates the additional habitat for this and other grassland Michigan population at 43,000 birds, or about species (Dechant et al. 2002). 0.7% of the total north of Mexico (PIF 2007).
Conservation Needs While adverse climatological effects (i.e. moisture conditions) may temporarily constrain population sizes, land practices that contribute to the continued loss and degradation of wet grasslands have a pronounced bearing on Sedge Wren viability. On a local or short-term scale, the effects of habitat alteration are probably minimal, since the species can readily shift to alternate breeding sites. However, sweeping changes, such as land conversion, wetland drainage, extended droughts, and plant succession, place severe restrictions on Sedge Wren densities.
Due to the relatively low numbers of Sedge Wrens and the scarcity of favored habitat, policies and practices that promote and preserve grasslands are vital for the conservation of this species. Relevant preserves and refuges should be managed to curtail the effects of succession and invasive plants, since uncontrolled woody encroachment will degrade nesting habitat within a few years. Periodic disturbances like grazing, mowing, and prescribed burning can be used to control woody and invasive plants and subsequently foster luxuriant growth of grasses and sedges.
Because the species readily uses hayfields and fallow fields, cooperation with private
© 2011 Kalamazoo Nature Center Sedge Wren (Cistothorus platensis) Brian Johnson
Literature Cited Suggested Citation
Burns, J.T. 1982. Nests, territories, and Johnson, B. 2011. Sedge Wren (Cistothorus reproduction of Sedge Wrens (Cistothorus platensis). In Chartier, A.T., J.J. Baldy, and platensis). Wilson Bulletin 94(3): 338-349. J.M. Brenneman (eds.). 2010-2011. The Crawford, R.D. 1977. Polygynous breeding of Second Michigan Breeding Bird Atlas. Short-billed Marsh Wrens. Auk 94: 359– Kalamazoo Nature Center. Kalamazoo, MI. 362. Accessed online at:
© 2011 Kalamazoo Nature Center