Marsh Wren Cistothorus palustris This information was scanned from The Birds of British Columbia (Campbell et al.), Volume III, pages 329-334. Volumes I, II and III of The Birds of British Columbia can be ordered electronically at: orders@ubcpress.ubc.ca from UBC Press in Vancouver, British Columbia.

 

Range Breeds from southwestern, central, and northeastern British Columbia, northern Alberta, central Saskatchewan, and across much of southern Canada to New Brunswick, south to northeastern Baja California, the Gulf coast, and Florida. Winters along the coasts throughout its range, and in the interior from southern British Columbia south to the southern United States, Baja California, and mainland Mexico.

Status On the coast, fairly common to common resident in the Georgia Depression Ecoprovince; rare resident on Western Vancouver Island of the Coast and Mountains Ecoprovince; casual on the Southern Mainland Coast of that ecoprovince. Absent from the Queen Charlotte Islands. In the interior, uncommon resident and uncommon to fairly common migrant and summer visitant in the Southern Interior and the Southern Interior Mountains ecoprovinces; uncommon to fairly common migrant and summer visitant to the Central Interior Ecoprovince; accidental in early winter. Uncommon migrant and summer visitant in the Peace Lowland of the Boreal Plains Ecoprovince; very rare further north, in the Taiga Plains Ecoprovince; casual in the Sub-Boreal Interior Ecoprovince; accidental in the Northern Boreal Mountains Ecoprovince. Breeds.

Status Change In 1947, the Marsh Wren had not been recorded from areas north of Tachick Lake, near Vanderhoof. On Vancouver Island, it was noted at the same time as "Resident ... formerly at least, on southeastern Vancouver Island," suggesting that the Marsh Wren was not as common there as in the past (Munro and Cowan 1947). This wren is now locally but fairly abundantly distributed on southeastern Vancouver Island, and it now breeds in small numbers in northeastern British Columbia.

Nonbreeding The Marsh Wren has a local but widespread distribution across southern British Columbia, including southeastern Vancouver Island north to Campbell River, western Vancouver Island north to Tofino, the Fraser Lowland, the Okanagan, Nicola, and Thompson river valleys, the Thompson Plateau, the Creston valley and other southern regions of the west Kootenay, and the east Kootenay from Cranbrook north to Golden. Further north, it occurs locally in the Central Interior north to near Vanderhoof. Small populations occur east of the Rocky Mountains in the Peace Lowland and Fort Nelson Lowland. The Marsh Wren is absent from northern Vancouver Island, the Northern Mainland Coast and Queen Charlotte Islands of the Coast and Mountains, the Northern Boreal Mountains (except for a record from Atlin), and virtually all of the Sub-Boreal Interior (contrary to Godfrey 1986). The highest numbers in winter occur in the Georgia Depression, specifically the western edge of the Fraser River delta and the Saanich Peninsula. On Vancouver Island, few birds winter north of Nanaimo. Root (1988) states that areas of high concentrations of Marsh Wrens in winter occur where the minimum January temperature exceeds -4°C. Temperatures along the coastal fringe of the Fraser River delta frequently fall below this point, but only for brief periods. During nonbreeding seasons, the Marsh Wren occurs at low elevations from sea level to about 1,040 m. During winter on the coast, most birds frequent marshes at or near sea level. Important wintering sites include the tidal marshes of the Fraser River estuary, including Boundary Bay and the lower reaches of the Nicomekl and Serpentine rivers; the freshwater marshes of southeastern Vancouver Island from Victoria to Campbell River; and meadows and marshes at Tofino Inlet, on the west coast of Vancouver Island. In the Okanagan valley, there is a small wintering population along the valley floor, at about 300 m elevation, from Vernon south to Osoyoos Lake. The Marsh Wren is seldom found in any habitat except wetlands with emergent vegetation. On the coast, it occurs mainly in brackish marshes. In the interior, it prefers lacustrine and palustrine marshes with heavy stands of cattail. In all areas it can also be found in stands of bulrush, tall sedges, and mixed vegetation consisting of shrubs, forbs, rushes, and grasses along the slightly drier circumference of many marshes. The Marsh Wren also frequents dense thickets of hardback and sweet gale, typical littoral vegetation of many freshwater marshes on the coast. In the Georgia Depression, principally the western parts of the Fraser River delta and near Victoria, the Marsh Wren is fairly common through the winter. Numbers seem to increase there from February to April, which suggests a northward movement into the western Fraser Lowland and southeastern Vancouver Island from the coast of Washington state. Alternatively, this may simply reflect the beginning of the breeding season, when singing by males greatly enhances detectability. In the northern and eastern parts of the Fraser Lowland, there are no recent winter records of the Marsh Wren. This part of the population may move the short distance to the Fraser River delta or migrate out of the province. The winter status of this wren remains to be thoroughly investigated, however, and is difficult to determine because of its secretive nature during winter. In the interior, the Marsh Wren is mainly migratory except for small wintering populations in the Okanagan valley and possibly the Creston valley. In the Okanagan valley, spring migrants return in March and April (Cannings et al. 1987). Arrival in the valleys of the west and east Kootenay occurs mainly in April, and populations peak in May. In the Central Interior, early spring migrants can arrive after the first week of March, but the population peaks in May. In the Boreal Plains, spring migrants arrive in early May. The autumn migration of populations in the Taiga Plains and Boreal Plains occurs in August, and only a few birds remain as late as mid-September. In the Central Interior, the Marsh Wren moves southward in August and September, but small numbers remain until early October, and occasionally as late as November. Further south in the interior, most of the population leaves during September and October. The migration of the Marsh Wren from the interior of British Columbia apparently occurs entirely east of the coastal mountain ranges. There are no specimens of the interior subspecies from the coastal marshes of the Fraser River delta or Vancouver Island. In the Georgia Depression, an unknown portion of the population migrates southward in August and September, leaving a smaller wintering population. On the coast, the Marsh Wren has been recorded regularly throughout the year; in the interior, it is present regularly from 10 March to 20 October, except in the Okanagan valley, where it occurs regularly throughout the year.

Breeding Nests Eggs Nest Success The Marsh Wren has a localized breeding distribution throughout much of southern British Columbia. Generally, south of the latitude of Williams Lake, its known breeding distribution is similar to its nonbreeding distribution. However, breeding has not been confirmed on western Vancouver Island, Port Alberni, Campbell River, Squamish, or Golden. North of Williams Lake, there are 8 known nesting locations: Pantage Lake near Quesnel, Tachick Lake near Vanderhoof, Cranberry Marsh near Valemount, 4 sites from the Boreal Plains (McQueen Slough, Fort St. John, Boundary Lake, and Cecil Lake), and a site near Kotcho Lake in the Taiga Plains (Campbell and McNall 1982). The latter is this wren's northernmost breeding location in the province. In recent years, 1 or 2 adults and empty nests have been found in July at Parker Lake, near Fort Nelson. However, breeding (nests with eggs or young) has not been confirmed. The Marsh Wren reaches its highest numbers in summer in the Georgia Depression, specifically on the Fraser River delta and southeastern Vancouver Island. Breeding Bird Surveys for both coastal and interior routes for the period 1968 through 1993 contain insufficient data for analysis. The Marsh Wren nests in isolated pairs or in loose colonies, from near sea level to 60 m elevation on the coast and from 270 to 1,040 m elevation in the interior. All breeding records for British Columbia are from wetland habitats, mainly estuarine, lacustrine, and palustrine marshes. The wren's preferred habitat within these wetlands includes emergent beds of cattail, bulrush, and sedge, but some nesting territories are established where shrubs such as hardback, sweet gale, and willow predominate. Wet ditches with emergent vegetation also provide nesting habitat. Shrub habitats are used for nesting more frequently on the coast than in the interior.  On the coast, the Marsh Wren has been recorded breeding from 11 April to 30 June; in the interior, it has been recorded breeding from 31 March (calculated) to 22 August.

Nests:  Most nests (n = 124; 59% from coastal populations) were built in stands of cattail (51%), hardhack (23%), sedge (8%), and willow (6%). Other nest substrates included tall grass, red elderberry, sweet gale, salmonberry, and rushes. Nests were typically built over water and were attached to several stems of vegetation. The heights for 213 nests ranged from near water level to 2.4 m above the water, with 61% between 0.6 and 0.9 m above the water. Nests were elliptical structures constructed of strips of cattail, grasses, sedges, and other plant fibres, and frequently included large amounts of cattail down, willow fluff, or other very soft material. Some nests were constructed with large amounts of the water alga, Spiroggra sp. (Munro 1943c). The nest lining is predominantly cattail down, but plant fibres, fine grass, feathers (Munro 1942), moss, and hair are often included. Munro (1945a) states that in the Cariboo, the "roundstem" bulrush was the most commonly used nesting material but that local populations differed in nest materials used. A population at Westwick Lake used duck feathers extensively; at Lac la Hache and Horse Lake, most wrens made their nests of flat sedges woven around willow branches. During the courtship period, males may build several "dummy" nests within their territories. These nests are not lined with soft materials; lining is added by the female only to the chosen nest Werner 1963). Dummy nests have been shown to have adaptive importance, in that active nests built near larger numbers of dummy nests were more successful than those near fewer dummy nests (Leonard and Picman 1987b) (see REMARKS). At Pitt Meadows, Runyan (1979) found dummy nests as early as 14 March and lined nests ready for use on 13 April, with the first eggs 6 days later. In his study area, simultaneously active nests reached a density of 2.6/ha. Nests were placed about 93 cm above ground or water, in vegetation 157 cm in height. Nests averaged 8.2 m from the water's edge over water 6.3 cm deep. Forty-three percent of the nests were built over land. Eggs: Dates for 202 clutches ranged from 4April to 31 July, with 53% recorded between 11 May and 13 June. Calculated dates indicate that eggs can be laid as early as 31 March and can hatch as late as 6 August. Sizes of 175 clutches ranged from 1 to 8 eggs (lE-17, 2E-14, 3E-12, 4E-33, 5E-56, 6E-27, 7E-9, 8E-7), with 51% having 4 or 5 eggs. The incubation period is 12 to 16 days (Verner 1965; Ehrlich et al. 1988), and is longest early in the season (Verner 1963). Incubation begins before the clutch is complete, and eggs hatch asynchronously, with a spread of 1 to 3 days between hatching of first and last eggs (Verner 1965). Nest Success: Insufficient data for analysis. Young: Dates for 57 broods ranged from 1 May to 22 August, with 52% recorded between 29 May and 20 June. Calculated dates indicate that young may occur as early as 21 April. Sizes of 33 broods ranged from 1 to 7 young (1Y-4, 2Y-4, 3Y-8, 4Y-6, 5Y-7, 6Y-3, 7Y-1), with 64% having 3 to 5 young. The nestling period is 13 to 16 days (Ehrlich et al. 1988). The extent of double-brooding in British Columbia is unknown, but it may occur frequently. In Washington, most pairs raised 2 broods (Verner 1963). For pairs that raised 2 broods, the elapsed time between the beginning of the first clutch and the beginning of the second clutch ranged from 44 to 51 days, with a mean of 47 days. In Ontario, Peck and James (1987) suggest that some pairs raise 3 broods annually. Brown-headed Cowbird Parasitism: In British Columbia, there were no cases of cowbird parasitism in our sample of 219 nests found with eggs or young. However, Picman (1986) examined 1,200 Marsh Wren nests at Westham Island, Delta, and found 1 nest with 2 broken Marsh Wren eggs and a cold, undamaged cowbird egg. This record is the first documented case of attempted cowbird parasitism of the Marsh Wren in North America.

Remarks Two subspecies of the Marsh Wren are present in British Columbia (American Ornithologists' Union 1957): C. p. paludicola occurs on the coast and C. p. plesius occurs in the interior. Although we know of no specimens from northeastern British Columbia, it is probable that populations in the Boreal Plains and Taiga Plains belong to the subspecies C. p. iliacus, which occurs in Alberta. In the decade between 1965 and 1975, the breeding range of the Marsh Wren in Alberta expanded northward (Salt and Salt 1966,1976), and this may account for the fairly recent expansion of the species into northeastern British Columbia. Marsh Wrens often destroy the eggs of neighbouring wrens or blackbirds. Picman (1977, 1980a, 1980b, 1984) studied the aggressive interaction between Marsh Wrens and between the wrens and Red-winged Blackbirds. He concluded that nest destruction by aggressive Marsh Wrens helps exclude other members of the same species and other small, marsh-nesting songbirds. Leonard and Picman (1986) showed that, in Manitoba, wren nesting territories increased in size when blackbirds were removed. In the western United States, Bump (1986) found that Marsh Wrens destroyed or disrupted 5.3% (n = 189) of nesting attempts by Yellow-headed Blackbirds. Gutzwiller and Anderson (1987) discuss 4 habitat variables that they use in their model to characterize the suitability of a wetland for supplying cover and reproductive needs for Marsh Wrens. These include growth form of emergent hydrophytes, percent canopy cover of emergent herbaceous vegetation, mean water depth, and percent canopy cover of woody vegetation. In British Columbia, more young were fledged at a site with denser vegetation and deeper water than at a site with less vegetation and shallower water (Leonard and Picman 1987a). The Marsh Wren was formerly known as the Long-billed Marsh-Wren.