Parkesia motacilla (Vieillot, 1809)
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Basis for Listing
The Louisiana waterthrush breeds throughout much of the eastern United States, and in southern Ontario, Canada. Louisiana waterthrushes are very uncommon in Minnesota, primarily occurring in two regions. In southeastern Minnesota, the species is most frequently found along swiftly flowing streams in forested, steep-sided valleys. In east-central Minnesota, they are largely associated with the St. Croix River and its tributaries. In general, the St. Croix is a larger river, flowing through more level terrain than streams in southeastern Minnesota. Because the Louisiana waterthrush requires mature forest in riparian areas, it is sensitive to disturbance of forest cover and streambeds and associated microhabitat features, as well as water quality.
Two species of waterthrush occur in Minnesota, both with brown upperparts, whitish underparts with dark streaks, prominent white eyebrow stripes, and tail-wagging behavior. The Louisiana waterthrush is best distinguished from the similar northern waterthrush (Seiurus noveboracensis) by its loud, distinctive song consisting of 2-3 clear, slurred whistles followed by a rapid jumble of notes. Physical differences between the two waterthrushes are subtle. In general, the Louisiana waterthrush has a slightly longer bill, a wider, whiter eyestripe that broadens behind the eye, brighter pink legs, and buffier flanks. In addition, the Louisiana waterthrush has an unstreaked throat, as opposed to the streaked throat of the northern waterthrush. This latter feature is quite variable however, and some northern waterthrush have a largely unstreaked throat. During the breeding season, there is little overlap in the distribution of the two waterthrush species, except in the upper reaches of the St. Croix River in northern Chisago and Pine counties.
The Louisiana waterthrush is almost exclusively found in mature riparian forests. Typical habitat consists of steep-sided valleys with swiftly flowing streams that have rocky stream beds and riffles (Robinson 1995). In southeastern Minnesota, Louisiana waterthrushes are most frequently found in this typical habitat. In this region, important microhabitat features such as small hollows or cavities within eroded stream banks, or exposed root masses immediately adjacent to streams, may be used as potential nest sites. Other crucial habitat components include adequate foraging sites of exposed/emergent rocks at the edge of water or within a stream; submerged leaf litter; and areas of water less than 3-5 cm (1.2-2.0 in.) deep (Stucker 2000). Many of the Louisiana waterthrushes along the St. Croix River occur along small streams flowing through steep-sided ravines, as well as in seepage areas at the bases of steep slopes (Eliason and Fall 1989). However, a significant number of Louisiana waterthrushes occur in level, silver maple floodplain forest, particularly along the Kettle River, in Pine County. These floodplain areas are characterized by small channels with slow-moving water.
Biology / Life History
The Louisiana waterthrush winters in Central America and the West Indies. In Minnesota, Louisiana waterthrushes return to breeding areas in mid-April, and nesting activities are well underway by early May. This is one of the earliest nesting warblers in the state, and consequently it has probably been overlooked in many areas because singing activity has largely ceased by late May and June, when most breeding bird surveys are conducted. In breeding areas, Louisiana waterthrushes occupy well-defended breeding territories. Their linear territories follow a stream bed and can vary regionally from 400-900 m (1,312-2,953 ft.) in length (Robinson 1995). The Louisiana waterthrush typically builds its nests in small hollows or cavities within the root mass of upturned trees, within the bank or stream side, or under fallen logs. The female lays an average of 5 eggs, which hatch after 13 days. The young fledge approximately 9 days after hatching. Major food items are aquatic invertebrates.
Conservation / Management
Louisiana waterthrushes require mature deciduous forest adjacent to streams. In southeastern Minnesota most stream valleys have been disturbed by grazing, logging, and/or cultivation. Stream valleys with insufficient canopy cover (less than 80%-90%), and a resultant dense herbaceous layer dominated by graminoids or weedy forbs, are unsuitable for this species. Management considerations for Louisiana waterthrush habitat in southeastern Minnesota include maintaining mature stream-side forests, providing or maintaining nesting habitat in steep, eroding stream banks, and increasing riffle areas and shallow stream edges (Stucker 2000). Louisiana waterthrushes also require relatively large tracts of forest. Although the minimum width of forest corridors necessary for waterthrushes is unknown, a suggested buffer of 100 m (328 ft.) should be protected around the species' core riparian habitat (NatureServe 2008). Other potential threats to Louisiana waterthrushes include stream siltation and poor water quality due to agricultural runoff or other sources. Even though brood parasitism by brown-headed cowbirds in southeastern Minnesota is at the low end of reported rates for the Louisiana waterthrush, it still remains a conservation concern (Stucker 2000). When habitat management for trout is proposed in occupied or high quality Louisiana waterthrush habitat, care should be taken to maintain microhabitat elements important to this rare species.
Conservation Efforts in Minnesota
Breeding bird surveys by the Minnesota Biological Survey and research in southeastern Minnesota have greatly increased our knowledge of the distribution, habitat use, ecology, and management of Louisiana waterthrushes in Minnesota. Stucker (2000) identified microhabitat features important to this species, and investigated the effects of trout habitat improvement on waterthrushes in southeastern Minnesota. Because a vast majority of Louisiana waterthrushes in southeastern Minnesota occur along designated trout steams, trout stream restoration can affect waterthrush populations. If habitat improvement projects for trout in poor waterthrush habitat include considerations for waterthrush nesting and feeding areas, they can actually benefit waterthrush populations.