Introduction

Louisiana Waterthrush, South Padre Island, TX, April.

Figure 1. Distribution of the Louisiana Waterthrush.

The Louisiana Waterthrush compensates for its cryptic, thrush-like plumage with a loud, ringing, resonant song, usually loud enough to carry long distances over the continual background noise of rushing water that characterizes this species’ streamside habitat. Breeders forage primarily on the ground alongside forested headwater streams; during migration and winter, individuals often forage away from forested wetlands, along flooded roads or trails, impoundments, and even in parks, lawns, and gardens. Throughout its range this species is noted for constantly wagging its tail in a teetering motion as it walks along the ground. In fact, the habit is so pronounced that both the genus and species name mean “tail-wagger.” One of the earliest wood-warblers to arrive on its breeding grounds each spring in the eastern United States and southern Canada, the Louisiana Waterthrush is also one of the earliest to depart after breeding for its wintering grounds in Central America and the West Indies.

Focused studies of the Louisiana Waterthrush began with detailed natural history accounts of breeding individuals by Eaton (1958) near Ithaca, NY. Later, Craig (1984, 1985, 1987) reported results of comparative foraging studies between Louisiana and Northern waterthrush during the breeding season in Connecticut. George (2004) and Master et al. (2005) found this species to be widespread and moderately common on wintering grounds in Costa Rica, in habitat nearly identical to that preferred on its breeding grounds.

Impacts of human land use on water quality during much of the 20th century spurred interest in developing biological indicators, including benthic macroinvertebrates and birds that consume them. Stucker (2000) studied this species in se. Minnesota and found that stream reaches where birds were detected had a greater proportion of pollution-sensitive benthic macroinvertebrate taxa than along reaches where birds were not detected. Results from sw. Pennsylvania demonstrated that waterthrush territory densities were lower and that laying dates were advanced along streams impacted by acid mine drainage, compared to circumneutral streams Mulvihill (1999, 2008). Another four-year study in the Georgia Piedmont reported that some indices of benthic macroinvertebrate integrity were elevated where waterthrushes were present compared to where they were absent (Mattssson and Cooper 2006). Another finding from the Georgia Piedmont study indicated that waterthrush reproduction was greatest during periods of intermediate rainfall levels (Mattsson and Cooper 2009). Together, these findings indicate that measures of Louisiana Waterthrush distribution and reproduction may be useful as indicators of stream ecosystem integrity. A long-term monitoring program that began in 2007 incorporates measures of Louisiana Waterthrush distribution as vital signs of watershed condition in the Eastern Rivers and Mountains Network of the National Park Service (BM).