The Louisiana Waterthrush: Pennsylvania's Perfect Bio-indicator of Stream Quality
(By: Bob Mulvihill and Steve Hoffman)

The Louisiana Waterthrush, one of Pennsylvania's most engaging songbirds, has one primary ecological requirement: a healthy forested headwater stream with lots of aquatic macroinvertebrates. Deforestation, agricultural runoff, siltation and acid mine drainage negatively affect the water quality of these streams and the suitability of this habitat for nesting waterthrushes.

But, what is a waterthrush, anyway? And, for those of us who care about our drinking water, trout or bass fishing, or agricultural production associated with larger streams and rivers, why is the ecological health of a little stream and its effects on a small, seldom seen bird important? Read on!

The Louisiana Waterthrush is a common nesting bird throughout much of Pennsylvania, especially in the mountainous parts of the state, where it prefers medium- to high-gradient forested streams. Along these streams this little bird usually defends a narrow, linear territory ranging from 300-1,000 yards in length. The waterthrush is a brownish, streak-breasted little bird with a very loud, ringing song that can be heard from hundreds of yards away, even over the noise of a rushing stream! When it isn’t singing, waterthrushes often can be found walking over rocks and logs in the stream, searching for aquatic insects, rhythmically bobbing their tail.

Because first and second order streams (so-called headwater streams) comprise two-thirds or more of the total stream length in larger riparian ecosystems, stressors affecting them can have a cumulative negative effect on higher order streams and major river systems. Monitoring the condition of these small streams is an important component of any assessment of overall watershed health. Because they are so numerous within any large watershed, headwater streams can be a logistical and economic challenge to monitor. This is where employing the Louisiana Waterthrush as a bio-indicator may help.

Widespread surveys of waterthrushes along forested headwater streams throughout Pennsylvania could add a great deal of information about overall watershed health. For example, watersheds without waterthrushes (or with extremely low densities of waterthrushes) may be an indication of poor water quality.

Territorial male waterthrushes can be effectively surveyed from accessible points along small streams by listening for their early morning song (or by using tape song playback) from mid-April through the end of May. In addition, evidence of these birds can be gathered by searching for the telltale whitish splay (droppings) that the species habitually deposits on exposed rocks and logs in the stream.

In general, within any forested watershed, the higher the density of nesting waterthrushes the better is likely to be the watershed’s overall ecological health (or prospect for ecological recovery). Even if there are significant negative impacts acting directly on the larger order streams and rivers within a watershed, if that watershed drains an abundance of high quality headwater streams, it will have greater prospects for recovery, and for maintaining ecological health in the future. Conversely, correcting problems within the larger order streams in a watershed may be less successful if the condition of the watershed’s headwater streams is poor.

So, why not join Audubon Pennsylvania and begin making plans now to assess the headwater streams in your watershed based on this habitat’s keystone species, the Louisiana Waterthrush. For more information about the bird and this monitoring project visit our website, http://pa.audubon.org. Instructions and data sheets can be downloaded from this website, or you may call the Audubon office to request that forms be mailed to you.

A special waterthrush monitoring training session will be offered at the upcoming Third Annual Volunteer Statewide Water Monitoring Summit on February 22, 2003, in State College, at the Conference Center.

About the authors: Bob Mulvihill serves as the Field Ornithologist for Carnegie Natural History Museum's Powdermill Nature Reserve (near Ligonier, PA; Contact info: (724) 593-7521; e-mail: mulvipnr@westol.com). Steve Hoffman is Audubon Pennsylvania's Director of Bird Conservation, based in Harrisburg. (Contact info: (717) 213-6880; e-mail: shoffman@audubon.org).