Sometime in early April, I hear the ringing song of a Louisiana waterthrush near our Plummer’s Hollow stream. One of the first neotropical migrant birds to return, he comes winging in from as far south as northern South America and southern Cuba.
This handsome brown warbler, his whitish breast streaked with brown, looks more like a thrush than a warbler. Along with his congener, the northern waterthrush, the Louisiana waterthrush wades on long, pink legs in streams and bobs his tail and rear like a spotted sandpiper.
I spend a lot of time along our mile-and-a-half, first order stream, watching and listening to these fascinating birds. By mid-April there are usually four males staked out along the stream singing, defending their long, narrow territories and courting the returning females. It’s important to catch their singing early, though, because as soon as they pair up, the males slow down and almost stop singing.
A favorite place for waterthrushes is below our Waterthrush Bench, and last spring their activity was especially interesting. On April 18 I watched two singing waterthrushes bobbing their tails as each one tried to stay above the other when they landed on mossy logs, tree branches, and in the stream itself. They moved several hundred feet upstream before flying back down stream, and I wondered if they were two males in a territorial dispute or a pair involved in a courtship ritual.
The last day of April, as I sat on Waterthrush Bench, I watched a waterthrush as it poked about in the puddles of a backwater, pulling aside rotted leaves in what ornithologists call ”leaf pulls” as it searched for food. Although 89 to 98% of waterthrush feeding consists of quick, jab-like strokes called “picks,” “leaf pull” is an alternate strategy. In both cases, they are searching for aquatic insects and invertebrates. According to one study in northeastern Connecticut, before the leaves emerge waterthrushes engaged in “leaf pull” 42% of the time and “picks” 54%, but “leaf pulls” decreased and “picks” increased as their breeding season progressed and trees leafed out.
After my waterthrush stopped “leaf-pull,” it waded about belly-deep in the water. Then it flew up on a moss-covered log spanning the backwater to preen. All the while it preened its breast, neck, belly and under its tail, that tail kept pumping as regularly as a metronome.
Years ago, again on the last day of April, in the deepest part of the hollow, which is overhung with hemlock and beech trees, I walked quietly downstream and saw a pair of Louisiana waterthrushes in the water in front of me. They didn’t notice me when they turned over wet leaves in the stream. As I followed and watched, the male walked a couple yards behind the female. Unlike most warbler species, the male and female look alike, so I was relying on a description of this courtship tactic by ornithologists. The male made a “zizzing” sound and fed the female. Then they continued alternately foraging and poking at the stream bank. After I followed them for fifteen minutes, they suddenly saw me, chipped warning notes, and flew off.
Last spring, on the fourth of May, a Louisiana waterthrush swayed and scolded on a branch overhanging the road near Waterthrush Bench. Somewhere nearby in the road or stream bank there must have been a nest with eggs. I remembered my son Steve’s discovery a quarter of a century ago of a nest he found in the road bank as he walked up the road. The female flushed in front of him and performed her broken wing act. Following his description, I easily found the nest four feet from the ground, tucked in over a rock well-padded with dead leaves. An overturned sapling provided a roof above the five whitish eggs spotted with irregular brown spots that lay in a nest of dried grasses.
The nest had been built on the south side of the ravine by both parents. They dug a shallow cup in the bank’s soil and hauled in fallen leaves from the forest floor to fill the cup and provide a short pathway to the nest, a task that ornithologists say takes three to four days. Incubation by the female lasts 12 to 14 days and the altricial nestlings go from naked to fully feathered in nine or 10 days when they fledge. The nest Steve found did produce not only nestlings but fledglings, and I saw both the nestlings and their fledging.
Since then, we’ve never found another nest but suspect that most are along the stream bank and in the interstices of uprooted trees, which are the usual nesting places for Louisiana waterthrushes.
The bird that scolded me last May then waded into the stream and poked up food from the wet moss on the rocks or from the swiftly-flowing water. Like the dippers of the western United States, Louisiana waterthrushes are wedded to clean, running streams. It jabbed quietly in the crevices, living its enviable life in the moving water whose babble blocks out all other sounds.
Its affinity for water makes it an ideal species to use when assessing the ecological health of streams, researchers discovered at the Powdermill Nature Reserve in southwestern Pennsylvania. This biological field research station of the Carnegie Museum of Natural History in Pittsburgh is best known for its long-running, year-round, bird-banding program begun in 1961 by Robert Leberman.
Leberman’s assistant, Robert Mulvihill, now at the National Aviary in Pittsburgh, along with Leberman, chose the Louisiana Waterthrush as a model for looking at bird populations back in 1996. After all, two streams — Powdermill Run and Laurel Run — hosted Louisiana waterthrushes. But those two streams differed in one important aspect. Powdermill Run’s water has a neutral pH of 7, but Laurel Run’s was an acidic pH of 5, the result of acid mine drainage from a small, hand-dug coal mine on nearby private land.
More than 50 years after this 30-year-long disturbance, it still impacts Laurel Run despite the best efforts of a local watershed association that installed a Successive Alkalinity Producing System to filter water through organic material and limestone into a settling pond to lower the acidity and remove heavy metals, as well as an attempt by the Department of Environmental Protection, using bioremediation techniques, to further improve stream quality.
Consequently, Louisiana waterthrushes breed early and abundantly on Powdermill Run and late and sparsely on Laurel Run because of the lack of macroinvertebrates, especially caddisflies and mayflies, in the acidic Laurel Run. In fact, by 2009, no waterthrushes bred on Laurel Run, yet over the more than ten years of monitoring, Powdermill Run remains a hot bed of successful, breeding waterthrushes. Apparently, the availability of the proper food — namely macroinvertebrates that favor clean water — is very important for attracting breeding Louisiana waterthrushes.
This study also made some natural history discoveries about Louisiana waterthrushes, according to Mulvihill, who directed the research. The males of this supposedly single-brooded, monogamous species occasionally engage in opportunistic polygyny, defined as pairing with two females at the same time. Eight times during the study, waterthrush pairs re-nested or double brooded after their first successful fledging of young. One female that started out on Laurel Run in her first year of breeding, transferred to Powdermill Run and brought off successful families for at least eight years.
Today, Steven Latta, Director of Conservation and Field Research at the National Aviary, continues Louisiana waterthrush research, studying one of its wintering grounds in the Dominican Republic. He’s especially interested in how water quality there affects the survival of the birds and whether or not they return to their breeding grounds. He also wants to use the species to understand what affects neotropical bird populations throughout the year. He writes, in a recent article in Birding, that “in addition to acidification, breeding success is likely linked to sedimentation and other forms of stream contamination, combined with the loss of surrounding vegetative cover in the riparian corridor… Preliminary results suggest that older, more mature forests with relatively high canopy cover, coupled with perennial streams that do not run dry in mid-summer droughts, are key drivers to reproductive success for such bird species.”
Back at Powdermill, scientists are now concerned about the impacts of natural gas drilling on water quality, macroinvertebrates and Louisiana waterthrushes. And they have joined other ornithologists in the state to study the affects of hydraulic fracturing on streams throughout Pennsylvania. They hope that birders will help by counting waterthrushes along streams and reporting their numbers to their local watershed association. Two territories per kilometer are considered a healthy number of waterthrushes along a stream.
Louisiana and northern waterthrushes were once lumped along with ovenbirds into the genus Sieurus, which means “to shake or move the tail,” but for decades Dr. Kenneth C. Parkes, the late curator of birds at the Carnegie Museum of Natural History, argued that the waterthrushes should be separated from ovenbirds. They differ too much in behavior, singing, structure, the way they move, their juvenile plumage and how long they keep it, as well as other differences that only ornithologists could sort out.
It took a Ph.D student in the Molecular Systematics Laboratory at the Swedish Museum of Natural History in Stockholm, George Sangster, who admired Parkes’s work, to prove his point. Using genetic analyses, he discovered that ovenbirds were only distantly related to waterthrushes.
On the strength of his work, the North American Classification Committee of the American Ornithologist’s Union agreed to put the waterthrushes in their own genus. Furthermore, they accepted Sangster’s name — Parkesia — in honor of Kenneth C. Parkes because of “his lasting contributions to avian taxonomy, molt terminology, hybridization and faunistics.”
Sangster finished his manuscript about his discovery in the Bulletin of the British Ornithologists’ Club in late July of 2007 and “hoped to inform Dr. Parkes about my intention of naming a genus after him,” Sangster told Paul Hess who wrote about this in PSO Pileated, The Newsletter of the Pennsylvania Society for Ornithology. “It was when I looked on the Internet for a contacting address that I found out that he had passed away only a week before.”
Only three other Pennsylvanians have been honored with a bird genus — William Bartram, Thomas Say, and Alexander Wilson. All of them lived and worked in the late eighteenth and early nineteenth centuries, and all were residents of Philadelphia.
How sad that Parkes never knew of his genus. But how serendipitous that one of the species Leberman and Mulvihill decided to study at Powdermill has not only become important in stream ecology but also honors a fellow western Pennsylvanian who, like them, devoted his life to the study of birds.