Of Willows and Willow Flycatchers
Fitz-bew! This year I didn’t hear the familiar bird song until mid-May. I was checking up on a riparian forest buffer site which I am always delighted to visit. The landowner is enthusiastic, generous, and a great steward, and had recently enrolled in the Alliance’s buffer program to reforest a wet pasture that is intersected by a small creek. Part of the magic of this site is that it holds a very successful riparian forest buffer that was planted through CREP around 17 years ago. You don’t always see high survival rates for riparian reforestation projects, especially ones that were planted back then, before establishment techniques were perfected. As I walked between the freshly planted trees and the burgeoning riparian forest, pride and hope swelling in my chest, that buzzy little song hit my ears and instantly transported me in time and space, to 2009 and of all places…the Mojave Desert in Nevada.
I had been hired as a field crew member by an environmental consulting company for the summer between my sophomore and junior years of college. It was an amazing opportunity, not only to add work with a second endangered species to my resume, but to see the American southwest; until that point I hadn’t been further east than the Blue Ridge Mountains in Virginia. My summer was to revolve around the Southwestern Willow Flycatcher (Empidonax traillii extimus), a small, drab songbird most infamous for being impossible to distinguish from other closely related flycatcher species without hearing its song: a simple two-note Fitz-bew! I knew nothing about this songbird, nothing about southwestern ecosystems, and honestly still very little about wildlife biology. I also had no idea how significant these four months in the desert would be for my career, worldview, and fundamental understanding of ecology.
The Willow Flycatcher is somewhat common across most of its breeding range, which covers the northeastern, midwestern, and northwestern US. As its name suggests, it is a denizen of woody thickets in wet areas, and seems to be especially fond of dense willow cover. Here in the east I exclusively find them in palustrine wetlands and riparian zones that have dense pockets of shrubs and small trees. In the southwestern US the habitat is largely the same, but wetlands and floodplains are largely under duress due to mankind’s tight control of water in the face of increasing scarcity. The Southwestern Willow Flycatcher subspecies is federally endangered, and has declined in step with the estimated 90% loss of its riparian habitat.
My role in 2009 was to locate and monitor Southwestern Willow Flycatcher (affectionately abbreviated SWIFL, which is pronounced as “swiffle”) territories and nests in the Muddy River and Virgin River watersheds, which empty into Lake Meade. I dutifully scoured every corner of our sites, and over the course of the summer began to see trends in habitat and flycatcher occurrence.
Most of the riparian zones in our sites (and essentially everywhere else I traveled in the southwest) were dominated by tamarisk (also called salt-cedar), a handful of introduced invasive species in the Tamarix genus. Tamarisk in an unequivocally nasty plant. Its branches are pliable yet nearly unbreakable, and it grows in such dense thickets that the only way to move through an infested area is often to army-crawl and wriggle through the sea of stems. It excretes salt from its leaves in a sticky, sooty, black, tar-like substance that coats anything it touches, and prolifically generates dandelion-like seeds, replete with a fluffy tuft that carries the seeds far on wind and water. By the end of a day’s work, we were often coated in soot that then affixed thousands of seeds.
Tamarisk is reviled not only by biologists who must move through thickets, but by many residents of the southwest because it drastically alters areas that it takes over. And in the desert, being a potential threat to water supply will not engender affection. It is more tolerant of salt and drought than native riparian species, which gives it a huge competitive advantage against the native plants in river systems that are now highly altered by humans. Historically, floodplains in the southwest would, well, flood, particularly in the spring when melting snow in distant mountains would feed raging rivers in the lowlands. The damming and regulation of southwestern rivers means that floodplains are far less likely to receive annual floods, so riparian soils stay dry and the salt exuded from tamarisk doesn’t get flushed away. Tamarisk readily germinates and flourishes in dry, salty soils, while native trees and shrubs fail to regenerate in these altered conditions. Additionally, cattle avoid eating tamarisk but relish the native riparian trees and shrubs. Stream systems that are both dammed and grazed are likely to become little more than tamarisk barrens in short order. And once they are dominated by tamarisk, they are unlikely to return to their diverse, lush natural states without immense intervention. Burning, herbicide, and manual pulling may slow down individual plants, but until the floodplain hydrology is restored, nothing else will be able to grow on hard, desiccated tamarisk-dominated soil.
Among the expanse of salt-cedar, there were occasional patches of native vegetation in the wettest areas, dominated by Fremont cottonwood (Populus fremontii), Gooding’s willow (Salix gooddingii), and coyote willow (Salix exigua, whose eastern subspecies is often called sandbar willow). This is where the SWIFLs went wild. We would occasionally find them singing and nesting in tamarisk shrubs, but the songbirds were dramatically more abundant and had more successful nesting attempts in the native patches than in the salt-cedar doldrums.
It took me until my second season with the sweet SWIFL, in 2011, to realize that the human-altered flood regime was encouraging the tamarisk takeover of our river systems. But it took five more years for me to understand precisely why the SWIFLs couldn’t persist in a world of tamarisk alone. I was back home in the mid-Atlantic as a full-blown conservation professional, learning more about pollinator conservation, when I read that willow trees were incredibly important insect food sources because they can be eaten by a broad array of species. I remember the precise moment, because it’s when the big picture immediately snapped into place. Most bugs, like cattle, won’t eat tamarisk. So the sprawling sea of tamarisk seemed so quiet and still because it was. The Willow Flycatchers needed their native cottonwood-willow communities not because they were picky, but because there wasn’t sufficient food anywhere else. Furthermore, most native insects can only eat a narrow range of native plants, so the less native plants we have in an area, the less insect biomass we will have, which almost always means less of all other fauna.
Think of the landscape you spend most of your time in. If it’s mostly developed or agricultural, there are likely few native plants around, at least relative to what would occur naturally. And our natural areas are increasingly altered by invasive plants here in the east too, so the forests that we do have are less suited to host a plentiful and sprawling food web of critters big and small.
Our mid-Atlantic floodplains are beset by many introduced invasive plants too, especially reed canarygrass (Phalaris arundinacea). Introduced to provide livestock forage in wet fields, it now strangles floodplains under a monocultural blanket of incredibly dense grass. If an area is dominated by reed canarygrass, it is highly unlikely that it will naturally regenerate into a forest. So it will forever hold low potential as habitat for native critters, whereas a floodplain dominated by native vegetation can host exceptionally diverse and abundant wildlife populations. Beyond limiting the food available for terrestrial fauna, reed canarygrass harms the streams that it grows along as well. Its fibrous roots collect sediment, leading to the narrowing of stream channels. Narrower channels means less habitat for aquatic lifeforms, and less interplay between the stream and the floodplain, a natural process that supports our riparian ecosystems here as much as it does in the southwest.
Luckily, the invasive plants here in the east are easier to kill than tamarisk. Reed canarygrass and many of our other invasive riparian species share a low tolerance for shade. We go about restoring streamside forests by keeping the herbaceous mat controlled with mowing and spot-spraying of herbicide while our seedlings grow. Within a decade, if the establishment maintenance is completed well and a bit of luck is on the landowner’s side, the shade from densely planted trees and shrubs will be the slow demise of the grass monoculture.
In that time frame, we can also turn a riparian area that is more or less empty of native flora and fauna into a vigorous, biodiverse community of species that were historically present along the stream. In the Chesapeake Bay Watershed, where so much emphasis is on water quality, the habitat gains from restoration practices like riparian forest establishment carry more value than we tend to acknowledge. And conversely, wildlife enthusiast landowners who embark on conservation actions for the critters will be strong contributors to their local water quality improvements.
This is why hearing Willow Flycatchers in Pennsylvania means so much to me. Those Fitz-bews are evidence that our hard work to restore terrestrial habitat and water quality are working. They mean that native vegetation, which actually harbors native fauna, is making a comeback. Which means that our streams can soon too.
We need to listen. Not just to birdsong, but what that means for the land. Some species are bellwethers for ecosystem health. And when we start losing ecosystem health, we can quickly lose ecosystem services, including clean water and air. Does it seem quiet out there to you too? Whether you’re in the Mojave or the mid-Atlantic, riparian zones shouldn’t be.
Are you interested in learning more about riparian forest buffers? You’re in luck! Visit chesapeakeforestbuffers.net for a repository of riparian resources. If you’re a landowner with a stream that needs trees, we can help! Check out our Riparian Forest Buffer Program page to find the staff who serve your area. Streams need forests, and so do we!