Restoration of Riparian Habitat: It Helps Birds
Written by Andy McCormick
Andy McCormick, volunteer of Eastside Audubon
While researching some literature in preparation for Eastside Audubon’s upcoming bird survey of the Willowmoor Project area at Marymoor Park, I learned that by taking into consideration some important elements of restoration design and new plantings, restoration of riparian habitat could significantly improve bird abundance and diversity in an area that had previously become degraded.
The Willowmoor Project, formerly named the Willowmoor Floodplain Restoration Project, proposes to reconfigure an area known as the Transition Zone between Lake Sammamish and the main channel of the Sammamish River within Marymoor Park in Redmond, WA. A new winding channel has been designed to be constructed alongside the existing channel to improve habitat for Chinook salmon, steelhead, and other fish and wildlife species. Birds are not explicitly mentioned in the proposal, but the Eastside Audubon Conservation Committee with consultation from the Puget Sound Bird Observatory, has designed a bird survey to measure bird abundance and diversity in the area before and after the construction of the new waterway.
Pacific-slope Flycatcher by Mick Thompson
RIPARIAN HABITAT
Riparian habitat is known to be important for the biodiversity of plants, birds, and other wildlife. The riparian zone forms along the interface of land and a river or stream and is characterized by woodlands comprised of trees of varying height, shrubbery, and some grasslands and wetlands. The Willowmoor Project area is in a riparian zone along the Sammamish River.
In many areas degradation of riparian habitat has resulted from overuse, farm animal encroachment, and urban development. In Washington and other western states, riparian areas are now a major focus for habitat restoration. One of the largest riparian restorations in Washington has been the removal of two dams from the Elwah River. Many smaller restorations have produced improvements in habitat for fish and birds.
BIRDS OF RIPARIAN HABITAT
Review of a few studies of riparian restoration projects will provide some examples to aid our understanding of this productive vegetation zone. One California study categorized birds into three types. Some were riparian-dependent species such as Western Wood-Pewee, Pacific-slope Flycatcher, Common Yellowthroat, Yellow Warbler, Song Sparrow, and Spotted Towhee. These bird species need riparian habitat for breeding.
A second group included woodland species such as Anna’s Hummingbird, Downy Woodpecker, Northern Flicker, Bewick’s Wren, American Robin, and American Goldfinch. This second group will use riparian areas for breeding and foraging but will also breed in other habitats. The third category was synanthropic species (those that have adapted to humans) and included American Crow, European Starling, Brewer’s Blackbird, House Finch, and House Sparrow.
Following restoration of the sites researchers found that the diversity of the riparian-dependent species more than doubled, the diversity of the woodland species quadrupled, and the population of the synanthropic species remained low. The authors concluded that restoration of riparian habitat is good for the birds that need it the most.
FOCAL SPECIES FOR STUDY
Another California study focused on four focal species (Black-headed Grosbeak, Yellow-breasted Chat, Song Sparrow, and Yellow Warbler) and detailed their territories and breeding sites using a pre-test on remnant sites of the original riparian habitat, and a post-test on the restoration site. They found that these four species selected aspects of more complex habitats. Yellow Warblers, for example, preferred greater cover. Song Sparrows are one of the first avian colonizers of early successional riparian vegetation and were considered an indicator species of the early stages of a restoration project.
The birds preferred the remnant sites. The restoration sites were only 3-10 years old during the study, and the results suggest that it might take many years for birds to use restoration sites as much as older riparian areas.
RECOMMENDATIONS FOR RESTORATION PROJECTS
Providing diversity in vegetation selected for planting and increasing the variation in tree species and tree height will provide a more complex habitat, which is preferred by many bird species. Because nest predation was found to be the greatest danger for nesting birds, one study recommended managing plantings to enhance a dense shrub layer. Shrub density will help increase cover and protection for breeding spaces.
Finally, most of the studies I read (nine) recommended continued habitat restoration and long-term monitoring of the growth of the new vegetation. Improving riparian habitat clearly helped increase suitable habitat for birds and increased both abundance and diversity in several of the restored sites. One study also showed that restoration in one area led to increases in bird abundance in other areas.
VOLUNTEERS NEEDED FOR THE MARYMOOR PARK BIRD SURVEY
Eastside Audubon is now recruiting volunteers to participate in this ongoing study. Volunteers will be provided training in bird identification by sight and sound. Any interested person may join the study. Birding expertise is not required. We will train you and you can improve your birding skills while participating in this study. Join us by registering at the EAS website www.eastsideaudubon.org.