Researchers performing a point count.

We investigated the effects on bird community composition and abundance of 1) the width of the forested corridor containing the greenway, 2) the land-use adjacent to the forested corridor, and 3) the habitat structure within the greenway.

Bird species using greenways for breeding were identified using a point count technique during the breeding season (May-June 2002). Using this method, a researcher stands at a point for eight minutes and records all birds singing within 50 meters of the point on a datasheet. We used the data to estimate the number of different bird species at each point and their abundance.

We are particularly interested in the presence of "forest interior" bird species -- birds that are present only in relatively large forested areas. We'd like to know what combinations of greenway forested corrdidor width and intensity of surrounding development support these species.

Objectives

Stopover habitat consists of areas used by birds for food and shelter during migration. We will determine what factors (e.g. vegetation structure, adjacent land use, greenway width) contribute to the quality of greenways as migratory stopover habitat. We will use this information to develop specific guidelines and recommendations for the design and management of greenways as high quality stopover habitat for birds.

Methods

To assess migrant bird use of the greenways, we will count birds within forty 300-m-long segments of the greenways. We will walk the greenway path within each segment, beginning 50m from each end, and count birds seen and heard within 35m on the wider side of the path. The beginning and end of these segments will be marked with yellow or green dots spray-painted at the edge of the greenway path (as in previous studies). We will conduct counts during mornings, afternoons, and evenings in April and early May. In each greenway segment, vegetation will be measured within four 10 meter radius plots spaced 25 meters apart. Trail width and managed area width will be measured with a meter tape. Adjacent land use and greenway width will be determined from aerial photographs in a Geographic Information System.

What the Public Will See

In March, we will mark the greenway segments. People may see us spray painting the dots on the trail and using GPS units. In April and May, we will count birds during all daylight hours for seven days each week. During May, we will be recording vegetation characteristics. People will see us using equipment such as binoculars, tape recorders, meter tapes, rangefinders, spherical densiometers, and hypsometers, sometimes in the forested area adjacent to the greenway path. Sampling may be repeated in the fall (September / October).

Percent coverage of managed area within the greenway, such as trail and other mowed or maintained surfaces, was a predictor for all but total bird abundance. Abundance and richness of development-sensitive species (neotropical migrant, insectivore, and forest-interior birds) were lowest in greenways containing more managed area.

Total bird abundance decreased with increasing pavement and bare earth in the adjacent landscape and increasing hardwood composition within the greenway. Similary, richness and abundance of development-sensitive species decreased as percent cover of pavement and bare earth adjacent to greenways increased. Neotropical migrant species richness and abundance decreased with increasing amounts of building in the adjacent landscape.

Forest-interior species richness was highest in wide greenways. Narrow greenways less than 50m wide harbored primarily edge-dwelling birds, whereas forest-interior species were present only in greenways wider than 50m. Urban adaptors, such as Mourning Dove, House Wren, House Finch, and European Starling, were most common in greenways less than 100m wide. Acadian Flycatcher, Hairy Woodpecker, and Wood Thrush were recorded primarily in greenways wider than 100m. Black-and-white Warbler, Louisiana Waterthrush, Ovenbird, Prothonotary Warbler, Scarlet Tanager, and Yellow-throated Warbler were recorded only in greenways wider than 300m.

Be creative in finding ways to minimize managed area within a greenway. Mow less, make paved trails narrower, leave certain trails within the system unpaved, and locate trails at the greenway edge to maximize forest interior. If vegetation removal is necessary for sight lines on steep terrain, leave forest litter rather than planting grass or ornamentals.

Conserve wider greenways. Greenways wider than 50m provide habitat for many species, but greenways as wide as 300-600m may be needed to conserve certain development-sensitive species, especially forest-interior specialists and ground-nesting songbirds. When greenways of this width are not realistic, larger non-linear reserves are needed to provide habitat for these species. These might be located as 'nodes' along greenways.

Give priority to the conservation of greenways in areas of lower development intensity. Greenways surrounded by residential areas with high canopy cover, low building density and pavement, and little or no bare earth likely contain the greatest diversity and abundance of development-sensitive birds.

Encourage landowners of property adjacent to greenways to maintain forest canopy. Through education and outreach, neighborhood associations and landowners can be motivated to participate in the conservation of development-sensitive bird species by maintaining vegetation structure on the privately-owned lands surrounding greenways.

Maintain vegetative structure within the greenway by leaving ground cover and understory shrubs. Removal of the understory or shrub layer could decrease bird diversity and abundance.

Poster presented at the Annual Meeting of the International Association for Landscape Ecology, April 2003
Click poster for larger image.