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Landscape and Urban Planning 80 (2007) 153–164

Designing suburban greenways to provide habitat forforest-breeding birds

Jamie Mason 1, Christopher Moorman ∗, George Hess, Kristen Sinclair 2

Department of Forestry and Environmental Resources, North Carolina State University, Raleigh, NC 27695, USA

Received 6 March 2006; received in revised form 25 May 2006; accepted 10 July 2006Available online 22 August 2006

bstract

Appropriately designed, greenways may provide habitat for neotropical migrants, insectivores, and forest-interior specialist birds that decreasen diversity and abundance as a result of suburban development. We investigated the effects of width of the forested corridor containing a greenway,djacent land use and cover, and the composition and vegetation structure within the greenway on breeding bird abundance and communityomposition in suburban greenways in Raleigh and Cary, North Carolina, USA. Using 50 m fixed-radius point counts, we surveyed breeding birdommunities for 2 years at 34 study sites, located at the center of 300-m-long greenway segments.

Percent coverage of managed area within the greenway, such as trail and other mowed or maintained surfaces, was a predictor for all development-ensitive bird groupings. Abundance and richness of development-sensitive species were lowest in greenway segments containing more managedrea. Richness and abundance of development-sensitive species also decreased as percent cover of pavement and bare earth adjacent to greenwaysncreased. Urban adaptors and edge-dwelling birds, such as Mourning Dove, House Wren, House Finch, and European Starling, were most commonn greenways less than 100 m wide. Conversely, forest-interior species were not recorded in greenways narrower than 50 m. Some forest-interiorpecies, such as Acadian Flycatcher, Hairy Woodpecker, and Wood Thrush, were recorded primarily in greenways wider than 100 m. Others, includ-ng ground nesters such as Black-and-white Warbler, Louisiana Waterthrush, and Ovenbird, were recorded only in greenways wider than 300 m.

Landscape and urban planners can facilitate conservation of development-sensitive birds in greenways by minimizing the width of the trail andssociated mowed and landscaped surfaces adjacent to the trail, locating trails near the edge of greenway forest corridors, and giving priority to therotection of greenway corridors at least 100 m wide with low levels of impervious surface (pavement, buildings) and bare earth in the adjacentandscape.

2006 Elsevier B.V. All rights reserved.

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eywords: Breeding birds; Corridor width; Forested greenways; North Carolin

. Introduction

There is increasing recognition that landscapes dominated byuman populations cannot be ignored in the quest to conserveiodiversity (Dale et al., 2000; Miller and Hobbs, 2002). Most

f the increase in human population for the coming decades isxpected to occur in and around urban areas (United Nations,004). Some 150 major cities around the world are located near

∗ Corresponding author at: Department of Forestry and Environmentalesources, Campus Box 8003, North Carolina State University, Raleigh, NC7695-8003, USA. Tel.: +1 919 515 5578; fax: +1 919 515 6883.

E-mail address: chris moorman@ncsu.edu (C. Moorman).1 Present address: 1262 Avon Street N., St Paul, MN 55117, USA.2 Present address: The North Carolina Natural Heritage Program, NCDENR,

601 Mail Service Center, Raleigh, NC 27699-1601, USA.

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169-2046/$ – see front matter © 2006 Elsevier B.V. All rights reserved.oi:10.1016/j.landurbplan.2006.07.002

an planning

iodiversity hotspots (Myers, 1990; Cincotta and Engelman,000), and in the United States urbanization is a primary causeor species decline (Czech et al., 2000). As human populationspread, people convert forests, grasslands, and wetlands intoeveloped landscapes of residential, commercial, institutional,r industrial buildings and associated infrastructure. This landse change alters wildlife habitat and can lead to endangermentnd local extinction of numerous species (Dale et al., 2000;iller and Hobbs, 2002).Native bird species richness typically declines as the den-

ity of human development increases (Nilon et al., 1994;riesen et al., 1995; Savard et al., 2000). These effects are

een in areas developed at even relatively low “exurban”ensities (<0.25 houses/ha) and become increasingly appar-nt at suburban (2.5–10 houses/ha) and urban (>10 houses/ha)evels (Lancaster and Rees, 1979; Beissinger and Osborne,

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54 J. Mason et al. / Landscape and

982; DeGraff, 1987; Blair, 1996, 2004; Melles et al., 2003;raterrigo and Wiens, 2005). As development density and habi-

at fragmentation increase, bird community structure shiftsrom development-sensitive specialists to development-adaptiveeneralists (Nilon et al., 1994). Bird communities in urbannvironments are characterized by high abundances of exoticpecies, resident granivores and omnivores, and few insectivo-ous, migrant species. Conservation efforts that focus on pro-ecting habitat and resources for development-sensitive species,uch as neotropical migrants, insectivores, and forest-interiorpecialists, are most likely to succeed in conserving native birdiversity in developed landscapes.

Greenways have become a popular means of mitigatingome of the negative effects of development, with hundredsf projects completed or underway in North America (Searns,995; Jongman and Pungetti, 2004; Bryant, 2006). “Greenway”s a generic term used to refer to linear protected lands com-osed of natural vegetation, or at least vegetation that is moreatural than in surrounding areas (Smith and Helmund, 1993).reenways provide a range of benefits, including recreation and

ransportation, urban beautification, increased property value,evelopment buffers, floodplain protection, preservation of his-orical, cultural, and environmental resources, and wildlife habi-at (Ahern, 1995; Fabos, 1995; Searns, 1995; Jongman andungetti, 2004). Although often stated as a benefit of greenways

n urban and suburban settings, the contribution of greenwayso wildlife conservation is unclear (Schiller and Horn, 1997;inclair et al., 2005). If urban and landscape planners are touccessfully incorporate the needs of wildlife into greenwaylanning, design, and management, they must know which char-cteristics and environmental factors contribute to a greenway’sildlife habitat value. Ecologists and conservation biologists can

lay an important role in this endeavor by conducting researchn wildlife–greenway relationships and disseminating their find-ngs among land use planners (Miller and Hobbs, 2000; Broberg,003; Jongman and Pungetti, 2004).

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Fig. 1. Distribution of greenway segments in Rale

n Planning 80 (2007) 153–164

Research to date suggests that greenway width, habitat qual-ty within the greenway, and adjacent land use and cover areikely the dominant factors affecting a greenway’s value asildlife habitat (Schiller and Horn, 1997; Rottenborn, 1999;anifold, 2001; Rodewald and Bakermans, 2006). In the United

tates, these factors are regulated, to varying degrees, by munic-pal and county governments through planning and zoning pro-esses. Research findings on the effect of these factors on theuality of wildlife habitat can be applied by governments andther organizations during the planning, design, and manage-ent of greenways, and when designating adjacent zoning dis-

ricts.Our objectives were (1) to determine how forested corridor

idth, adjacent land use and cover, and greenway vegetationtructure and composition affect avian community composi-ion in greenways, and (2) to develop recommendations forhe design and management of urban greenways as habitat forevelopment-sensitive birds such as neotropical migrants, insec-ivores, and forest-interior specialists.

. Methods

.1. Study area

We studied greenways in the cities of Raleigh and Cary,orth Carolina, USA (Fig. 1). Raleigh and Cary are part of

he Triangle Region of North Carolina, within the larger phys-ographic region of the Central Appalachian Piedmont. Thisegion consists mostly of urban–suburban land use within aorest–agriculture mosaic. In recent decades, population growthithin the region has resulted in urban and suburban growth,

eplacing forests and fields with residential, commercial, institu-

ional, and industrial development and infrastructure. The urbanopulation in the region increased by 200%, and the area ofrbanized land increased by 900% during 1950–1990 (Northarolina Chapter of the American Planning Association, 2002).

igh and Cary, North Carolina, USA (2002).

J. Mason et al. / Landscape and Urban Planning 80 (2007) 153–164 155

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ig. 2. Forested corridor width and landscape context were measured for eacherpendicular to the greenway orientation and context was measured in two 300

.2. Study site selection: forested corridor width anddjacent land use

We sampled birds in 34 forested “segments” of publicly-wned greenway, each 300 m long and separated by at least5 m. All greenway segments were mature-forest, riparian corri-ors bisected by a stream or river (minimum stream width = 1 m;aximum = 40 m; mean = 6.59 m). The 34 greenway segmentsere selected to ensure a distribution of samples across a broad

ange of forested corridor width (minimum = 32.5 m; maxi-um = 1300 m; mean = 207.57 m) and adjacent land use com-

inations. We selected segments with relatively homogenousidth and similar land use on both sides. Categories of adjacent

and use we sampled were low-density residential (≤7.5 lots/ha),igh-density residential (>7.5 lots/ha), and office/institutional,orresponding to zoning categories in Raleigh and Cary. Areenway’s width was considered to be the width of the forestedorridor including the stream and both sides of the waterway,hich sometimes extended beyond the legal or protected boundsf the greenway. Greenway forested-corridor width and adja-

ent land use were determined using digital aerial photogra-hy and land-use and zoning maps. Digital data were obtainedrom Wake County, the City of Raleigh, and the Town of CaryFig. 2).

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greenway segment using aerial photography in ArcGIS. Width was measured300 m areas on either side of the forested corridor.

.3. Adjacent land cover

Because land cover varies within land use zones, we furtheruantified the land cover adjacent to each segment by analyz-ng 1999 leaf-off digital aerial photography. Two 300 m × 300 mquares were drawn on either side of the study segments, adja-ent and parallel to the forested corridor (Fig. 2). Each squareas populated with a systematic grid containing 100 points. At

ach point, we recorded the land cover in the following cat-gories: canopy, pavement, building, lawn, water, agriculture,nd bare earth. Because photography was leaf-off, we recordedoints that fell within a deciduous tree crown as canopy. At pointshere pavement, building, lawn, water, or agriculture could be

een beneath a tree crown or canopy, both land cover categoriesere recorded for that point. We used these observations to cal-

ulate the proportion of each land cover category adjacent toach study site.

.4. Bird surveys

Using 50 m fixed-radius point counts of 8 min duration, weurveyed breeding birds from 15 May to 30 June 2002 and 2003Ralph et al., 1993; Hamel et al., 1996). Point counts were sit-ated at the midpoint of the 300 m segments, so the centers of

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56 J. Mason et al. / Landscape and

ll count circles were separated by at least 375 m. Each pointount center was located at the approximate center of the green-ay segment’s forested corridor because our goal was to detect

ny forest-interior specialist species in the greenway. Counts inider greenways did not sample edge habitat and likely pro-ided poor measures of edge-dwelling birds there. Conversely,he 50 m radius count circles placed at the center of narrow green-ays (<100 m) extended beyond the forest boundary often into

esidential or commercial grounds characterized by ornamen-al landscapes and managed lawn. Therefore, point counts inarrow greenways recorded the entire bird community withinhe greenway, including edge-dwelling species and any forest-nterior species present. At all segments, the point count includedr was adjacent to a stream, and would therefore be considerediparian habitat. Segment centers were identified on aerial pho-ography and were located and flagged in the field using a globalositioning device. We recorded point count station coordinatesn the field using a global positioning device and verified theocations on aerial photography.

Two observers surveyed each segment a total of four times in002 and one observer surveyed each segment twice in 2003. In002, the two observers were rotated, so that each site was visitedwice by each of the observers. All 34 greenway segments wereisited before a new round of surveys began. All point countsere conducted in the mornings between 6:00 and 11:00 a.m.,

nd under fair weather conditions. The order in which segmentsere visited was rotated to avoid bias because of time of day.ach site was visited during the early, mid-, and late morningt some point during the study. Birds detected outside the 50 mount circle or flying over the plot were not included in analyses.point count was discarded if disrupted by rain, strong gusts ofind, construction or maintenance equipment, or any other sig-ificant disturbance that made it difficult to hear birds. Becauseature forest was the surveyed habitat type at all segments, we

id not expect differences in detectability across sites.

.5. Guilds

Each bird species encountered during our research wasssigned to foraging (breeding season), nesting, migratory, andabitat guilds (Appendix A; Hamel et al., 1982; Ehrlich et al.,988; Moorman and Guynn, 2001). We defined short-distanceigrants as those species with winter ranges that do not include

he Triangle Region of North Carolina, but do include some por-ion on the southeastern region of the United States. We refer toevelopment-sensitive species as those that fall in the neotropi-al migrant, insectivore, or forest-interior guilds (DeGraff, 1987;lair, 1996; Villard, 1998).

.6. Greenway composition and vegetation structure

We visited each greenway segment during September 2002 toharacterize the greenway composition and vegetation structure

ithin the 50 m radius point count plot. We recorded greenway

omposition as the percentages of each 50 m radius plot cov-red by mature forest, young forest, managed area, and stream.e defined mature forest as any area covered by trees taller

ccoa

n Planning 80 (2007) 153–164

han 6 m. Young forest included woody vegetation 1–6 m tall.anaged area included mowed and maintained surfaces, roads,

arks, trails, and ball fields. Percent covers for each class (matureorest, young forest, managed area, and stream) summed to00% for each plot. Greenways with forested corridor widthsarrower than 100 m often had higher amounts of managed areaecause the 50 m plots extended beyond the greenway bound-ry onto the adjacent landscape. However, greenway width andanaged area were not highly correlated (Pearson correlation

oefficient = −0.45), so these variables were treated indepen-ently and in fact behaved differently in analyses.

All 50 m radius plots contained areas of mature forest cover,nd most plots were dominated by this cover type. Within theature forest cover class, percent canopy cover, canopy height,

ercents pine and hardwood, percent vine cover, percent shrubover, and percent ground cover were recorded. We visually esti-ated percents vine cover, shrub cover, and ground cover for thehole plot and recorded as 0 = absent, 1 = 1–20%, 2 = 21–40%,= 41–60%, 4 = 61–80%, or 5 = 81–100%. We measured percentanopy cover by standing at a single location within the matureorest and averaging four spherical densiometer readings, onen each cardinal direction. Percents pine and hardwood withinhe mature forest cover were visually estimated to the nearesthole number for the entire plot. We measured canopy heighty reading the height of the tallest canopy tree within the plotsing a sonar hypsometer.

At each plot, we recorded distance from the plot center to thetream edge and stream width. We recorded distance from thelot center to the trail’s edge, trail surface type (paved, gravel, orirt), trail width, and managed width. Managed width includedhe trail and any mowed or maintained area adjacent to the trail.

e counted the number of snags within the 50 m radius plot,efining snags as standing dead wood taller than 2 m and greaterhan 10 cm in diameter.

.7. Data analysis

We calculated total species richness for each greenway seg-ent as the total number of bird species recorded during each

ear, and guild species richness values were calculated as theumber of species of a particular guild recorded during eachear. Individual species abundances were calculated as the aver-ge number of adult males of a species recorded during all visitsithin a year. We calculated total bird abundance and guild

bundances as the sum of individual abundances. Because rela-ionships between dependent and independent variables wereimilar between years, we performed all analyses on the aver-ge abundance and richness values for the 2 years.

We tested for correlation among all independent variables,ncluding forested corridor width, landscape context, and green-ay composition and vegetation structure measures. Strong cor-

elation among independent variables would violate the assump-ion of non-collinearity necessary for regression analysis. We

onsidered a pair of variables highly correlated if the Pearsonorrelation coefficient (r) was greater than 0.6. We removedne member of each pair of highly correlated variables, makingn effort to remove the variable which we considered less use-

J. Mason et al. / Landscape and Urba

Table 1Greenway forested corridor width, landscape context, and greenway composi-tion and structure measures used in multiple regression analyses on total speciesrichness and abundance, and guild species richness and abundance measuresfrom Raleigh and Cary, NC greenways (2002–2003)

Variable Description

Corridor width Average width (m) of the greenway forested corridor

Landscape context (in two 300 m × 300 m areas adjacent to either side ofthe segment)Canopy Proportion of canopyBuilding Proportion of buildingPaved Proportion of pavementLawn Proportion of lawn coverEarth Proportion of bare earthWater Proportion of water

Greenway composition and structureTrailDist Distance (m) from the point count center to trail edgeYoungFor Percent of count area covered in young forest (1–6 m)Managed Percent of count area covered by human management

(lawn, trail, etc.)StrWidth Width (m) of greenway stream or riverHardwd Percent of the mature forest in count area composed of

hardwoodsCanHt Height (m) of tallest tree in count area as measured by

sonar hypsometerVine Index of percent vine cover in count area in 20%

intervals (1–5)Shrub Index of percent shrub cover in count area in 20%

intervals (1–5)Ground Index of percent ground cover in count area in 20%

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ul in greenway planning and management. Distance to streamr = 0.22) and distance to trail (r = 0.25) were not correlated withorested corridor width; therefore, these variables likely did notontribute to differences in bird communities between narrownd wide greenways. The reduced set of independent variablessed in analysis was average corridor width, six landscape con-ext variables, and nine greenway composition and structureariables (Table 1). We performed backwards stepwise multi-le regression on total bird abundance and species richness anduild abundance and species richness values. All dependent vari-bles were square-root transformed for regression analysis.

Because guilds represent a crude attempt to group bird speciesith similar life history traits, analyses using guilds can be

onfounded by individual species’ responses. For example, auild analysis may appear non-significant, because one speciesithin the guild may have responded positively to a treatmenthile another species responded negatively. The two species

n this case cancel each other out when lumped into a guildlass. Therefore, we used Chi-square tests of independence toetermine if the presence of an individual species was inde-endent of greenway forested corridor width and adjacent landse classes. Segments were classified in the following land use

lasses: low-density residential (≤7.5 lots/ha), high-density res-dential (>7.5 lots/ha), and office/institutional. Previous studiesave indicated thresholds in bird response to varying corridoridths at approximately 50 m (Manifold, 2001; Dickson et al.,

Llwn

n Planning 80 (2007) 153–164 157

995), 100 m (Hodges and Krementz, 1996; Keller et al., 1993),nd wider (Kilgo et al., 1998). Therefore, we assigned segmentso the following forested corridor width classes to reflect thesenown breakpoints and ensure even distribution of greenwayegments among classes: ≤50, 51–100, 101–150, 151–300 and300 m (Table 2). The significance level for all statistical anal-ses was set at α = 0.05.

. Results

We recorded 53 species during our point counts of breedingirds (Table 2). Of these species, 38 were insectivores, 11 weremnivores, 2 were carnivores, 1 was a granivore, and 1 was aectivore. There were 18 cavity nesters, 16 canopy nesters, 13hrub nesters, 5 ground nesters, and 1 brood parasite. Thirty-onef the species were year-round residents of the North Carolinaiedmont, 16 were neotropical migrants, 4 were short-distanceigrants, and 2 were exotic species. Nineteen of these speciesere classified in the interior-edge habitat guild, 17 as edge

pecialists, 11 as forest-interior specialists, 3 as water dwellers,nd 3 as urban specialists.

Forested corridor width was retained only in the final modelor forest-interior richness. The number of these width-sensitivepecies was highest in wider greenways (Table 3).

The amount of managed area within the greenway was theost consistently retained variable in regression models. Total

vian richness, neotropical migrant richness and abundance,nsectivore richness and abundance, and forest-interior speciesichness and abundance all decreased with increasing amountsf managed area within the greenway (Table 3). Percent hard-ood overstory was the other consistently retained compositionariable (Table 3). Total avian richness and abundance and insec-ivore richness and abundance decreased as percent hardwoodncreased. Neotropical migrant abundance and forest-interiorichness increased as stream width increased. Three variablesepresenting adjacent land cover were retained in various finalodels (Table 3). Total bird abundance, neotropical migrant

ichness, and insectivore richness and abundance declined asercent of the adjacent landscape covered by pavement andare earth increased. Forest-interior richness also declined withncreasing bare earth in the adjacent landscape. Neotropical

igrant species richness and abundance decreased with increas-ng building coverage in the adjacent landscape. The relation-hips between birds and vegetation structure were inconsistentTable 3).

Although greenway forested corridor width was a predictoror only forest-interior guild richness, the presence of severalndividual bird species was dependent on greenway forested cor-idor width (Table 2). No forest-interior species were recordedn greenways ≤50 m wide, and Acadian Flycatcher (see scien-ific names in Table 2), Hairy Woodpecker, and Wood Thrushere most commonly detected in greenways wider than 100 m.ther forest-interior birds, including Black-and-white Warbler,

ouisiana Waterthrush, Ovenbird, Prothonotary Warbler, Scar-

et Tanager, and Yellow-throated Warbler, were recorded only inider (>300 m) greenways (Table 2). However, these species didot occur at a sufficient number of sites to statistically determine

158 J. Mason et al. / Landscape and Urban Planning 80 (2007) 153–164

Table 2Breeding bird species occurrences in greenway shown by adjacent land use and width classes (n), Raleigh and Cary, NC (2002–2003)

J. Mason et al. / Landscape and Urban Planning 80 (2007) 153–164 159

Table 2 (Continued )

Adjacent land use abbreviations are: LDR = low-density residential (≤7.5 lots/ha), HDR = high-density residential (>7.5 lots/ha), OFC = office/institutional. Eachcell contains the number of segments in the corresponding greenway class in which the species was recorded during the 2002 and 2003 breeding seasons. aSpeciesp indep

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f species presence was independent of greenway forested corri-or width. Ground-nesting songbirds were rare in our segments.venbird, Black-and-white Warbler, and Louisiana Waterthrushere the only ground-nesting songbirds recorded during point

ounts, and these species were found only in greenways widerhan 300 m. Several interior-edge species, including Blue-graynatcatcher, Downy Woodpecker, and Red-eyed Vireo, alsoere most common in wider (>50 m) greenways. White-eyedireo was recorded only in greenways wider than 300 m. Indigounting, an edge species, only was detected in greenways wider

han 100 m.European Starling, House Finch, House Wren, and Mourn-

ng Dove, all edge or urban-adapter species, were more commonn narrower greenways, especially in greenways ≤50 m wide.

any common species were recorded over all greenway widthsnd land use classes; Northern Cardinal, American Robin, Car-lina Chickadee, Carolina Wren, and Tufted Titmouse wereecorded in 29 or more of the 34 segments (Table 2).

Red-shouldered Hawk, Northern Flicker, and Red-belliedoodpecker were least common in greenway segments with

djacent office/institutional land use. Conversely, Americanrows were most commonly detected in segments surroundedy suburban office complexes (Table 2).

. Discussion

.1. Greenway composition and vegetation structure

The amount of managed area, such as trail and other mowedr maintained surfaces, within a greenway segment was theost consistent factor in predicting neotropical migrant, insec-

ivore, and forest-interior species richness. The number ofevelopment-sensitive species decreased as the amount of man-ged area increased. Most greenway trails in Raleigh and Caryre collocated with sewer lines. Vegetation was removed duringonstruction, and managed surfaces adjacent to trails and rel-

tively wide canopy openings usually were created. The wideanaged areas essentially divided the once contiguous forested

orridor into two narrower corridors, decreasing the habitatalue for development-sensitive species (Villard, 1998). Other

maes

endent of landscape context (P < 0.05).

esearch has similarly shown that generalist birds are more abun-ant near recreational trails in forest and grassland ecosystems,hile development-sensitive birds are less common (Miller et

l., 1998).Minimizing managed area within a greenway is essential to

roviding habitat for development-sensitive species. Greenwaysontaining little or no managed area may provide habitat for upo twice as many development-sensitive bird species comparedo greenways containing 2–4 m wide paved trails with adjacent

owed areas. The goal of minimizing managed area within areenway, however, may conflict with the goal of providingecreation and transportation opportunities to urban residents.rails 2–4 m wide often are constructed within greenways toccommodate access and shared use of paths by bikers, pedes-rians, strollers, and wheelchairs. Additional mowed areas are

aintained to accommodate benches and equipment, to keepree roots from breaking up paved paths, or for aesthetics andafety. These conflicts might be resolved by placing greenwayrails along one edge of a wide forested corridor, rather thanirectly down the middle of the corridor, minimizing the effectf greenway trail management and edge on “interior” forest.

Several bird groupings declined with increasing hardwoodover in the greenways. Typically, avian species richness andensity are lower in coniferous than in deciduous woodlotsJames and Wamer, 1982; Mortberg, 1998; Marzluff and Ewing,001). All of our segments were located in streamside hardwoodabitats. Segments containing some pine may have attracteddditional resident insectivorous species, such as Brown-headeduthatch and Pine Warbler, not found in exclusively hardwood

ites.

.2. Adjacent land use and cover

If conservation of development-sensitive bird species is aoal, priority should be given to the protection of greenwaysocated in areas adjacent to low-density residential develop-

ent that maintains vegetative cover. Many neotropical migrantnd forest-interior species were absent in greenways with barearth, pavement, or high building cover in the adjacent land-cape. Other studies have similarly shown that total bird diver-

160 J. Mason et al. / Landscape and Urba

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n Planning 80 (2007) 153–164

ity and neotropical migrant diversity and abundance decreasen areas of high development intensity adjacent to remnantoods (Tilghman, 1987; Friesen et al., 1995; Rodewald andakermans, 2006). Human development can have several neg-tive effects on birds in remnant forest areas, including but notimited to: concentration of natural and exotic predators and par-sites; increased competition with exotic and human-associatedird species; removal of resources; and disruption of behaviornd movement by human activities (Marzluff and Ewing, 2001).xotic plants are more likely to colonize riparian forest reservesithin more urban landscapes (Borgmann and Rodewald, 2005),

nd birds that nest in exotic plants may experience increased netailure (Schmidt and Whelan, 1999; Borgmann and Rodewald,004).

Adjacent land use may be particularly important for wide-anging species. In our study, no passerine species was depen-ent on the land cover adjacent to greenways, possibly becausehe territories of the relatively small birds are containedntirely within the greenway forested corridor. Conversely,ed-shouldered Hawk, American Crow, and two woodpecker

pecies demonstrated a response to adjacent land use class.ed-shouldered Hawks were recorded primarily in greenways

urrounded by low-density residential land use (≤7.5 lots/ha),ypically with high levels of canopy cover. As a carnivore, theed-shouldered Hawk may respond to habitat factors within

he landscape at a broader scale than other bird species, andreas with extensive hardwood canopy typically are preferreds breeding habitat by Red-shouldered Hawks (Moorman andhapman, 1996). Red-bellied Woodpeckers were less commonnd Northern Flicker was absent in greenway segments sur-ounded by office/institutional land use, possibly because of theow canopy cover in those areas. Conversely, American Crowas most common in segments with adjacent office/institutional

and use. Crows are generalists that most commonly feed on theround in open habitats like that found on the grounds of subur-an office complexes (Verbeek and Caffrey, 2002).

.3. Forested corridor width

Forest-interior species richness was correlated positively withreenway forested corridor width, and no forest-interior speciesere observed in the narrowest greenways. Several interior-

dge species and Indigo Bunting, an edge species, also wereost common in greenways wider than 50 m. Other studies have

hown that neotropical migrant species richness increases withncreasing riparian forest corridor width (Keller et al., 1993;odges and Krementz, 1996; Kilgo et al., 1998). In Washing-

on state, greenways narrower than 40 m had low densities ofround and foliage foragers, residents, and neotropical migrantsManifold, 2001). Greenways wider than 100 m harbored greaterumbers of interior species and greater bird diversity when com-ared to narrower greenways (Manifold, 2001). Rodewald andakermans (2006) concluded that the landscape matrix sur-

ounding Ohio riparian forests was a more important predictor ofhe bird community than forest width alone, and suggested thatraditional management strategies that focus solely on maximiz-ng forest corridor width are insufficient. They did not, however,

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greenways as wide as 300–600 m may be needed to conserve

J. Mason et al. / Landscape and

urvey forest tracts <60 m because the linear habitats generallyacked forest-dwelling birds, which agrees with our findings thatew development-sensitive species occurred in greenways lesshan 50 m wide.

While greenways as narrow as 50 m provided habitat for aiversity of birds, most were common edge species or urbandapters that rank low in terms of conservation priority (Huntert al., 1993). Development-sensitive species were found onlyn wider greenways. The necessary width of a greenway cor-idor depends on the species that are to be conserved. To pro-ect ground-nesting songbirds and some forest-interior species,reenways more than 300 m wide might be needed. Widerreenways were less likely to contain nest parasites such asrown-headed Cowbirds and aggressive exotic species such asuropean Starlings in their interiors. Because our point countlots were located at the greenway center, point counts in widereenways were conducted farther away from the greenwaydge. While starlings and cowbirds were not common in theenters of wide greenways, it is likely that they could be foundt the greenway edges. Internal edges created by trails and otherpenings within wide greenways may provide habitat for thesedge-dwelling species.

One appealing approach to increase the suitability of nar-ow greenways for development-sensitive species might be tombed them in areas of low-density development. During initialtatistical analyses, however, we failed to document interactionsetween greenway forested corridor width and adjacent landse (i.e., bird communities in narrow greenways surroundedy low-density development were similar to those in narrowreenways surrounded by high-density development). Further,orest-interior birds were absent in narrow greenways regard-ess of adjacent land use and cover, and unequal abundances ofndividual species among greenway segments was explained byreenway width alone in most cases. Yet, greenway forestedorridor width and adjacent land cover each affected abun-ance or richness of some species or guilds, indicating thatdditional investigation of width–context interactions might bearranted.Human recreation and the edges created by recreational trails

ight affect avian nest success within a greenway. The effect ofdge on nest predation rates is related to the type of adjacent habi-ats and may vary by region (Donovan et al., 1997; Keyser, 2002).est predation rates often increase nearer to edges, especially ineveloped and agricultural landscapes (Gates and Gysel, 1978;ndren and Angelstam, 1988; Keyser, 2002). The probability ofrood parasitism by Brown-headed Cowbirds also is higher nearome edges, reducing clutch sizes and nest success (Moormant al., 2002). In Colorado greenways, however, the presence ofecreational hiking trails decreased the vulnerability of artificialird nests to predation, presumably because the scent of domes-ic dogs on the trails deterred mammalian nest predators (Millernd Hobbs, 2000).

The potentially large amount of forest edge in linear, subur-

an greenways suggests that nest predation rates may be highhere. In a complementary study using the same greenways seg-

ents as used in this study, Sinclair et al. (2005) determinedhat nest predators, such as raccoons, opossums, squirrels, and

n Planning 80 (2007) 153–164 161

omestic cats, were common. Corvids, such as American Crowsnd Blue Jays, and Common Grackles have been photographedepredating artificial bird nests at our greenway study sitesNovotny, 2003). Mammalian and avian nest predators wereess abundant in the interior of wide greenways (Sinclair etl., 2005), where development-sensitive bird species were mostommon. Wide greenways should provide interior habitat forevelopment-sensitive species while contributing to low nestredation rates because of low density of nest predators.

We did not measure success of real nests in greenwaysBurhans and Thompson, 2006). If birds present in subur-an greenway segments experience low survival and reproduc-ive success, then greenway habitats could be acting as sinksPulliam, 1988). Further, if birds preferentially choose to breedn linear greenway habitats that are poorer in quality than otherotential breeding sites (e.g., non-linear parks or reserves),reenways could be acting as ecological traps (Battin, 2004).urther investigation is needed to determine if greenways act asinks or ecological traps, providing habitat in which birds estab-ish territories but do not survive or reproduce successfully.

The land adjacent to most of the greenways we studied waswned by private homeowners and businesses. In the casesf many of the widest greenways, only a small portion oforested corridor was comprised of land protected legally asgreenway.” Wider publicly-owned greenways would requirereater forethought, planning, and expenditure of public funds.s greenways wider than 50 m are not a realistic option for manyunicipalities, typical urban and suburban greenways may not

uffice to conserve certain development-sensitive, forest-interiorird species. Larger nature preserves or public parks likely areecessary to conserve these species.

. Management recommendations

Based on our results, the following guidelines may be usefulo urban and landscape planners in the design and managementf greenways as habitat for development-sensitive bird species:

. Be creative in finding ways to minimize managed area withina greenway. Mow less, make paved trails narrower, leavecertain trails within the system unpaved, and locate trails atthe greenway edge to maximize forest interior. If vegetationremoval is necessary for sight lines on steep terrain, leaveforest litter rather than planting grass or ornamentals. Rec-ommendations for specific maximum trail widths are difficultto formulate because of regional variations in bird communi-ties and environmental factors. Instead, we suggest that trailsand the associated managed areas be narrow enough that theforest canopy remains relatively unbroken.

. Conserve wider greenways. Greenways of at least 100 m wideprovide habitat for some development-sensitive species, but

certain forest-interior specialists and ground-nesting song-birds. When greenways of this width are not realistic, largernon-linear reserves are needed to provide habitat for thesespecies. These might be located as “nodes” along greenways.

1 Urba

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62 J. Mason et al. / Landscape and

. Encourage developers of property adjacent to greenways tominimize pavement, building, and bare earth cover. Througheducation and outreach, developers and landowners can bemotivated to participate in the conservation of development-sensitive bird species by limiting impervious surface andretaining native vegetation on the privately-owned lands sur-rounding greenways.

cknowledgments

We thank Marcia Gumpertz and Janet Bartz for advice anduidance on statistical analysis. We thank Nathan Tarr for an

fp

Appendix A. Breeding bird species recorded during our study,

n Planning 80 (2007) 153–164

mmense amount of work locating and marking study sites andonducting bird surveys; the City of Raleigh, Town of Cary,emlock Bluffs Nature Preserve, and William B. Umstead Stateark for graciously allowing us to conduct research on their

ands; and Wake County GIS, City of Raleigh GIS, and Town ofary GIS for provision of geographic data. Finally, we thank

he North Carolina State University Department of Forestrynd Environmental Resources and the USDA Forest Serviceor providing the funds and resources to make this researchossible.

classified into four different guilds

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J. Mason et al. / Landscape and

ppendix A (Continued )

ey

oraging guilds Nesting guilds Migratory guilds Habitat guilds

= Insectivore P = Brood Parasite E = Exotic E = Edge= Nectivore C = Canopy N = Neotropical I = Forest-interior= Omnivore G = Ground R = Resident IE = Interior-edge= Carnivore S = Shrub S = Short-distance U = Urban= Granivore V = Cavity W = Water

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