LONG-TERM EFFECTS OF RIGHTS-OF-WAY MAINTENANCE VIA THE WIRE-BORDER ZONE METHOD ON BIRD NESTING ECOLOGY

Journal of Arboriculture, Sep 2004 by Yahner, Richard H, Ross, Bradley D, Yahner, Richard T, Hutnik, Russell J, Liscinsky, Stephen A

Abstract. The long-term nesting ecology of birds was studied during 2002 and 2003 on the State Game Lands (SGL) 33 Research and Demonstration Area, which is located along a 230-kV transmission right-of-way (ROW) of FirstEnergy (Penelec) in the Allegheny Mountain Region, Centre County, Pennsylvania, U.S. The objectives of this study were to compare nest abundance, success, and placement (1) in handcut versus herbicide-treated study sites (units) and (2) in wire versus border zones. In addition, results from this study were compared to those obtained in a previous study conducted in 1991-1992 on the ROW to better understand the long-term effects of vegetation maintenance management on wildlife. Thirty-three and 26 nests of 10 bird species were noted in 2002 and 2003, respectively. The most frequently encountered nests in 1991-1992 and 2002-2003 were those of bird species adapted to early successional habitats, for example, eastern towhee (Pipilo erythrophthalmus), created by the wire-border zone method of vegetation maintenance on the ROW. Thirteen (39%) of 33 nests of all species combined fledged young in 2002 compared to 17 (65%) of 26 nests in 2003. Nesting success in 2003 on the SGL 33 ROW was typical of most studies of bird nesting success in a variety of habitats and was comparable to that recorded in 1991-1992. The low-volume basal unit was more important as nesting habitat than either handcut or mowing plus herbicide units, with nine species nesting in the low-volume basal unit versus only four species in each of the other two units. Thirty-five (59%) of the 59 nests on the ROW were in wire zones, whereas 24 (41%) nests were in border zones. In conclusion, mowing plus herbicide treatment on a ROW may be the best application of the wire-border zone method in terms of resistance to seedling invasion of undesirable trees, cover-type development in the wire zone, and its value as wildlife habitat. Because early successional habitat is becoming less common in the eastern United Slates and because species dependent on these habitats are showing populations declines, the maintenance of a ROW via the wire-border zone method is extremely valuable to the long-term conservation of early successional bird species.

Key Words. Breeding birds; handcultmg; herbicides; nesting ecology; rights-ol-way; vegetation.

The State Game Lands (SGL) 33 Research and Demonstration Project in Centre County, Pennsylvania, U.S., has been studied since 1953, making this 51-year-old project the longest continuous project documenting the effects of mechanical and herbicidal maintenance on flora and fauna along an electric transmission right-of-way (ROW) (Yahner et al. 2002a; Vistas 2003). Transmission ROW are linear corridors that often traverse contiguous forests, thereby making these ROW extremely valuable for bird species requiring early successional habitats (Bramble et al. 1992a, 1994; Yahner et al. 2002a; Yahner 2003a). For instance, most nests found on the SGL 33 ROW in 1991-1992 were those of early successional species, including field sparrow (Spizella pusilla), gray catbird (Dumeteua carolmensis), eastern towhee (Pipilo erythrophthalmus), common yellowthroat (Geothlypis trichas), and indigo bunting (Passerina cyanea) (Bramble et al. 1994).

Early successional habitat has become less common in the forests of the eastern United States in recent decades (Trani et al. 2001), and the maintenance of a ROW via the wire-border zone method creates early successional habitat for bird populations (e.g., Yahner et al. 2002b). Thus, because bird species adapted to early successional habitat have experienced population declines over recent decades in the northeastern United States (Robbins et al. 1989; James et al. 1996; Yahner 2000, 2003a; Askins 2001; Brawn et al. 2001), a ROW, if properly maintained using the wire-border zone method, represents important nesting habitat for many bird species.

In the present study, we examined the long-term response of breeding birds to ROW vegetation maintenance on SGL 33 in the Allegheny Mountain Region of central Pennsylvania in 2002 and 2003. The objectives of this study were to compare nest abundance, success, and placement (1) in handcut versus herbicidal-treated study sites (units) and (2) in wire versus border zones. In addition, results from this study then were compared to those obtained in a previous study conducted on the ROW in 1991-1992 (Bramble et al. 1994) to better understand the long-term effects of ROW maintenance on bird nesting ecology.

METHODS

The wire-border zone method of vegetation maintenance was initiated on the SGL 33 ROW in 1987 (Bramble et al. 1992a) (Figure 1). This method of vegetation maintenance along a ROW is designed to produce a tree-resistant forb-grass-shrub cover type in wire zones while simultaneously maintaining a tall shrub cover type in border zones. As a result, the wire-border zone method creates a diverse wildlife habitat on the ROW, with low-lying vegetation in wire zones and taller vegetation in border zones to produce habitat diversity. The total area of wire zones was approximately equal to that of border zones.