Article

Long-term effects of rights-of-way maintenance via the wire-border zone method on bird nesting ecology

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Abstract

The State Game Lands (SGL) 33 Research and Demonstra-tion 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 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 States and because species dependent on these habitats are showing popula-tions 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. 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 (Dumetella carolinensis), eastern towhee (Pipilo erythrophthalmus), common yel-lowthroat (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 mainte-nance on bird nesting ecology.

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Natural ecological disturbance creates habitats that are used by diverse groups of birds. In North America, these habitats or ecosystems include grasslands or prairies, shrublands, savannas, early successional forests, and floodplains. Whereas the extent of all natural habitats has diminished significantly owing to outright loss from agriculture and development, the suppression of disturbance by agents such as fire and flooding has led to further losses. Accordingly, the abundances of many bird species adapted to disturbance-mediated habitats have declined as well. In North America, these declines have been more severe and common than those of species associated with less frequently disturbed habitats such as mature or closed-canopy forests. Field studies consistently reveal the direct role of disturbance and successional processes in structuring avian habitats and communities. Conservation strategies involving the management of disturbance through some combination of flooding, application of fire, or the expression of wildfire, and use of certain types of silviculture have the potential to diversify avian habitats at the local, landscape, and regional scale. Many aspects of the disturbance ecology of birds require further research. Important questions involve associations between the intensity and frequency of disturbance and the viability of bird populations, the scale of disturbance with respect to the spatial structure of populations, and the role of natural vs. anthropogenic disturbance. The effects of disturbance and ensuing successional processes on birds are potentially long-term, and comprehensive monitoring is essential. * The US Government has the right to retain a nonexclusive, royalty-free license in and to any copyright covering this paper.
Article
Observations of 21 species of open-nesting passerines breeding in contiguous field and forest habitats at Rose Lake Wildlife Research Area, Michigan, were made during 1974 and 1975. Data were collected on nest dispersion, clutch-size, and fledging success in relation to the field-forest edge. Losses of eggs or nestlings were attributed to predation, inclement weather, Brown-headed Cowbird (Molothrus ater) parasitism, nest desertion, hatching failure, and adult death. Each bird species seemed to have a preferred distance from the habitat discontinuity that was used as a nest site. Furthermore, nests were not uniformly distributed on the area. Over one-half of the nests were found within ?15 m of the habitat discontinuity. Seventy-five percent of the nests belonged to birds characteristic of mixed breeding habitats, i.e., birds requiring an open overstory canopy with elevated singing and observation perches and dense cover near the ground for nesting and feeding. These mixed-habitat species also accounted for the increase in avian species nesting near edges. Based on Kendall rank and partial rank correlation tests, increasing numbers of nests and the percentage of total clutches ^3 eggs were found to be negatively correlated with increasing distance from the habitat discontinuity. Correlation between fledging success and increasing distance from the edge was positive and highly significant. Of the several mortality factors investigated, predation and cowbird parasitism were found to be the most important. The increased predation rate with decreased distance from the edge was attributed primarily to a functional response to higher numbers of nests and a greater activity of potential nest predators in the vicinity of the habitat discontinuities. Our results indicate that habitat suitability decreases with increasing numbers of nests toward the narrow field-forest edges. Although such abrupt habitat discontinuities did attract a variety and abundance of birds characteristic of habitats with mixed life-form, these discontinuities seemed to function as "ecological traps" by concentrating nests and thereby increasing density-dependent mor? tality. Ironically, the cowbird was also a victim of the increased predation rate. As these man-made forest edges are of recent origin, they are perhaps unrepresentative of the ecological niche in which these species evolved, and thus they may be poorly adapted to cope with the increased nest predation.
Terrestrial vertebrates in Pennsylvania: Status and conservation in a changing landscape
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Effect of vegetation maintenance of an electric transmission line right-of-way on reptile and amphibian populations
  • R H Yahner
  • R J Hutnik
  • S A Liscinsky
Yahner, R.H., R.J. Hutnik, and S.A. Liscinsky. 2001a. Effect of vegetation maintenance of an electric transmission line right-of-way on reptile and amphibian populations. J. Arboric. 27:24-28. ---. 2002a. 50 Years of Continuous Study: 1953-2002: State Game Lands 33 Research Project. Annual Report to Cooperators. 40 pp. ---. 2002b. Bird populations associated with an electric transmission right-of-way. J. Arboric. 28:123-130. ---. 2003. Green Lane Research and Demonstration Project: 17 years of continuous study. Annual Report to Cooperators. 28 pp.