Power lines that bisect daily avian movement corridors, such as those between roosting and foraging sites, have historically been most associated with avian collisions ( Bevanger and Brøseth 2004, Stehn and Wassenich 2008, APLIC 2012), with the risk of collision exacerbated in low light, fog, and inclement weather ( Savereno et al.
For example, across 3 studies, 72% of 373 observed collisions were with overhead shield wires ( Faanes 1987, Pandey et al. When encountering transmission lines, birds appear to see large-diameter energized wires (conductors) and avoid them by adjusting flight altitudes upward, subsequently colliding with smaller-diameter, less-visible overhead shield wires that are used for lightning protection ( Jenkins et al. 2009, APLIC 2012), but appear to be relatively uncommon compared with collisions involving other species groups.
Collisions involving raptors have occurred ( Mojica et al. 2016), although this may be partly a function of detection bias limiting incidental observations of smaller species ( Drewitt and Langston 2008, Rogers et al. Large, heavy-bodied species such as swans, pelicans, herons, and cranes are generally thought to be more susceptible to power line collisions than smaller, more maneuverable species ( Jenkins et al. If similar patterns occur at other lines that cross diurnal migration corridors along ridges, then future monitoring may be better focused on potentially riskier settings, such as areas where migrating birds do not have deflected winds to assist with gaining elevation.Īvian collisions with power transmission lines (≥60 kilovolts APLIC 2012) are a global conservation concern ( Quinn et al. Altered flight elevations and the absence of observed collisions supported hypothesis 3. Postconstruction, raptors responded to the new line by flying higher than they had when traversing the previous line. A few passed through (5%) or below (3%) the S-R wire zone. Most raptors (92%) crossed above the S-R wire zone. Postconstruction, we recorded 4,482 crossings. Some (24%) passed through the anticipated S-R wire zone, and a few (4%) passed below the anticipated S-R wire zone. Most raptors (72%) crossed above the anticipated S-R wire zone. Preconstruction, we recorded 3,698 raptor crossings. To evaluate these hypotheses, we recorded the flight elevations of migrating raptors in 2013 before construction of the S-R line and in 2014 postconstruction.
We hypothesized that the S-R line, which on Kittatinny Ridge includes markers designed to increase its visibility to birds, would cause migrating raptors to react in 1 of 3 ways: (1) to not alter flight elevation, but to pass safely through the S-R wire zone (2) to not alter flight elevation, and to not pass safely through the wire zone, leading to collisions or (3) to alter flight elevation and to pass safely above or below the S-R wire zone. The S-R line crosses Kittatinny Ridge, a corridor for raptors migrating south through New Jersey and Pennsylvania, USA. We studied potential collisions where an existing power line supported by towers 20–25 m tall was replaced by the Susquehanna-Roseland line (S-R line), a new line with towers 55–60 m tall. Avian collisions with overhead power lines are of conservation concern, particularly in migration corridors.