New experiments by Daniel Klem Jr. and Peter G. Saenger of the Acopian Center for Ornithology at Muhlenberg College provide compelling evidence that parachute cords hung vertically in front of clear and reflective windows are effective preventers of bird-window collisions.
In a mowed pasture bordered by trees and shrubs, Klem and Saenger set platform feeders 30 feet in front of wood-framed picture windows filled with different types of glass and then counted the birds that struck the panes. Observers also recorded the flights of individual birds moving from the feeders toward the windows and assessed whether they changed direction and passed around or over a window.
In one trial, collisions with windows covered with the parachute cord accounted for only 4-6 percent of all collisions, a much smaller share than uncovered clear glass, which accounted for 62 percent of total collisions. What’s more, 11 of 12 birds observed flying toward parachute cords spaced 10.8 cm apart (4.25 in) moved to avoid the window, while 10 of 10 birds that flew toward cords spaced 8.9 cm apart (3.5 in) avoided the window.
“The frequency of bird strikes at clear and reflective panes covered by the two spacing versions of vertically hung parachute cord provide additional evidence, further validating previous studies that vertical stripes separated by 10 cm or less are effective bird-window collision preventive methods,” write the researchers.
“The effectiveness of vertically hung parachute cords to deter bird collisions is attributable to the critical spacing between cords, and also as important is the placement of the cords over the surface facing the outside.”
Klem and Saenger published their results in the June 2013 issue of The Wilson Journal of Ornithology, the quarterly journal of the Wilson Ornithological Society.
Read the abstract
Klem Jr., D. and P. G. Saenger, 2013, Evaluating the Effectiveness of Select Visual Signals to Prevent Bird-window Collisions. The Wilson Journal of Ornithology 125 (2): 406-411. doi: 10.1676/12-106.1. Abstract.
A version of this article appeared in the October 2013 issue of BirdWatching magazine.