|  |
Bird Collisions with Windows1
Ruthe Smith and Joe Schaefer2
Background
Bird collisions with windows cause serious injury and death. Estimates of annual avian window strike mortality in the United States range from 3.5 to 975.6 million. This upper figure is said to represent about 5 percent of the 20 billion birds found in the United States.The Problem
There are two explanations why birds hit windows. Many such collisions occur when migrating birds encounter tall buildings with extensive, undetectable glass barriers. Because birds usually are traveling at relatively fast speeds, injuries often are fatal. Increased urbanization and a decline in suitable habitat have resulted in birds traveling closer to human dwellings, and a greater danger of colliding with windows. Also, many people actively attract birds into their yards.During spring and early summer, various birds can be found repeatedly crashing into windows. Although this experience may remind us of an Alfred Hitchcock movie, the birds mean us no harm. They merely are responding to their own reflection in the window. To birds, this image represents an intruder. When the resident bird (usually the male) flies over to defend its territory, the outsider also appears to take up the charge. The result is a collision of both the image bird and the resident bird at the window pane. A bird that has a mate or nest nearby may not take defeat easily.
Attacks can be repeated several times until the bird is knocked unconscious or realizes something other than another bird is involved.
One study found that over 50 percent of bird collisions with house windows resulted in death. All species seemed equally susceptible to mortality after a strike.
If the number of deaths from collisions is so high, why don't we see piles of dead birds surrounding our workplaces and homes? Some birds do not lose consciousness right away and may fly into a tree only to die sometime later. Others may be found by predators such as feral cats, picked up by building maintenance workers, or may simply fall into dense bushes that often are planted close to buildings.
Figure 1. Angling windows panes downward helps prevent birds colliding with their own mirrored images. Solutions
Fortunately, there are a few things we can do to reduce or eliminate bird collisions.Reducing the mirror-effect existing buildings. The best results have been obtained by placing lightcolored material behind the glass to reduce the reflection. White drapes or blinds covering the entire window or, white cloth strips (1in [2.5cm] wide) spaced 4in (10cm) or less apart are recommended to prevent window strikes.
Reducing the mirror-effect in new or remodeled buildings. Window panes, in new or remodeled buildings, should be angled downward so that when level with the window the bird sees a reflection of the ground rather than the sky, trees, or itself (see Figure 1).
Several proposed methods such as hawk silhouettes (see Figure 2), wind chimes, and blinking lights have not been proven to significantly reduce bird strikes.
Caring for Injured Birds
Some birds may not be injured severely and will recover with the proper care. If you find a bird that has hit a window, put it in a paper bag or small cardboard box that can be covered securely. Keep the bird in a warm (room temperature) area that is quiet and free from disturbance. Avoid handling the bird and the box as much as possible because this can cause the creature stress, which may hinder recovery. Visually check the bird about every half-hour to see if it has regained strength. Be careful, the bird may be able to fly out of the box. Once it seems to have recovered, take the box outdoors and set the bird free.If the bird does not recover within a few hours, more detailed help may be needed. The telephone number and address of a licensed rehabilitator who has the knowledge and experience to deal with these situations can be obtained from county extension and regional Florida Game and Fresh Water Fish Commission offices. Long-term possession of most birds requires a permit from the U.S. Fish and Wildlife Service.
Footnotes
1. This document is WEC-27, one of a series of the Wildlife Ecology and Conservation Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date June, 1991. Revised September, 2002. Reviewed September, 2002. Visit the EDIS Web Site at http://edis.ifas.ufl.edu.2. Ruthe Smith, former wildlife assistant, and Joe Schaefer, Ph. D., urban wildlife specialist, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, 32611.
The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other extension publications, contact your county Cooperative Extension service.
U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Larry Arrington, Dean.
Copyright Information
This document is copyrighted by the University of Florida, Institute of Food and Agricultural Sciences (UF/IFAS) for the people of the State of Florida. UF/IFAS retains all rights under all conventions, but permits free reproduction by all agents and offices of the Cooperative Extension Service and the people of the State of Florida. Permission is granted to others to use these materials in part or in full for educational purposes, provided that full credit is given to the UF/IFAS, citing the publication, its source, and date of publication.