BANG! We were in the middle of a tai chi class, enjoying the view outdoors, when a bird slammed into the lower portion of a large window array and dropped to the ground. Then another one hit. The second one flew away. The first, a northern junco, broke its neck.
Thousands of birds were flying through Cape May County, an area known globally for its amazing migratory bird movements. Many songbirds migrate at night, and in the morning, they find themselves in unfamiliar territory.
The birds fly and forage in loose flocks until they get favorable winds to continue their journey. These spring and fall migrations are fraught with peril: storms, predators, cars and, increasingly, window strikes.
People know not to walk through glass doors because we see doorknobs and frames to clue us into the presence of glass. But without these clues or if you are not paying attention and make the mistake of walking into a glass door or wall, not only is it a surprise, but it hurts.
Birds’ visual perceptions differ from humans. Most birds have eyes on the sides of their heads, so they have relatively little depth perception. This helps with an avian lifestyle but not in perceiving glass.
They see a reflection of the outdoors and have no reason to believe that they can’t fly “through” that reflection to get to additional habitat. They may also see transparent glass – windows placed opposite each other in a room or hallway – to be an unobstructed avenue for escaping a predator.
It is estimated that up to one billion birds die or are seriously injured in the United States due to collisions with glass-reflective buildings, façades, and window arrays.
Birds are a rich part of Cape May County’s natural fabric. Besides preserving our county’s diverse habitats and keeping cats indoors, protecting birds from window collisions could be one of the easiest actions that everyone who owns a home or maintains a building can do.
As a general note, if you are feeding birds, try to place your feeders around 30 feet away from windows. This gives birds a chance to navigate around the windows when they are disturbed.
While collisions occur all year round, they are particularly egregious during spring and fall migration. The following preventative measures may not be 100% effective but doing something is better than doing nothing.
Window Cleaning, Screens, and Nets
Bypass cleaning the outside of your windows (Yes, you heard it!). Having sparkly clean windows makes reflections crisp and convincing. Consider leaving your outside screens on all year as they help break up the reflection. And if a bird does fly into the window, the screen acts like a little net that helps cushion the blow. Drape a section of nylon netting about 1 foot out from the window. Weigh the netting down with wood to keep it rigid. You will barely see the netting, but it will be enough for the birds.
Exterior Window Deterrents
Stick decals or dots, draw lines, or paint designs on the outside of the windows. Any of these elements need to be placed close enough to each other so that the birds don’t perceive they can fly through the open space between the elements. Think of it like this. When birds fly through wooded areas, they see tree branches and the spaces in between those branches. It is those “in-between” spaces that they aim for in flight. The recommended spacing for any elements is 2 inches high and 4 inches wide (some suggest 2×2 inch spacing).
Ultraviolet (UV) decals or reflective stickers: UV decals or reflective stickers placed randomly on the outside of the glass is a good first step but putting them close together according to the recommended spacing gives the birds a better frame of reference. Kudos to the Cape May County Library – Sea Isle City Branch which has taken the first step to reduce bird collisions by placing window decals on its education room windows.
Lines and Painting Designs: Drawing vertical lines on the outside of the glass with a white paint marker can be extremely effective. The lines remain until the windows are washed. While this seems counterintuitive to wanting to see outside, the lines, while noticeable, are not objectionable. And it is a great way to educate people about reducing bird mortality. Painting designs on the outside of the windows with white tempura paint can also be effective and a great way to involve children.
Dots or Deterrent Markers: Purchase transparent films or rolls of dots to adhere to the outside of the window. The dots are preset to the recommended spacing and are a mostly permanent solution.
New Construction
Bird researchers have worked with the construction industry to modify glass before it is placed into window frames. Windows may be “fritted” which etches patterns into the glass. Groups are also testing UV light collision avoidance which has been shown to be effective as an avoidance measure for power lines.
Here are some great resources:
- New Jersey Audubon: njaudubon.org/keeping-birds-safe/
- Feather Friendly: featherfriendly.com/
- American Bird Conservancy: abcbirds.org/solutions/preventing-collisions/
Cape May, Naturally is a twice-monthly column written by a rotating cast of experts at the New Jersey Audubon about birding and nature on the Cape.
