In North America many birds die because they collide withwindows of high-rise buildings. One possible solution to resolvethe problem is to construct windows angled down slightly toward theground, so that they reflect the ground rather than an image of thesky to flying bird. An experiment compared the number of birds thatdied as a result of vertical windows, windows angled 20° ofvertical and windows angled 40° off vertical. The angles wererandomly assigned with equal probability to six windows and changeddaily. Window shape, color and other external characteristics werekept identical. Window locations matched the same locationcharacteristics in terms of ground and sky.

• What other conditions need to be kept identical in thisexperiment to avoid influencing the results?
• Over the course of the experiment 30 birds were killed bywindows in the vertical orientation, 15 were killed by windows setat 20° off vertical and 8 birds were killed by windows set at 40°of vertical. Do birds appear to hit high-rise building windows atrandom and die?
• Now answer the following question: Do the data support theassumption that window angles relative to the vertical do notchange bird death rates from as a result of collision with a windowof a high-rise building?