The purpose of developing this estimate was to provide a baseline which permits us to understand the increased avian mortality if the promotion of the lights out program reduces the utilization of the collision prevention systems. Since light reduction advocacy only asks a building owner to Hi turn off their lights, they will in almost every instance choose that option rather than investing in a bird window collision prevention system.
The estimate was developed as follows.
I first obtained the total square footage of the product which the three major suppliers have sold or the total number of the products they have sold. Based on conversations with the suppliers, I determined what percentage of the square footage is commercial versus residential. Based on estimates provided by one of the suppliers, I determined the typical size of a commercial installation. I based the estimate of the square footage of glass needed for a home based on my experience as published in the Consumer Guide to Bird Window Collision Prevention. There are good estimates of the number of birds killed in residences and commercial type buildings. Loss estimates 2.1 per residence and 21 per mid-rise. The recent Klem study estimates 7 and 74 respectively. The Klem estimate is higher than the Loss estimate because Loss did not have available to him a count of the casualties that result from birds which hit a window leave no mark, fly off and die later. Klem was able to make these estimates using field testing combined with rehab mortality estimates.
I then discounted those estimates in two ways. I used 15 years for the useful life of both residential and commercial systems – which is on the low side. Second, I then assumed that the systems are about 82.5% effective. I used this figure because it is a midpoint between the 95% saved by FeatherFriendly and the 70% estimates for systems approved by the American Bird Conservancy. Thus over the period of the effective life a residential system will save about 87 bird deaths using the Klem estimates and 156 if the home feeds birds. The commercial estimate is 916 per building.
These estimates for the different type of buildings, though expressed as specific numbers, are approximate.