Erroneous Feeder Placement Advice: 30 Feet Is Actually Less Safe.
Dr. Daniel Klem, who performed the basic research related to feeder placement, has explained that placing a feeder beyond 30 feet is not a safe distance. In fact the risk of death increases the further the feeder is from the window? Why? The birds do not identify a black space as glass; they perceive it as empty space. The further away from it that they start the faster they are flying when they hit the window.
My studies have repeatedly revealed that beyond one meter (3,3) there is really no safe distance to place an attractant away from the window surface. Many writers addressing the issue of where to place feeding stations near windows have wrongly interpreted the results of our feeder placement experiment to mean it is safe to place attractants greater than 10 m (33 ft) from a window surface. In designing the experiment, I placed a 10 m limit on feeder placement, thinking that this distance would be the farthest acceptable to most homeowners or wildlife park visitor center managers, because anything greater would not bring the visiting birds close enough to be seen. What our experiments and countless other observations reveal is that, except for within one meter (3.3 ft) of the glass surface, placing attractants at distances greater than 10 m (33 ft) is no safer than closer locations, as long as birds are attracted to where windows occur. Birds are at risk of a lethal strike if they can enter the danger zone from any distance from the window surface.
Source: Solid Air, Dr. Daniel Klem, Hancock House 2021, p.108.