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Why bird feeders should be placed within 18 inches of windows

New buildings can be designed based on practices that limit risk of bird-window collisions.

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Wooden bird feeder in the form of a house in the summer forest, close-up
(Pedal to the Stock via Shutterstock)

By Mark Waghorn via SWNS

Bird feeders should be placed within 18 inches of windows to prevent potentially fatal collisions, according to new research.

It reduces the available space where they can gain speed - and suffer a potentially fatal accident, say scientists.

The problem is a major cause of bird mortality - and kills greater numbers of our feathered friends than previously feared.

The first study of its kind has found why birds fly into windows - and what happens to them afterwards.

First author Brendon Samuels, a PhD candidate at Western University, London, Ontario, said: "Bird-window collisions happen all over the world throughout the year.

"But the frequency and severity of collisions seem to be underestimated by the public, especially at residential settings.

"One reason is that collisions happen suddenly and are difficult for people to observe directly. When birds fly away afterwards, it is unclear what ultimately happens to them.

"Our findings highlight how common collisions can be in residential settings, especially where there are bird attractants like feeders."


Along with their warming tunes and chirpy personalities, but alongside their charm, birds are a vital part of the ecosystem.

However, these creatures are under threat. Windows reflect sky, clouds and trees. Up to 100 million birds in the UK strike them each year - with around a third dying.

Audio and video recordings in a residential backyard now provide the first glimpse of what happens in the moments leading up to impact.

An analysis of 29 collisions and nine near-misses showed flight velocity and angle of approach both predicted outcomes following collisions.

Faster flights at angles of approach closer to perpendicular were most hazardous. Only a small proportion resulted in an immediate fatality and were detected by occupants.

Most were followed by the bird flying away without leaving a trace. It is believed some may suffer injuries and later die far from the site.

It suggests the extent of collisions may be vastly underestimated by traditional survey methods. 

Surveys have focused mostly on larger structures such as office blocks. Yet residential buildings are the most numerous with windows.

They represent the greatest cumulative threat. New housing development is being prioritized in many parts of the world.

Appetite for large glass windows and railings continues to grow. Garden bird feeding has gained in popularity over the pandemic, drawing more birds into high-risk settings. 

The study, published in the journal PeerJ, found collisions occurred nearly as frequently with smaller windows as with large glass doors.

Samuels said: "Given birds' flight velocity prior to impact predicts the lethality of collisions with windows, we recommend bird feeders or baths should be placed within 1.5 feet to reduce the available space where birds can gain speed."

New buildings can be designed based on practices that limit risk of bird-window collisions.

Similarly, existing building windows, such as those on homes, can be retro-fitted using simple materials to add visual markers to the exterior of the glass.

Samuels said: "An important direction for future research is to characterize how birds orient their eyes to detect and avoid collisions with windows, so collision deterrents can be designed optimally to match bird vision.

"This study documented birds approaching windows from variable angles. Designs and tests of collision prevention technologies should take this into account."

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