Collisions with windows

Many birdwatchers are aware that birds occasionally collide with windows and initial (rough) estimates suggest that as many as 100 million birds may collide with windows each year in the United Kingdom. In order to find out how accurate this estimate is, and to establish why birds collide with windows, researchers at the British Trust for Ornithology carried out research during the summer of 2004.

Some gardens are more prone to window strikes than others. By looking at things like how close bird feeders and nest-boxes are to windows, and working out whether it is reflections that are the problem, we should be able to suggest ways to minimise collisions and deaths. Figures suggest that up to a third of the birds colliding with windows die as a result. Others fly away unharmed or are only dazed. Sometimes, the only evidence that a window strike has occurred is the pattern of feather dust left on the window. Some birds produce more feather dust than others and leave a clearer imprint.

The only information we have at the moment about the potential effects of windows strikes on birds comes from the National Ringing Scheme, coordinated by the BTO. Some 11,000 ringed birds are reported to the BTO each year, half of which are found dead. Where the cause of death is known, 7% of Song Thrushes and 3% of House Sparrows (both of which are species of high conservation concern) had collided with windows. 34% of Sparrowhawks for which a cause of death was reported had flown into windows. Corresponding figures for other species include: Blackbird 7%, Chaffinch 20%, Greenfinch 9% and Robin 4%.

BTO WORK SEEKS TO FIND OUT MORE
The BTO has carried out some research into window strikes and why they occur. Observations were collected on a recording form sent out to BTO/CJ Garden BirdWatchers and preliminary results have been published in Bird Table 42. A PDF of the preliminary findings can be downloaded by clicking here. A full report on the project will appear in due course and we hope to produce a leaflet providing advice to homeowners on how to minimise the risks.

Are there things which people can do to prevent window strikes?
If window strikes are a problem then sticking silhouettes of birds of prey or spider webs (known as sentinels) to windows or putting up net curtains may help. However, we will be able to provide much better advice after the survey has been completed.

How can you treat a bird which has hit a window?
Often birds will fly off - which is great. Sometimes they die instantly, probably from a broken neck. However, on many occasions birds seem to be just stunned. Put the bird in a dark cardboard box - without food or water - and leave it in warm (but not hot), quiet place for an hour or so. Take the box outside, open the box and, if you are lucky, the bird will fly off. If the bird does not seem to be recovering, you may wish to take it to your local vetinarian, who should be able to give it the appropriate treatment.

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Page last updated 28 October, 2005

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