A few weeks ago I was with my wife in the Buckfast Abbey cafe after a long walk, enjoying an Earl Grey tea and admittedly a rather indulgent cake. The cafe has an external patio area with a glass screen to enable views of the grounds. We watched a pair of busy Pied Wagtails (Motacilla alba) that seemed to be enjoying chasing each other around the gardens below. Suddenly one of them hit the glass with quite a thud, rousing tea drinkers from their afternoon stupor. The bird landed on a roof below and stood almost motionless, panting with its beak wide open. It stayed like this in apparent shock for over 10 minutes and remained that way as we left.This type of occurrence is commoner than I realised. A US report claims that collisions with clear and reflective materials such as glass are the second highest man-made mortality factor for birds worldwide, only superseded by habitat destruction (Klem, 2008). This amounts to billions of deaths from head trauma; far higher than hunting, road kill, and domestic cats. There have been many prominent campaigns against hunting birds and more recently wind turbine objectors have frequently cited bird kill as an argument against their installation, and yet the far greater toll from glass gets conveniently ignored. The birds appear to treat these barriers as invisible. This type of death is no discriminator of an individual’s level of fitness, unlike more natural mortality factors. The RSPB recommends the use of silhouette images of birds of prey on windows to deter birds, particularly on large glass areas such as patio doors, or where birds might perceive a clear pathway through structures. Other solutions include netting or hanging objects in front of windows, placing feeders closer to windows to reduce the speed of impact, angling windows at 20-40 degrees also to reduce impact, and more novel use of one-way films that create patterns and shades rendering them relatively opaque (Klem, 2008).
Meanwhile at home I accidently discovered last year that my stuffed Barn Owl place on one of our deeply recessed window ledges appeared to be putting off birds coming anywhere near the back of our house – perhaps not a practical large scale solution!Klem, D (2008) Avian mortality at windows: The second largest human source of bird mortality on Earth. Proceedings of the Fourth International Partners in Flight Conference: Tundra to Tropics. 244–251