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superseded by habitat destruction (Klem, 2008).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