Nieuws - 27 november 2008


Birds are flying en masse to their deaths against the gleaming windows of the Forum. In last week’s Resource, two concerned students of forest and nature management reported having found eight victims over a short period. But according to ornithologist Henk Sierdsema from Alterra, this is just the tip of the iceberg.

‘One coal tit more of less, well, perhaps we shouldn’t lose too much sleep about that. But there must have been far more that the students found’, says Sierdsema, who works both at Alterra and at Sovon bird research bureau. ‘Wageningen lies at the south-western edge of the Veluwe forests, which birds migrate across, and it therefore has a large number of migrating birds.’ Sierdsema estimates that the actual death toll of birds at the Forum is ‘at least ten and perhaps a hundred times as high’. It’s just that we don’t find most of them, as they make an easy snack for cats and other predators.

‘Unfortunately, there’s a fashion for bigger and bigger surfaces of reflective glass’, says Sierdsema. ‘And still, very little thought is given to the effect on birds.’ The scale of the problem is clear from an American study of the causes of death among birds. In the United States, one billion birds fly to their deaths against window panes every year.’

The problem is that the birds just don’t see the glass itself or the room behind it. What they do see is the reflection of trees, water and air. The society for the protection of birds sells the familiar bird stickers to signpost the accident black spots. ‘But they have to be placed no more than thirty to fifty centimetres apart. So you need quite a lot for a building like the Forum’, says Sierdsema. What’s more, it is doubtful whether they work. ‘The more birds get used to flying through narrow entrances, the less effect stickers have.’

It’s better to look for a solution that involves movement, such as strips of aluminium that flap in the wind. ‘Or opaque foil of the kind that is used for billboards’, says Sierdsema. ‘A type has been developed that people inside the building can see through.’
Another option is special glass with a structure that birds can see as they get near it. But that is very pricey.