Science - March 20, 2012

Breeding birds stand their ground

Brooding birds are not easily chased away. And certainly not by a couple of roaring motorbikes on a racing circuit.

Alterra and SOVON Bird Research Netherlands have now demonstrated this with a study of the influence of noise from motorcycle races at TT circuit Assen on nature in the nearby Witterveld. This large nature area (482 hectares) sits right next to the racing circuit and is managed by Defence. It is frequented by more than 75 species of bird, very many of which appear on the Red List.
The scientists studied the effect of two races in the April-June period in 2010 and 2011 on breeding birds in the area. Surprisingly enough, there turned out to be no fundamental effect. Apparently brooding birds aren’t that bothered by a three-day motorcycle racing event just round the corner. 'Personally, I’m not surprised,’ says René Henkens, the Alterra researcher who was involved. 'We are talking about brief bursts of noise over just three days. Evidently, that’s not enough to make birds abandon their brood.' It’s largely a question of energy, believes Henkens. The later in the breeding season, the more energy that’s been invested. 'So it’s all about the timing of the event. Birds are probably more susceptible to being disturbed while they are securing their territory early in the breeding season.'
Tipping point
'By the way, we aren’t saying, go ahead and race as much as you want,’ adds Henkens. 'Of course, there’s going to be a tipping point at which the birds won’t put up with the noise. But it is unclear what that threshold level is. And we can’t ask the birds.' According to Henkens nature is often less fragile than many people are inclined to think. 'My message is this: if possible, first monitor instead of prohibiting as a precautionary measure.'
The study was commissioned by the TT circuit. The circuit’s management had acquired a licence to hold an extra car or motorcycle racing event in the breeding season on the condition that the effects were clearly mapped. The event meanwhile has bitten the dust.
Are brooding birds disturbed by the noise of racing events? Alterra report 2288