How fear alone can impact birds and lower population growth
In a paper just published, Marek Allen and researchers from the University of Western Ontario address this question. They measured the effects of fear on a population of wild song-sparrows. These distant relatives of our own house-sparrow frequent bushes, gardens and roadside hedges throughout North America.
Although not everyone would approve of subjecting wild creatures to artificially induced stress, Allen and his colleagues decided to put ‘the fear of God’ into song sparrows and record its effects on them. They chose sparrows living on five small coastal islands in British Columbia for the experiment. Some song sparrows migrate, but these island ones are year-round residents.
The team broadcast "predator vocalisations at high but naturally occurring rates" to sparrows over three breeding seasons. The calls were transmitted on 54 of the birds’ territories, while vocalisations of non-predatory birds were transmitted at 51 locations.
Electric fencing and netting ensured that every nest was protected from predators so that variations in nesting performance would be down to the broadcast calls and not to other hazards. Each nest was visited daily. Video cameras provided constant surveillance.
