Although the roadside sight of flattened fauna is familiar enough, few scientists have documented road kill's effect on populations of animals. Now researchers report that for a group of threatened Florida scrub-jays, the siren song of the open road is especially dangerous: More birds die in roadside territories than are born there each year.
The Florida scrub-jay is already in enough trouble. The birds live in a relatively restricted range of scrub oak forests in the Florida peninsula--a habitat that is rapidly losing ground to housing developments and amusement parks. Researchers concerned about the scrub-jays' future have been intensively studying the birds for more than 30 years. They record which birds breed, how their offspring fare, where they nest, and when they die.
A team of researchers including ornithologist Glen Woolfenden of the Archbold Research Station in Venus, Florida, used these scrub-jay genealogies to quantify the effects of a 55-mile-per-hour (88 km/h), two-lane country road that runs through scrub-jay territory. They compared survival rates from roadside birds with those for birds that nested near dirt fire lanes or away from roads altogether.
For scrub-jays who live away from the road, about 23% of breeding adults die each year. Birds living on the road's edge have a tougher time: About 38% of the breeding adults perish annually, the researchers report in the April issue of Conservation Biology. Youngsters that have recently left the nest are in even more danger: They are three times more likely to die than fledglings from other territories. Overall, the roadside territories act as a sink for the population: Four birds die there for every three that make it to 1 year old. Birds from other territories move into breeding areas left vacant by road-killed birds, thereby putting themselves at risk.
The authors suggest minimizing the building of new roads through scrub-jay habitat and slowing traffic speeds on existing roads. Robert Deblinger, wildlife biologist for the Division of Fisheries and Wildlife in Westborough, Massachusetts, says, "I was surprised to learn that the mortality rate is as high as it is," adding that mowing roadside vegetation might keep the scrub-jays from wandering into a vehicle's path.