Apr. 19, 2000 While roadside restoration is touted as a way to provide more habitat for native species, living along roads can do more harm than good. Florida scrub-jays that nest along a highway die in greater numbers than they reproduce, according to new research in the April issue of Conservation Biology.
"Roadsides are death traps," says Ron Mumme of the Department of Biology at Allegheny College in Meadville, Pennsylvania, who co-authored this paper. "I think everyone recognizes that the number of animals killed by vehicles around the world is mind-numbingly large."
Figuring out how road kills affect a population is difficult for most species but can be measured precisely in Florida scrub-jays. Because the jays are easy to catch and band, researchers can reliably identify each individual in a population. And because jays are territorial and don't migrate, researchers can safely assume that adults that disappear are dead.
From 1986 to 1995, Mumme and his colleagues studied a color- banded population of Florida scrub-jays, a threatened species found only in the state's peninsular oak-scrub habitat. The researchers monitored the survival and reproductive success of jays nesting along Old State Road 8, a two-lane highway at Archbold Biological Station in Highlands County. Over the nine years of the study, 434 jays bred on 55 territories and had 527 young that fledged.
The researchers found that 15% more breeding adult jays died on roadside territories than on non-road territories (38% versus 23% per year). Moreover, on roadsides the number of adults that died was much larger than the number of young that survived, which means that the roadside population would have decreased by nearly a third each year if new jays had not immigrated there. In contrast, on non-road territories the number of yearlings that survived was 19% higher than the number of breeding adults that died.
The roadside death rate was particularly high for two groups. The first was breeders that had not lived along the road previously: up to half of them died during their first two years on roadside territories. Interestingly, after three years, the death rate dropped to 29%, close to that of breeders on non-road territories. The researchers speculate that the jays that survived this long either were inherently unlikely to be killed by vehicles or had learned to avoid them.
The second roadside group with a particularly high death rate was 30-90-day-old fledglings: three times as many died on road territories than on non-road territories. During this age range, young jays reaching independence--transition between being in nest and living independently--fly well and are very mobile.
Florida scrub-jays do not avoid roadside habitat and may even be attracted to it--they like to forage in open areas. The researchers recommend buffering Florida scrub-jay habitat from roads. "I think the best of the politically acceptable alternatives would be, oddly enough, clearing all vegetation of the right-of-way and keeping it mowed," says Mumme. "Then the jays will be able to see well and will find less food on the road.
Mumme's co-authors are: Stephan Schoech of the Department of Biology at Indiana University in Bloomington, Indiana; Glen Woolfenden of Archbold Biological Station in Venus, Florida; and John Fitzpatrick of the Cornell Labratory of Ornithology in Ithaca, New York.
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