Threatened birds much closer to extinction than earlier thought

December 11th, 2007 - 2:15 pm ICT by admin  

Washington, Dec.11 (ANI): An Assistant Professor of Biological Sciences at the University of California, San Diego, and his fellow researchers have opined that birds that are a threatened species, may be closer to extinction than earlier thought.
According to Walter Jetz, the lead author of the study, which will appear in the February 2008 issue of the journal Conservation Biology, geographic range maps that allow conservationists to estimate the distribution of birds may vastly overestimate the actual population size of threatened species and those with specific habitats.
Taking the example of the Pinyon Jay, an important seed disperser of North American pinyon pines, Jetz claims that 52 percent of its range is overestimated.
“Our study found that species ranges in general tend to get overestimated, but that this trend is particularly pronounced for birds that are threatened, rely on specialized diets or have small habitats,” said Jetz.
“Our findings indicate that the ranges of most vulnerable bird species are experiencing the highest overestimation, thereby painting a rosier picture of their distributions than is actually the case,” added Cagan Sekercioglu, a senior research scientist at Stanford University and a co-author of the study.
Jetz, Sekercioglu and James E.M. Watson of Britain’s Oxford University evaluated geographic range overestimation and its potential ecological causes for 1,158 bird species across 4,040 well-studied survey locations in Australia, North America and Southern Africa.
Comparing the range maps with actual bird surveys, such as those conducted by the Audubon Society, the scientists found that most species actually occur in only 40 to 70 percent of the range suggested by their range maps. In other words, these birds are not actually found in 30 to 60 percent of their supposed range.
The scientists also found range overestimation increases for species with smaller ranges and with more specialized dietary and habitat requirements.
Therefore, they concluded that range maps most strongly overestimate the distribution of narrow-ranging species and ecological specialists.
As a consequence, species threatened or near threatened with extinction are also subject to particularly high range overestimation, on average 62 percent overestimation compared to 37 percent overestimation in non-threatened species, they said.
The researchers’ study was limited to mostly temperate areas with relatively high-quality data on bird distributions.
Jetz believes that range maps are becoming especially important for ecologists making projections of the impact of climate change on the health of specific populations.
He said this latest study and another one that was published on August 14 this year clearly demonstrate that conservationists need to be especially careful when making predictions about future risks to species during rapid climate change. (ANI)

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