Threatened Birds May Be Rarer than Geographic Range Maps Suggest

To: Birding-aus <>
Subject: Threatened Birds May Be Rarer than Geographic Range Maps Suggest
From: "John Leonard" <>
Date: Wed, 12 Dec 2007 21:08:48 +1100
Ii think everyone who has ever looked for an uncommon bird and been
disappointed by the optimistic range suggested in field guides will
recognise the truth of this...

John Leonard

On 12/12/2007, L&L Knight <> wrote:
> Threatened Birds May Be Rarer than Geographic Range Maps Suggest
> December 10, 2007
> By Kim McDonald
> 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, according
> to a  study published online this week in the journal Conservation
> Biology.
> "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 Walter  Jetz, an assistant professor of biological
> sciences at UC San Diego and the  lead author of the study, which will
> appear in the February issue of the  printed journal. "This suggests
> that many threatened species of birds may be  even rarer than we
> believe and are in greater danger of going extinct."
> "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," said  Cagan
> Sekercioglu, a senior research scientist at Stanford University and a
> co-author of the study. "This suggests that the  conservation status of
> many narrow-ranging, specialized and threatened bird  species may be
> worse than we think."
> 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. 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.
> The researchers' study was limited to mostly temperate areas with
> relatively high-quality data on bird distributions. They said they
> expect that in the tropics, where the majority of bird species reside,
> but where research and data  on bird distributions are more limited,
> that the problem of ounderstimating <overestimating?> bird  species'
> ranges may be even more extensive than the scientists found for
> Australia, North America and South Africa.
> "People  have been treating tropical and temperate data on bird
> distributions as if they  are of equal quality," said Walter Jetz. "But
> the overestimation is especially  large for tropical species, which
> have much smaller geographic ranges, smaller  population sizes, are
> more specialized, and are in greater danger of extinction  than those
> in temperate areas."
> Jetz and  Allen Hurlbert of the National Center for Ecological Analysis
> and Synthesis in  Santa Barbara published a related study in the August
> 14 issue of the Proceedings of the National Academy of Sciences ,  that
> found that range maps of birds less than 200 kilometers in area also
> "overestimate the area of occupancy of individual species and
> mischaracterize  spatial patterns of species richness."
> Jetz added  that range maps are becoming especially important for
> ecologists making  projections of the impact of climate change on the
> health of specific  populations and that these two studies demonstrate
> that conservationists need  to be especially careful when making
> predictions about future risks to species  during rapid climate change.
> "If we're starting with a range estimate for a population that is much
> larger than it truly is, then we have started with the wrong parameter
> for our future projections of climate change," he said. "If you've
> already started with an overestimate of the range, then there's a real
> danger in understimating the risks of extinction in future projections
> of climate change."
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John Leonard

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