There are far fewer island scrub jays than
previously thought, a new calculation of their population size finds. The new
count makes them one of the 10 rarest songbirds in the continental United
States.
Previous work overestimated their population by
fivefold, according to the new study, published in the October issue of the
journal Ecological Applications. This overestimate was caused by incomplete
sampling, according to a statement from the Smithsonian Conservation Biology
Institute, whose scientists co-authored the study.
The striking blue
bird lives exclusively on California's Santa Cruz Island. Despite the reduced
population estimate, its numbers have grown slowly in the past few decades
thanks to the removal of non-native
pigs, sheep and cows that destroy the birds' habitat.
The study estimates that there are 2,500 scrub
jays living in the wild. The scientists counted jays at more than 300 locations
on the island and used a computer model
to fill gaps in their data. Using vegetation maps, they found the birds were
most prevalent in areas dominated by scrub oak trees.
As a result of this study, the International
Union for Conservation of Nature has changed the island scrub jay's status from
near-threatened to the higher-risk category of vulnerable, according to the
statement. Threats to the bird's small population include restricted island
range, lack of genetic diversity, West Nile
virusand loss of habitat to oak disease and wildfire.
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