Biology Reference
In-Depth Information
Despitethedeclinesofsomeofthesespecies,thereisplentyofroomforhope.Habitat
restoration has helped Kirtland's Warbler populations increase more than ten-fold in just
three decades. Where wetlands are restored, waterfowl populations respond quickly. The
ConservationReserveProgram,conservationeasements,andotherinitiativeshavehelped
declining grassland species, too. When we set our collective will to solving a problem,
we usually succeed.
Q When I was on a local bird walk in Florida, I saw some beautiful birds that the
leader identified as Eurasian Collared-Doves. I was thrilled, but she said that they're
not native to America and so are not a “good” species! Is that true?
A
Eurasian Collared-Doves are beautiful birds and have an important place in the eco-
systems of southeastern Europe and Japan, where they are native, but they are not native
to Florida. These doves were released in the Bahamas by humans in the 1970s and had
spread to Florida by 1982. They are still most abundant near the Gulf Coast but have
spread as far as California, British Columbia, the Great Lakes region, and Veracruz in
Mexico.
So far, Eurasian Collared-Doves in America don't seem to be competing with native
species for food or nesting sites, and this introduction may well prove to be less destruct-
ive than most. But some introduced species are implicated in the declines of native birds
because they compete for nesting sites. European Starlings and House Sparrows aggress-
ively take over nesting cavities of native birds such as Red-headed Woodpeckers, Purple
Martins, and bluebirds.
Q Don't introduced birds contribute to an area's biodiversity? And isn't that a good
thing?
A
Biodiversity is the variation of life forms within and among ecosystems and is often
used as a measure of the health of a biological system. So it certainly does appear that by
adding a new species, we're adding to biodiversity.
Sadly, it's not as simple as that. Consider invasive plants: when one — such as kudzu,
purple loosestrife, Eurasian water milfoil, or cheatgrass — colonizes an area, it quickly
crowds out a variety of native plants, greatly reducing the overall plant biodiversity of
that area. That, in turn, reduces the biodiversity of animals. For example, when cheat-
grass invades rangeland in the West, it crowds out native sage grass, and so is one of the
primary causes of the dramatic decline of Greater Sage-Grouse.
Invasivenonnativebirdscandothesamething.HouseSparrows,likenativebluebirds,
wrens, Purple Martins, and Prothonotary Warblers, nest in cavities that they cannot ex-
cavate themselves. All of these species normally take over an abandoned woodpecker
hole, a cavity formed when a branch rots out, a nest box, or similar enclosed space.
