[TN-Bird] Birds and Noise Pollution
- From: "Charles P. Nicholson" <cpnichol@xxxxxxxxxxxxx>
- To: tn-bird@xxxxxxxxxxxxx
- Date: Mon, 27 Jul 2009 17:21:32 -0700 (PDT)
Anyone who has studied birds for a while has likely noticed that different
birds (like different humans) respond to ambient noise in different ways. The
following article from
http://sciencenow.sciencemag.org/cgi/content/short/2009/723/3, published by
AAAS, reports on an interesting new study of this.
Chuck Nicholson
Norris, TN
Pump Up the Volume. Some Birds Don't Care
By Cassandra Willyard
ScienceNOW Daily News
23 July 2009
Anyone who has woken to a cacophony of squawks and chirps knows that
birdsong, no matter how melodious, isn't always a welcome sound. Past
research suggests that birds aren't keen on human din either. But a new
study finds that not all birds think alike: Some species actually
appear to seek out noisy environments.
Among birds, noise does more than annoy. It can hinder their ability to
communicate. In fact, some scientists suspect that noise pollution is
at least partly responsible for the decline of bird populations.
Researchers, however, have had a hard time teasing out the impacts of
noise from the impacts of other noise-associated factors, such as
traffic and development.
To sort out whether noise alone can affect bird nesting and
reproduction, community ecologist Clinton Francis of the University of
Colorado, Boulder, and his colleagues spent three summers in the
pinyon-juniper woodlands of northwestern New Mexico. They located nests
belonging to a variety of bird species on 18 wooded plots adjacent to
natural gas extraction wells; they then followed those nests throughout
the summer to see whether the hatchlings fledged. The study plots were
nearly identical except for one key difference: Half of the natural gas
wells had compressors so loud the researchers had to shout to be heard. The
other half were quiet.
Contrary to the findings of previous studies, which were unable to
separate the impact of noise from other confounding variables, the
researchers found no difference in bird density: Noisy sites contained
as many nests as quiet sites. The team did, however, see differences in
species richness. Quiet sites had 32 bird species nesting on them
compared with 21 species at noisy sites. Mourning doves and
black-headed grosbeaks tended to nest on quiet sites, while
black-chinned hummingbirds and house finches seemed to actually prefer
noisy sites. Ninety-two percent of hummingbird nests and 94% of house
finch nests were located on study plots near compressors. "That was
really surprising," says Francis, whose team reports its findings online today
in Current Biology. "We haven't found any evidence in the literature showing
that species will actually select for these really noisy sites."
Of course, it's also possible that these birds were being forced out of
quiet sites, but Francis thinks that's unlikely. His team didn't
observe many species that would compete with black-chinned hummingbirds
nesting on quiet sites, and house finches succeed almost everywhere.
One possible explanation for the differences is that noise may be
hampering communication among some birds but not others. Black-chinned
hummingbirds, for instance, communicate in higher frequencies that may
still be audible against the low-frequency rumble of the compressor.
And house finches can converse in a wide range of frequencies. The two
species associated with quiet sites, on the other hand, communicate
using lower frequencies that may be drowned out by the compressors.
Ornithologist Wesley Hochachka of the Cornell Lab of Ornithology offers
another alternative: Perhaps the species found nesting near compressors
simply can't hear the racket. "We really don't know how birds perceive
what we would call a noisy environment," he says.
Nest predation may have played a role as well. Francis and his
colleagues found that a common nest predator--the western scrub
jay--avoided noisy areas. As a result, birds living on those sites had
more successful nests. Nearly a third of nests in quiet areas failed to
produce any fledglings compared to only 13% of nests on noisy sites.
On the other hand, noise could also make birds more
susceptible to predation, notes behavioral ecologist Gail Patricelli of
the University of California, Davis. When her graduate student needed
to capture sage grouse last year, she took a boom box into the woods
and played music by the group Nine Inch Nails. The noise allowed the
student to "walk right up to these birds with a spotlight and put a net
over their heads," says Patricelli. "They were sort of stupefied."
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