LIFE & EVOLUTION
Arctic grows riskier for ground nesters
Warming may be boosting predator attacks on shorebird eggs
LIFE & EVOLUTION
wings thwart bats
interfere with echolocation
BY SUSAN MILIUS
Climate change may be flipping Arctic
neighborhoods into killing fields for
Every year, shorebirds migrate thousands of kilometers from their southern
winter refuges to reach Arctic breeding
grounds. But what was once a safer region
for ground-nesting birds now has higher
risks from predators than the tropics do,
says Vojt;ch Kubelka, an evolutionary
ecologist at Charles University in Prague.
Kubelka had heard about regional
studies of how predator risk changes by
latitude. He, however, wanted to go global.
Shorebirds make a great group for a large-scale comparison, he says, because there’s
not a lot of variation in how nests look to
predators. A feral dog in the United States
and a fox in Russia both creep up on some
variation of a slight ground depression.
Kubelka and colleagues crunched
data from decades of records of predator attack rates on about 38,000 nests of
sandpipers, plovers and other shorebirds.
BY JENNIFER LEMAN
Some moths aren’t so easy for bats to
detect. The cabbage tree emperor moth
has wings with tiny scales that absorb
sound waves sent out by bats looking for
food. That absorption reduces the echoes
that bounce back to bats, allowing Bunaea
alcinoe to avoid being as noticeable to the
nocturnal predators, scientists report
online November 12 in the Proceedings
of the National Academy of Sciences.
“They have this stealth coating on their
body surfaces which absorbs the sound,”
says Marc Holderied, a bioacoustician at
The study zeroed in on 237 populations
from a total of 111 species at 149 places
On average, these bird species lost
about 43 percent of their nests to predator attacks before 1999, but that number
has since reached 57 percent, the team
says in the Nov. 9 Science. The most
dramatic upward swoop came from the
Arctic. There, that number rose from
about 40 percent in the last century to
about 65 or 70 percent since 1999. Tropical perils in the Northern Hemisphere
the University of Bristol in England.
Bats sense their surroundings using
echolocation, sending out sound waves
that bounce off objects and return as
echoes. Cabbage tree emperor moths,
having no ears that might alert them to
a predator, have evolved scales of a size,
shape and thickness suited to absorbing ultrasonic sound frequencies used
by bats, Holderied and colleagues found.
The team shot ultrasonic sound at a
single, microscopic scale and observed
it transferring sound wave energy into
movement. The team then simulated the
process with a 3-D computer model that
showed the scale absorbing up to 50 percent of the energy from sound waves.
It’s not just scales that aid moths
that lack ears. Some other species have
sound-absorbing belly fur, the same scientists report in the September Journal
of the Acoustical Society of America.
Climate change may be spoiling the Arctic as a
save haven for ground-nesting shorebirds like
these spoonbill sandpipers.
changed “only modestly,” from about 50
to about 55 percent.
The growing dangers to nests fit with
climate change trends, the team found.
Biologists have discussed the idea that
migrating toward the poles to breed was
a way to escape the tropical abundance of
snakes, rodents and other egg lovers.
But rapid Arctic warming might have
discombobulated some predator-prey
relationships, says coauthor Tamás
Székely, a conservation biologist at
the University of Bath in England. For
example, arctic foxes used to get much
of their nourishment from rodents.
Skimpy snow cover in warmer winters
doesn’t insulate rodents as well as it used
to, resulting in shrinking rodent populations. So foxes may be shifting more to
eggs and nestlings.
That scenario sounds “highly probable,” but may be just part of what’s going
on, says Dominique Fauteux, an ecologist at the Canadian Museum of Nature
in Ottawa. A 2010 study suggested that
nest predation in the Canadian Arctic
was still lower than in temperate areas.
There may be some global pattern, but
on the ground, Fauteux says, “there
clearly are nuances.” s
For moths with ears, defenses can
include swerving out of a bat’s way.
Some moths produce toxins. Having
sound-absorbent fur or scales “might
require a lot less energy,” says Akito
Kawahara, an evolutionary biologist at
the Florida Museum of Natural History
in Gainesville. “It’s a very different kind
of passive defense system.” s
Cabbage tree emperor moths have wings
covered in tiny scales (one shown in this
confocal microscopy image) that help absorb sound sent out by echolocating bats.