SAT Reading Practice Test 7

This passage is adapted from Patricia Waldron, “Why Birds Fly in a V Formation.” ©2014 by American Association for the Advancement of Science.

Anyone watching the autumn sky knows that
migrating birds fly in a V formation, but scientists
have long debated why. A new study of ibises finds
that these big-winged birds carefully position their
5 wingtips and sync their flapping, presumably to catch
the preceding bird’s updraft—and save energy
during flight.
There are two reasons birds might fly in a
V formation: It may make flight easier, or they’re
10 simply following the leader. Squadrons of planes can
save fuel by flying in a V formation, and many
scientists suspect that migrating birds do the same.
Models that treated flapping birds like fixed-wing
airplanes estimate that they save energy by drafting
15 off each other, but currents created by airplanes are
far more stable than the oscillating eddies coming off
of a bird. “Air gets pretty unpredictable behind a
flapping wing,” says James Usherwood, a locomotor
biomechanist at the Royal Veterinary College at the
20 University of London in Hatfield, where the research
took place.
The study, published in Nature, took advantage of
an existing project to reintroduce endangered
northern bald ibises (Geronticus eremita) to Europe.
25 Scientists used a microlight plane to show
hand-raised birds their ancestral migration route
from Austria to Italy. A flock of 14 juveniles carried
data loggers specially built by Usherwood and his lab.
The device’s GPS determined each bird’s flight
30 position to within 30 cm, and an accelerometer
showed the timing of the wing flaps.
Just as aerodynamic estimates would predict, the
birds positioned themselves to fly just behind and to
the side of the bird in front, timing their wing beats
35 to catch the uplifting eddies. When a bird flew
directly behind another, the timing of the flapping
reversed so that it could minimize the effects of the
downdraft coming off the back of the bird’s body.
“We didn’t think this was possible,” Usherwood
40 says, considering that the feat requires careful
flight and incredible awareness of one’s neighbors.
“Perhaps these big V formation birds can be thought
of quite like an airplane with wings that go up and
down.”
45 The findings likely apply to other long-winged
birds, such as pelicans, storks, and geese, Usherwood
says. Smaller birds create more complex wakes that
would make drafting too difficult. The researchers
did not attempt to calculate the bird’s energy savings
50 because the necessary physiological measurements
would be too invasive for an endangered species.
Previous studies estimate that birds can use
20 percent to 30 percent less energy while
flying in a V.
55 “From a behavioral perspective it’s really a
breakthrough,” says David Lentink, a mechanical
engineer at Stanford University in Palo Alto,
California, who was not involved in the work.
“Showing that birds care about syncing their wing
60 beats is definitely an important insight that we didn’t
have before.”
Scientists do not know how the birds find
that aerodynamic sweet spot, but they suspect that
the animals align themselves either by sight or
65 by sensing air currents through their feathers.
Alternatively, they may move around until they find
the location with the least resistance. In future
studies, the researchers will switch to more common
birds, such as pigeons or geese. They plan to
65 investigate how the animals decide who sets the
course and the pace, and whether a mistake made by
the leader can ripple through the rest of the flock to
cause traffic jams.
“It’s a pretty impressive piece of work as it is, but
70 it does suggest that there’s a lot more to learn,”
says Ty Hedrick, a biologist at the University of
North Carolina, Chapel Hill, who studies flight
aerodynamics in birds and insects. However they do
it, he says, “birds are awfully good hang-glider
80 pilots.”