JULY/AUGUST 2019. DISCOVER 49
Insects and the Origin of Flight
Found in practically every niche on all seven continents,
insects are the most successful class of animals on the
planet. But it wasn’t always like that. Roll back the clock
385 million years, and you’ll find the first bug in the fossil
record. The next insects appear a full 60 million years later
— in sudden and extreme abundance. Last year, Stanford
University researchers provided an explanation for the
population explosion: the evolution of flight.
The insects in this second wave were armed with
wings, unprecedented appendages that allowed them
to escape predators and reach new sources of food high
up in trees. It was one of the greatest of all evolutionary
breakthroughs — and vertebrates wouldn’t catch on for
another 90 million years.
Hummingbirds Versus Frigatebirds:
Two Extremes of Bird Flight
The frigatebird can fly across oceans. The hummingbird can hover
and pivot in any direction. Although both have wings and feathers,
and share a recent ancestor, their approach to flight couldn’t be
more different. The divergence reveals how flawlessly each is
adapted to its niche.
The Weird
Vortices of
Dandelion
Seeds
Dandelion seeds
should not be able
to stay aloft for
miles — but they do.
The umbrella-like
structures that carry
seeds on air currents
are made of wispy
bristles, and they’re
leaky. Only recently
have scientists
figured out that the
leakiness is the secret
to dandelions’ success
at long-distance
unpowered flight. As
air passes through
the pappus — the
technical name for
that bristly structure
— it generates a vortex
like a miniature
hurricane, and the
updraft provides a
little lift. Combined
with other aspects of
airflow, this so-called
separated vortex ring
makes the pappus
four times more
flightworthy than a
parachute, ensuring
that dandelions
continue to sprout
everywhere there’s
a lawn.
The Hummingbird
Hummingbirds can be
as small as insects —and size isn’t the only
similarity. Whereas
ordinary birds pull
themselves aloft with
just the downstroke
of their wings,
insects and hummers
generate lift in both
directions. This
ability is the
result of their
unusual avian
anatomy, with
enlarged upstroke
muscles and the
ability to invert their
wings, powering
a breathtaking
80-stroke-per-second
beat.
The Frigatebird
With a wingspan over 6 feet
and weighing less than 4
pounds, the frigatebird is
built for gliding. It can catch an
updraft under a cumulus cloud,
spiraling to a higher altitude than
some planes, and ride the winds
without flapping for over 30 miles.
Researchers have observed
frigatebirds spending monthsin the air without landing. The
endurance fliers even sleep while
aloft, in 10-second bursts that add
up to a nice, restful 40 minutes
a day.
Wings go way, way back in the fossil record.
Insects were flying tens of millions of years
before any vertebrates took to the sky.O
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CUMMINSBarbs
Extending from the rachis,
the barbs provide tail and flight
feathers with smooth surfaces
to catch the wind. In the case
of down, they also trap air for
insulation.Barbules and Barbicels
These small structures
interlock to hold the
barbs together, affording
airtightness and rigidity.
(Down feathers lack
rigidity because they
lack barbicels.)Calamus
The base of the rachis,
the calamus attaches
to a follicle in the skin.Rachis
This hollow shaft gives the
feather a strong and lightweight
central structure to support the
barbs along its edges.A Feather
Primer
Bird feathers have
multiple functions,
ranging from
flight to insulation,
despite sharing
the same basic
anatomy.