Biology Reference
In-Depth Information
centrationsofsucrose,butdidn'tseemtorespondtoglucoseatall.Inanotherexperiment,
pigeons didn't seem to have any response to quinine, and half responded to saccharin.
Birds do respond to some bitter tastes. If a Blue Jay bites into a monarch butterfly, the
strong bitter taste makes the jay spit it out. Monarch caterpillars feed on milkweed, and
foul-tasting toxins from the milkweed, called
cardenolide aglycones,
are taken up by the
caterpillar'stissues,remainingintheadultbutterfly.Thebrightorangecolorofmonarchs
protects them from any bird that tasted one and either found it too bad-tasting to eat or
swallowed it and got sick.
Extra-Sensory Perceptions
Q Do birds have a sense of touch?
A
Many songbirds have very few tactile nerve endings on their feet. Gray Jays have been
known to stand on cast iron pans where bacon is sizzling without apparent discomfort!
But birds have an excellent sense of touch that works in other ways. Beneath the feath-
ers, bird skin is very sensitive, especially where the flight feathers attach and at the wing
joints,allowingbirdstosenseandadjusttothetiniestchangesastheyfly.Thankstotheir
exquisitesenseoftouch,hawksandothersoaringbirdscanfeeltherisingairofathermal
air current to capitalize on easy lift during migration.
Furthermore, bird beaks and tongues may not have many taste buds but they do have
a great many touch receptors, as shown by the following examples.
Woodcocks, snipes, and some sandpipers have exquisitely sensitive tactile sensory re-
ceptors at the tips of their bills, providing them with the means to detect and grasp
worms more than two inches below the surface by touch alone.
Woodpeckers have dense, sensitive touch receptors at the tips of their tongues, which
they use to feel out insects dwelling deep in wood.
Finches have a great many touch receptors in their beaks and tongues, allowing them
to hold and crack open a seed shell in the corner of the beak as they deftly manipulate
and swallow the seed inside.
The bills of ducks and geese are extremely sensitive, especially at the tip and along the
outer edges. Just along the edge of the palate, a Mallard has 27 touch corpuscles per
square millimeter, which compares with 23 touch corpuscles per square millimeter in
the most sensitive part of a person's index finger.
ThebillsofWoodStorksaresosensitivethatwhenblindfolded,thesebirdscouldclose
their beaks on a live fish in as little as 0.019 seconds after first touching it; this is less
than half the time it takes for us to blink.
