Biology Reference
In-Depth Information
Q How well do birds hear?
A Birds have more acute hearing than we do. Although audiology tests indicate that we
can hear higher frequencies than the birds tested in some experiments, the range at which
wehearbestislowerthanthatofsomesongbirds,andtheycanresolvenotesinsongsthat
aretoorapidforustoeasilydistinguish.Younghumanscanusuallyhearfromroughly20
to 20,000 hertz (Hz). (One hertz equals one vibration per second. To give you a sense of
what that means, the lowest key on an 88-note piano keyboard produces a sound at 27.5
hertz, Middle C is at 261.6 hertz, and the highest note is at 4,186 hertz.) As another point
of comparison, dogs can hear sounds in the 67 to 45,000 Hz range, while cats have the
keenest ears, capable of distinguishing sounds from 45 to 64,000 Hz.
TwospeciesofgrousefromEuropeandAsia,calledcaper-cailles,canproducesounds
below 20 Hz in their breeding displays, and North America's Ruffed Grouse drums at 40
Hz. They produce these sounds to attract mates and to defend territories from rivals. Be-
havioralstudiesshowthatpigeonscandetectsoundsaslowas0.05Hz.Thismayprovide
one of the cues that pigeons use to home, because such sounds as wind blowing over dif-
ferent kinds of terrain and ocean waves can carry over hundreds or even thousands of
miles.GreatHornedOwlsinsomelabexperimentsappeartohearbetterthanwedoatthe
lowest frequencies, but they may be perceiving these sounds through their sense of touch
asweperceivethelowestbasssoundsbyfeelingthevibrations.Grousemayhaveevolved
to produce sounds at the limits of owl hearing abilities so that they can safely display at
dawn, dusk, and night, when owls are most actively hunting, preferably for something as
large and tasty as a grouse.
Most songbirds seem to hear best in the range between 1,000 and 5,000 Hz, about the
range of the top two octaves on a piano and a bit higher. Most people can easily hear
songbirds singing at the mid-range, but as we grow older, we start losing the highest and
lowest frequencies. Some bird songs are simply too high for most older people to de-
tect without hearing aids: the sibilant trills of Cedar Waxwings in the 6,000 to 9,000 Hz
range,thesweetnotesoftheCapeMayWarblerat10,000Hz,andthelovelybutsky-high
Blackburnian Warbler songs that ascend at the end to sometimes top 11,000 Hz.
Q Do birds use sonar?
A Sonar, or echolocation, in the animal world is a method for detecting and locating ob-
jects bysending outsoundwaves that are reflected back bythe objects; it'susually found
in nocturnal creatures or those that hunt in the blackness of the ocean deep or in dark
caves.Spermwhalesusesonartofindandcatchsquidintheoceandepths,andbatsuseit
to catch insects and to avoid colliding with objects. Bats emit extremely high frequency
sounds; these ultrasound wavelengths are tiny enough to bounce off very small insects.
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