Lecture: Avian Senses
Vision:
Large eyes: acute vision
Good color vision (red - ultraviolet)
Position of eyes on head:
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typically a tradeoff between how far they can see around their head (needed
for predator avoidance) and how much binocular vision they have (needed
to judge distance; important for predators)
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owls: eyes focus forwards, more binocular vision (better depth perception),
less visual field
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woodcock: eyes can see far back around head - better predator detection,
high visual field.
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bitterns: eyes can see on both sides of head: large visual field.
Retina (where nerve cells are) has two centers of good focus instead of
the typical 1; allows binocular vision forward as well as large visual
field
Motion Detection:
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ability to detect motion extremely high:
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can detect movement in very slowly moving objects (15°/hour); may be
related to migration: ability to detect movement of sun, stars to use as
compass
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can detect very rapid changes from dark to light; probably related to flight
- detecting rapid changes so they don't crash
Hearing:
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acuity (range of frequency (pitch) and amplitude (loudness) that can be
detected): most species similar to most mammals
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exception: owls can detect low power (i.e. very quiet) sounds
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exception: some pigeons can detect exceptionally low frequency sounds
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birds can detect exceptionally rapid changes in frequency
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owls: can detect direction of sound extremely accurately: ear openings
at different levels, facial disk feathers focus sound
Echolocation: locate objects by emitting sounds and listening for echo
of sound (like bats) occurs in a small number of bird species
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occurs in oilbird (Caprimulgiformes) and swiftlets (Apodiformes)
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unlike bats (the best echolocators), birds use relatively low frequency
sounds to echolocate
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low frequency sounds should result in less ability to detect details through
echolocation
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however, swiftlets nest & roost in in huge colonies in completely dark
caves and can find their way back to their nest without crashing into each
other using echolocation, so it seems pretty effective
Olfaction: (smelling)
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poorly developed in most birds
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development of sense of smell extremely variable among species:
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well developed:kiwis (Apterygiformes) -- nocturnal ground feeders; nostrils
at tip of bill; turkey vultures (in Ciconiiformes) -- carrion feeders;
locate by smell; honeyguides (in Piciformes) -- can locate wax by
smell; Procellariiformes -- locate nests by smell
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moderately developed: some Columbiformes, Galliformes, Falconiformes
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poorly developed: Passeriformes; rarely respond to odors but do have some
sense of smell