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7/28/2019 Neurosensory System
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Avian Sensory Systems
Sensory world similar to ours, that of other
primates, primarily visual
Are some subtle and some significant
differences
Senses of birds are NOT well understood
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Vision
In most species, primary sense used to
locate, identify and obtain food Primary sense in predator detection
Important in flight, displays
(communication)
Map of world is visual
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Key Structural Components of
the Avian Eye
Lens: focuses light on retina
Retina: image-forming region
Pectin: supplies O2, nutrients to retina
(a significant difference)
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Visual acuity of birds is NOT
well understood Cones more dense: +
Flat eyes: - (some have round eyes)
Each cone has own nerve fiber: + Steep fovea magnifies image: +
Steep fovea distorts image: -
Guess: most birds slightly better than us, afew much better
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Other Features of Avian Vision
Steep fovea enables birds to follow moving
objects well (pursuit of prey)
Eyes located on side of head, many birdshave only one fovea per eye, lack binocular
vision, lack depth perception
Birds have a wide field of view (3000+common, up to 3600 in Woodcock)
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Binocular vision of owls: 2 fovea
per eye, eyes located in front
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More Features
Species with 2nd fovea (located inside edge
of the eye) have binocular vision (raptors,
aerial hawkers)
Color vision NOT well understood due to
presence of oil droplets
Richer, see ultraviolet
See better through glare, at dawn
Detect polarized light
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One more feature: better
accommodation due to musclesworking on lens and cornea
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Hearing: Total range of
frequencies heard by birdssimilar to us, but each bird
species has narrower range
Species hear best the frequencies of
their own calls and song
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Ear Structure
No external flap, rim around openingamplifies sound in species hunt by sound
Ear drum separates outer, middle ear (likeus), single bone in middle ear transferssound to inner ear (3 bones in us)
3 fluid-filled canals for balance next tomiddle ear
Sound receptors in cochlea of inner ear
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Features of Avian Cochlea
More dense sensory hairs suggest moresensitivity (types determine frequencies
heard, number stimulated determinesintensity perceived)
Tissue as well as fluid above sensory hairssuggests better temporal resolution, ability
to detect complexities of song
Experimental tests do not support
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Owls and harriers use sound to
locate prey
Rims around earopenings amplifysound
Round heads collectsound
Asymmetric ears (both
horizontally andvertically) enablelocalization of sound
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Echolocation
Occurs in 2 families, oilbirds and cave swiftlets Low frequency sounds (clicks) enable
orientation in dark caves
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Birds have olfactory organ, but
sense smell NOT well understood Turkey vultures, tubenoses,
honeyguides use locate food
Some tubenoses use to locate burrows Kiwis use to detect food underground
Use unknown in most species
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Birds have taste buds, but use ofsense of taste NOT well
understood
Birds use vision or touch, not taste,
to identify food
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Sense of touch (tactile)
Herbst (and other) corpuscles aremechanoreceptors
Located on filoplumes, bristles
Located on bills (especially probers),
tongues (woodpeckers) of some speciesfor prey detection
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Other senses of birds
Magnetic sense
Sensitive to changes in barometric pressure
Hear infrasound (super-long wavelengths)
All are foreign to us, used in migration
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Features of Avian Brain
Large optic lobes, small olfactory lobes
Large cerebellum
Site of higher learning centers, complex
neural processing is corpus striatum (middle
cerebrum), not cerebral cortex (outer
cerebrum) Left hemisphere dominance
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The Control System
Consists of nervous and hormonal systems
Elements of the hormonal system: adrenal,
thyroid and pituitary glands and the gonads Hypothalamus (midbrain) controls the
hormonal system
Neurosecretions act on adjacent pituitaryHormones from pituitary control other
glands
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Avian intelligence
Many birds have complex social memories,aware of relationships to others (cooperative
breeders, other social species) Some birds have well developed spatial
memories, can remember thousands oflocations (corvids, chickadees; parrots)
Parrots demonstrate cognitive abstractreasoning, semantic signaling (others?)