jamie
Rollerblading along the road
- Joined
- 10/16/09
- Messages
- 2,036
- Real Name
- Jamie
This is a summary of a part of a chapter from "Manual of Parrot
Behavior". The title of the chapter is "Sensory Capacities of Parrots"
and the authors are Jennifer Graham, Timothy F. Wright, Robert J.
Dooling, and Reudiger Korbel. It is a very interesting read.
As many of you know a bird's vision is from 2 to 8 times stronger than a
mammal. Birds eyes are relatively large in relation to the size of
their skull. Because of this their eyes allow a relatively large image
to be focused on their retinas. They also have a higher density of
"cones" than humans. The authors give an example of a hawk which has
300,000 cones per square millimeter whereas humans have around 147,000
cones per square millimeter. "Cones" are cells within the eyes that
detect daylight and colors. Also, in a bird's eye, nearly every cone is
represented by an individual axon to the bird's brain. An "axon" is a
nerve fiber- so essentially, each cone in a bird's eye has a direct wire
to its brain. In humans, we may have from 6 to 7 million cones, but
only a million axons in our optic nerves- meaining we have fewer light
receptors and several of those receptors all share a single wire to our
brain.
A parrot's eyeball is also flattened whereas ours are round. Their eyes
project a relatively smaller image when compared to other birds- especially birds of
prey. Also, we all know that a parrot can turn its head nearly 180
degrees to look around in all directions. This makes up for their lack
of eye movements.
Also, different from humans, a bird can directly control the dilation of
its eyes- and many of us can see this when our birds "pin" their eyes
when they are excited. Parrots often rapidly dilate and constrict their
pupils when they are being aggressive or are excited. Humans can not
willingly dilate or constrict their pupils. Birds do have "pupillary
light reflexes" but they are not the same as they are in humans.
Unlike humans, birds do not have blood vessels in their retinas.
Instead, they have a structure called a pecten which many scientists
belive noursihes retina cells and keeps them alive.
We have all noticed that when a bird is seriously studying something it
will turn its head or body sideways and focus one eye on the object of
interest. Behaviorists have found that birds have better lateral vision
than they do frontal vision and they take advantage of "monocular"
vision for that reason.
Another neat thing about birds eyes are that they are either
"tetrachromatic" or "pentachromatic" depending on the species. Human
eyes are "trichromatic". That means our vision is based on three
colors- red green and blue. Bird eyes can detect ultraviolet
light, fluorescent light, in addition to red, green, and blue light. In
fact, many scientists believe that their ability to see ultraviolet
light is related to their behaviors. Many feathers reflect UV lights
and studies have shown that UV reflection can affect mate choice. UV
reflection from feathers and skin can vary between sexes in some
species- and even though we (humans) can not tell the difference,
viaually, between a male and female in many species, a bird can. Also,
some types of fruits reflect UV light and the amount of light reflected
is indicative of the ripeness of the fruit. So, a bird can tell how
ripe a piece of fruit is and decide if he wants to eat it or not (maybe that explains
some of out picky eaters!!!
). The same is true for flowers.
Some babies have UV reflective cells in their mouths that tell their
parents where to stick their beaks at feeding time! Gouldian finches
are a great example of this.
Another interesting fact about birds is that they can detect a spatial
frequency of about 160 frames/second (or Hertz (Hz))- compared to 50 or 60
Hz in humans. That means that some "stroboscopic" effects
that humans may not be able to see ARE visible to birds. Artificial
lights often do not produce continuous light- meaning that they produce
light in very short bursts like 100-120 Hz. We can not see this but our
birds can. Also consider that many televisions refresh their screens at
a rate of 50-95 Hz, so our birds may be seeing more "choppy" motion than
we do if they are watching television with us or looking over our shuolders
when we are at the computer.
Many scientists are not sure what effects this might have on
birds. However, you can help improve your bird's welfare and living
conditions by providing full spectrum lights, normal light cycles, and
continuous emitting light sources
Behavior". The title of the chapter is "Sensory Capacities of Parrots"
and the authors are Jennifer Graham, Timothy F. Wright, Robert J.
Dooling, and Reudiger Korbel. It is a very interesting read.
As many of you know a bird's vision is from 2 to 8 times stronger than a
mammal. Birds eyes are relatively large in relation to the size of
their skull. Because of this their eyes allow a relatively large image
to be focused on their retinas. They also have a higher density of
"cones" than humans. The authors give an example of a hawk which has
300,000 cones per square millimeter whereas humans have around 147,000
cones per square millimeter. "Cones" are cells within the eyes that
detect daylight and colors. Also, in a bird's eye, nearly every cone is
represented by an individual axon to the bird's brain. An "axon" is a
nerve fiber- so essentially, each cone in a bird's eye has a direct wire
to its brain. In humans, we may have from 6 to 7 million cones, but
only a million axons in our optic nerves- meaining we have fewer light
receptors and several of those receptors all share a single wire to our
brain.
A parrot's eyeball is also flattened whereas ours are round. Their eyes
project a relatively smaller image when compared to other birds- especially birds of
prey. Also, we all know that a parrot can turn its head nearly 180
degrees to look around in all directions. This makes up for their lack
of eye movements.
Also, different from humans, a bird can directly control the dilation of
its eyes- and many of us can see this when our birds "pin" their eyes
when they are excited. Parrots often rapidly dilate and constrict their
pupils when they are being aggressive or are excited. Humans can not
willingly dilate or constrict their pupils. Birds do have "pupillary
light reflexes" but they are not the same as they are in humans.
Unlike humans, birds do not have blood vessels in their retinas.
Instead, they have a structure called a pecten which many scientists
belive noursihes retina cells and keeps them alive.
We have all noticed that when a bird is seriously studying something it
will turn its head or body sideways and focus one eye on the object of
interest. Behaviorists have found that birds have better lateral vision
than they do frontal vision and they take advantage of "monocular"
vision for that reason.
Another neat thing about birds eyes are that they are either
"tetrachromatic" or "pentachromatic" depending on the species. Human
eyes are "trichromatic". That means our vision is based on three
colors- red green and blue. Bird eyes can detect ultraviolet
light, fluorescent light, in addition to red, green, and blue light. In
fact, many scientists believe that their ability to see ultraviolet
light is related to their behaviors. Many feathers reflect UV lights
and studies have shown that UV reflection can affect mate choice. UV
reflection from feathers and skin can vary between sexes in some
species- and even though we (humans) can not tell the difference,
viaually, between a male and female in many species, a bird can. Also,
some types of fruits reflect UV light and the amount of light reflected
is indicative of the ripeness of the fruit. So, a bird can tell how
ripe a piece of fruit is and decide if he wants to eat it or not (maybe that explains
some of out picky eaters!!!
). The same is true for flowers. Some babies have UV reflective cells in their mouths that tell their
parents where to stick their beaks at feeding time! Gouldian finches
are a great example of this.
Another interesting fact about birds is that they can detect a spatial
frequency of about 160 frames/second (or Hertz (Hz))- compared to 50 or 60
Hz in humans. That means that some "stroboscopic" effects
that humans may not be able to see ARE visible to birds. Artificial
lights often do not produce continuous light- meaning that they produce
light in very short bursts like 100-120 Hz. We can not see this but our
birds can. Also consider that many televisions refresh their screens at
a rate of 50-95 Hz, so our birds may be seeing more "choppy" motion than
we do if they are watching television with us or looking over our shuolders
when we are at the computer.
Many scientists are not sure what effects this might have on
birds. However, you can help improve your bird's welfare and living
conditions by providing full spectrum lights, normal light cycles, and
continuous emitting light sources
