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| ‘Insights’
presents stimulating questions about bird behaviour and
is designed to develop an awareness of the complexity
of bird life.
It is difficult to
provide concise answers to the questions below as many
factors combine to help us determine bird behaviour.
But to get the ball rolling, here are some insights
to ponder. Perhaps readers would like to propose extra
reasons and details that might help form plausible answers.
Please feel free to e-mail
your answers
and also pose new questions.
This page will be updated periodically.
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What is
a bird’s eye view?
Who knows for sure
what birds see? The complex anatomical arrangement
of a bird’s eye and the remarkable processing
ability in its brain and the fact that its image
acuity is an adaptive trait make avian vision
an absorbing study. Here we describe, albeit somewhat
simply, some features to consider when thinking
about how birds see.
Among birds, raptors
have exceptionally keen eyesight. They are able
to resolve details at distances 2.5 to 3 times
further than humans — an impressive feat.
They also have binocular vision (their binocular
overlap is between 35 and 50%), which gives them
acute depth perception — useful when they
perform quick manoeuvres while chasing prey.
In many birds,
the huge number(between 400,000/mm2 and 1 million/mm2)
of light receptor cells in the retina (highest
number
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located specifically
in the central and temporal foveae) makes it possible
for birds to see sharp images regardless of the
direction and intensity of the light source. In
addition, the muscles of the eye that control
lens curvature and the aperture of the pupil permit
pin-point focusing and fast tracking as well as
quick adjustment to varying light conditions.
Various studies indicate that, in some birds,
visual information gathered from each eye and
processed in the brain might be used for different
tasks. Many birds are also capable of seeing in
the UV spectrum — an ability humans lack.
Spend some time watching
a bird in search of prey; note the position of
the eyes in the skull and their size, the posture
of the bird, its head movements, the position
of the head when the bird flies, and its foraging
environment. Look at a variety of species in this
manner. Gather as many contextual clues as possible
to help you understand how they perceive the world.
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Why
do birds join mixed species flocks?
At a glance it would
appear that the two species, pictured left, join
forces to forage together to exploit nectar-rich
resources. But could there be any other benefits
that might bring these two species together?
To find out, watch
what each species does when it alights in a tree.
Follow closely a few individuals of each species
and note whether both species forage; if so, do
their foraging styles differ? Other things to
note include the age of the birds, their position
in the tree (is there partitioning of resources?),
the tree’s proximity to other flowering
trees, the time of day, the state and similarity
of their plumage, the calls that they emit, their
response to other flock members’ calls or
body postures and how frequently they check their
surroundings. Are there dominant individuals and
if so how do other flock members respond to them?
Are there predators about?
An astute observer
will learn much from this exercise.
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| What provokes
early morning bird song?
Many song birds sing
early in the morning. The factors that influence
this phenomenon may be broken up into three categories:
1) environmental conditions, e.g. humidity, temperature,
light levels, wind speed, environmental noise,
prey activity; 2) mood of the bird, e.g. its hormonal
levels, its health, its energy budget and 3)social
interaction, e.g. proximity of neighbours, presence
of potential mates and rivals and raptor presence/absence.
Listen to specific birds as they sing in the early
morning (kookaburras are among the first to commence
the dawn chorus). Write down all that you know
about them and think about some of the factors
that might be influencing their singing. Can you
think of others? |
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Why do
magpies strike this pose?
The answer to this
question is fairly easy; however gaining an insight
into how this behaviour might have evolved is
exciting and challenging. When reflecting on your
answer, consider such contextual clues as the
size and shape of the magpie’s beak, its
diet, its foraging strategies, its predators and
territorial competitors, where it lives, and its
social behaviour. Is it a migratory species?
We all know that magpies
are territorial, frequently staking a claim that
may include manicured suburban lawns or parklands
—perfect sites for bird watching (you don’t
have to travel to enjoy the mysterious life of
birds!).
Enjoy some time in
your garden or local park and unravel the complexity
of magpies and their foraging and prey capture
strategies.
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