Ducklings and other fowl
normally learn to follow their mother within a few minutes of seeing her,
through a process called imprinting. This process can allow a duckling to learn
to identify any moving object presented to it during its 'sensitive' period –
typically within the first week or so after hatching.
Scientists from the University of Oxford have shown
that newly hatched ducklings that are shown a substitute mother object with
only one eye do not recognise it when they have only the other eye available.
Ducklings and
other fowl normally learn to follow their mother within a few minutes of seeing
her, through a process called imprinting. This process can allow a duckling to
learn to identify any moving object presented to it during its 'sensitive'
period -- typically within the first week or so after hatching.
In this new
study, published in the journal Animal Behaviour, ducklings were
initially presented with either a red or a blue duck decoy, which moved in a
circular path, while wearing an eyepatch over one eye.
The ducklings
'imprinted' on this maternal surrogate, learning with this first eye to follow
the coloured decoy they had been presented with. In subsequent choice tests
over the next three hours, each duckling was presented with both the red and
blue decoys simultaneously while wearing either no eyepatch, a patch over the
same eye as in training, or a patch over the other eye -- the one that had seen
the decoy during training.
The ducklings
that made their choice with both eyes, or with the same eye with which they had
been trained, accurately preferred to follow the original decoy. But the
ducklings wearing a patch over the original eye, so that only the naive eye was
available during testing, showed no reliable preference between the two decoys.
The researchers
say the results tell us something about how birds' brains work. In most mammals
there is a large bridge connecting the two halves of the brain called the
corpus callosum. This structure allows rapid transfer of information between
the two brain hemispheres, including information arriving from the visual
system. In birds and other vertebrates, however, there is no equivalent
structure, and the direct inputs from each eye go to the opposite side of the
brain. That means information obtained with one eye has to follow more complex
anatomical routes to become available to the other.
This new
experiment shows that this anatomical difference means that when a duck gathers
visual information with one eye -- even something as important as learning to
identify its mother -- that information, in the short term, is not available
when behaviour is controlled by the other eye. For some time at least, a bird
may be visually informed with one eye and naive with the other.
Furthermore,
these two competing banks of information can cause internal conflicts. In a
second experiment, ducklings were imprinted on opposite decoys with each eye
(for example, the blue decoy with the left eye and the red decoy with the right
eye). When tested with each eye individually, the ducklings preferred the decoy
appropriate to that eye, albeit more weakly than in the first experiment -- as
if they retrieved one representation of their mother with the left eye and
another with the right eye. When tested with both eyes, they did not show a
preference, suggesting the possibility that the left and right imprints were
neutralising each other.
Professor Alex
Kacelnik of Oxford University's Department of Zoology said: 'This result
illustrates the diversity of the kinds of minds possessed by different
organisms. The mental experience of a bird is likely to be profoundly different
from our own, and we are still far from having a clear picture of it. As
mammals, the idea that when using one eye we may not be able to identify things
first seen by the other eye seems very strange, but this is probably what
happens to birds and most other vertebrates including reptiles, amphibians and
fish. Since only eutherian mammals -- that is, excluding marsupials such as kangaroos,
and monotremes like the platypus -- have a corpus callosum, it is possible that
the unified visual mind may be a mammalian innovation.'
Antone
Martinho, a research fellow in Oxford's Department of Zoology and the study's
first author, said: 'When a bird sees something with both eyes simultaneously,
each memory bank can acquire the same new information, and so the duck can act
as though the two brain halves are informed. What is startling about our
result, though, is that monocular viewing will often be the norm for many
birds, especially those with laterally placed eyes. Consequently, the situation
presented in our study -- that of a bird with two banks of differing,
unintegrated visual information -- will be fairly common.
'Most birds
live a fast-paced life. Many are primarily prey animals needing to respond to a
sighted predator at a moment's notice, all while each eye is sending different
images to the brain. Furthermore, most birds fly. It is somewhat baffling to
think that a flying bird may be acting in such a coordinated manner with two
separate banks of information in its brain vying for behavioural control.'
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