I hadn't paid much attention to the bowerbird matter until reading the
December messages to Birding-Aus this evening. Preparatory to writing
a note about it for Worldtwitch, I did a bit of web research and
turned up some pages of interest, excerpted below. The first confirms
that the UC-Santa Barbara team have a $32,000+ grant from the National
Institute of Mental Health to study "Perceptual and Neural Aspects of
Visual Displays" in Great Bowerbirds. Perhaps the NIMH funding was the
reason for the reference to Alzheimer's Disease in the QLD
application. (The website was posted by mental health advocates
unhappy with the diversion of mental health grants to bird research.)
The second is an excerpt from the webpage of John Endler at James
Cook U. He is the UC-Santa Barbara professor under whom Lainy Day is
undertaking post-doc studies. The brief description of his bowerbird
studies would not cause one to suspect that they would involve killing
birds.
The third is a popular article on the James Cook U. website dated
October 10, 2000, entitled "Bachelor pads for birds", which describes
harmless experiments and invites property owners to assist in
providing access to bowers on their property. Again, nothing in the
article would cause one to suspect that birds were to be killed.
I have not seen a report about the bowerbird incident in the American
press and found nothing about it searching in Google.
Cheers,
John Wall
New York
http://worldtwitch.virtualave.net
------------------------
National Institute of Mental Health (NIMH)
"Perceptual and Neural Aspects of Visual Displays" $32,256
1F32MH12326-01, University of California, Santa Barbara
Using great bowerbirds, "the work proposed will investigate whether
perception of colored objects by male great bowerbirds is categorical or
continuous."
http://www.psychlaws.org/nimhreport/MissionsImpossible.htm
--------------------------------------
John Endler page at James Cook University
(2) Signal design, ambient light, signalling behaviour, and cognitive
abilities of bowerbirds. Do bowerbirds construct bowers using ornaments which
exaggerate their own plumage, maximize visual contrast on the bower, minimize
visual contrast at other times, or all three? We are investigating this and
related questions about the evolution of visual signals by quantification of
bowers and visual contrast of undisturbed bowers in 5 species of Australian
bowerbirds, and by carefully controlled ornament choice experiments. Questions
of cognition and categorical perception of colour and texture are being done
in collaboration with Dr. Lainy Day.
http://www.jcu.edu.au/school/tbiol/zoology/staff/endler.htm
---------------------------------------------
James Cook University website:
Bachelor pads for the birds
Bowerbird
October 10, 2000
THE challenge of unravelling the allure of the ultimate avian bachelor pad -
the bowerbird's bower - has led two researchers to Townsville and to James
Cook University.
JCU Biological Sciences Adjunct Professor John Endler and postdoctoral
researcher Dr Lainy Day have spent the past several years studying great
bowerbird species at locations in and around Townsville.
Their aim is to discover why male bowerbirds select particular objects when
building their bowers and what mental processes enable them to make the
correct decision about selecting these objects.
Bowerbirds' penchant for collecting objects bright and shiny, including
valuables like watches and rings, is well known. But they don't do it for fun.
Their motivation is compelling. And their preferences are very specific.
The shiny trinkets placed in and near the bower, elaborately constructed from
twigs, are just part of a very complex attempt to impress potential partners.
For, in the bowerbird world, the bower is the measure of the man.
"Bowerbirds have one of the very few communication systems where the message
is constructed rather than emitted,'' Dr Day explained. "The male bowerbird
uses his bower and the ornaments to communicate his quality.
"Females choose males and mate at the bower, but build their nests elsewhere,
raising their young on their own. The birds breed between June and December,
abandoning their bowers for the rest of the year."
But why do male bowerbirds choose their particular objects and how are they
able to shape their habitat in this way?
It seems that bowerbirds know what they like. Really know what they like.
Dr Day said the male bowerbirds studied had shown a distinct liking for the
colours green, white, grey and red, and placed objects of different colour in
different locations.
"They like to use green glass, snail shells, bits of red wire, aluminium
foil. They put the greys and whites and greens to the ends of the bowers and
the reds to one side of the bower and the perimeter of the shrub the bower has
been built under.
"If you paint an object half-grey and half-red, they put it halfway between
where they typically put grey (objects) and red (objects).''
Professor Endler has found that great bowerbirds decorate their bowers in
this manner in order to make their grey and black plumage stand out against
the background of the bower and its ornaments.
Dr Day has demonstrated that great bowerbirds are able to make very fine
distinctions between a preferred green colour which they place on the bower
and a very similar colour which they toss far from the bower. This ability may
seem unusual, but it is exactly how humans determine where to draw the line
between, for example, a color they call yellow and one they call green.
"The bands of the rainbow that humans perceive are artefacts of the way we
interpret what is really a smooth transition from short wavelengths of light
to long wavelengths of light."
This way of perceiving colour -- known as categorical perception - appears to
be shared by the bowerbird although his rainbow might look slightly different
to ours.
The importance of this type of perception is that there are very definite
boundaries between likes and dislikes and this type of strong regulation of
preferences can have dramatic effects on the divergence of preferred signals
between species and birds of the same species in different areas.
Dr Day said changes in preference could initially be arbitrary. "There are
shifts of preference that occur naturally as part of a dynamic system. Changes
can occur by mistake, or because of a change in habitat or a difference in
availability of objects. If there are no definite boundaries between likes and
dislikes, these arbitrary changes are not likely to stick.
"With categorical perception, you have very definite likes and dislikes, once
an individual or group of individuals has a different preference, it's more
likely to result in a permanent and profound change.'' Amplification of these
slight preference changes over time could explain the different colour
preferences of different species of bowerbirds.
Dr Day said results indicated that it was categorical perception rather than
just the availability of objects which explained phenomena like why bowerbirds
near North Ward and Rowes Bay have shorter bowers and liked the colour green
more than birds at Lavarack Barracks.
A further experiment would be carried out, comparing bowers in the Townsville
city area with bowers on bush properties. Birds in bush areas use less red on
their bowers than birds in the city. Is this because there were fewer red
objects available in the bush, or because of specific preferences?
Dr Day said the co-operation of property owners was being sought to provide
access to bush land with dense populations of bowerbirds.
For more information ring Dr Day on 07-4781-4292 or JCU media liaison officer
Jill Shields on 07-4781-4586 or 0417-602-359.
http://www.jcu.edu.au//office/media_releases/msg00127/msg00127.shtml
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