The Cognitive
Research Group is proud to host a seminar by Professor John Endler. Professor
Endler is visiting from Deakin University, hosted by Dr. Andrea Griffin.
TITLE: Visual tricks and illusions used by great bower birds when courting
females.
WHEN: Thursday September 8, 12-1pm.
WHERE: Psychology / Aviation Building, Keats Reading Room (AVLG17).
ABSTRACT:
Bowerbird males build and decorate bowers which are used only for
attracting mates and mating, and they steal from and destroy each others'
bowers. This and the fact that bird vision is fairly well understood
gives an unparalleled opportunity for experimenting with various aspects of
signalling in undisturbed wild birds. Using principles of bird colour vision
physiology we can show that they choose coloured objects which significantly
contrast with their own plumage, the bower and the visual backgrounds. We
can also show that the choice of colours is innovative; the idea of bowerbirds
choosing colours which elaborate their own plumage is an artifact of biases in
human vision. Great Bowerbird males make a 0.6m long bower avenue opening up to
1 m courts at each end. The courts are covered with gray and white objects and
coloured objects are displayed on or over them. The coloured objects are
outside the female's field of view until he displays them and then tosses them
outside her view again, further increasing colour contrast. The courts
consist of gray and white objects which increase in size with distance from the
female within the bower avenue and this creates forced perspective which gives
the illusion of a very regular pattern. This pattern regularity could be
a direct target of female choice but also generates further illusions with the
coloured objects. The quality of the forced perspective illusion significantly
predicts female mating preferences. Bowerbirds also create illusory
effects by painting the inside of the avenue, resulting in chromatic
adaptation. Finally, they present colours and shapes as "now you see it
now you don't", and also without repeating, which prevents other forms of
sensory adaptation. Given that almost all visual displays of almost all
animals are presented from a predetermined direction and orientation relative
to the receiver this raises the possibility that illusions may be used in
communication in a wide variety of species.
