If visual asymmetry is valuable and triggered by pre-hatch
light stimulation, we expect breeding parents to stand up and
leave their clutch often enough to enable light exposure to the
eggs. Since this critical prediction has to our knowledge never
been studied under natural or semi-natural conditions, it is the
focus of the presented study. In view of the fact that visual asymmetry
in pigeons is morphologically manifested in the tectofugal
visual system and since retinal fibres reach the optic tectum on
the 14th day of incubation, starting to make synaptic contacts
with E15 (Manns and Gunt ¨ urk ¨ un, 1997 ¨ ), specific attention will
be given to the behaviour of the parental pairs between the 14th
and the 17th day of incubation, the last number being the time of
hatch. Since both parental animals participate in breeding, a very
short duration of light exposure is to be expected during relieves.
Moreover, these periods could be extremely small, if both adults
simply swap breeding positions instantly. Such a very short time
span would also prevent cooling of the eggs as well as the clutch
being freely exposed to predators. For our hypothesis to be correct,
however, we would expect that pigeons leave their clutch
for slightly longer periods to enable the establishment of visual
asymmetry