Procedure in Pictures
During an experimental session, the nesting-box was replaced
by a special experimental box that consisted of two sections with
separate entrances and a movable tray with an artificial nest,
into which the nestlings were transferred.
The tray could be moved from one section to the other. The sections
were marked outside with colored stimuli attached to the front
panel of the box around the entrances.
During the experiment, from time to time the tray with the nestlings
was moved to the adjacent section, the stimuli being exchanged
on the entrances to prevent the bird from developing a position
habit.
For convenience in viewing the stimuli, a special perch was fixed
at a distance of 1.5-2 m in front of the experimental box where
the birds used to sit before making a choice.
During
the session, the experimental box was watched continuously with
field-glasses from a distance of 5-10 m. The choices of each nursing
parent were registered separately. When, in a trial, a bird flitted
from one entrance to another, only the first visit was taken into
account.
Between the experimental sessions the nestlings were returned to
their native nesting-box.
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