Figure 1.

Experimental apparatus for examining foraging efforts, running distance (A,B), and number of pecks (C). (A) One-lane I-shaped maze equipped with a pair of terminal feeders. Terminal walls of the maze were colored red and blue. The feeders supplied grains of millet according to a variable interval schedule. One grain was supplied at one time in the single-chick condition (left), and two grains were supplied at one time in the paired-chicks condition (right). Note that the paired chicks were competing over food, whereas the single chicks were not. (B) Two-lane I-shaped maze. Chicks and feeders were separated by an opaque (left) or a transparent (right) wall. In the transparent wall condition, the feeders were either separated or shared. Note that the paired chicks in the shared feeder condition were competing for food, whereas chicks in the other condition did not. (C) The 2-lane maze was equipped with a fixed feeder and a variable feeder. The food tray of the fixed feeder was made of a plastic plate with 25 holes (5 × 5), each 1.5 mm deep. The food tray of the variable feeder was either a sponge or plastic plates of variable depth (ranging from 1.5 to 2.3 mm). Supplied grains tumbled into the holes, making it difficult for chicks to obtain the grains. The deeper the holes were, the more difficult it was for chicks to obtain the grains. Trays of the variable feeder were sequentially replaced in an order from the easy sponge to the more difficult plates every ca. 3 min. See text for details.