Figure 1.

Experimental design. (a) Photos of three different African penguins used in the experiments. Note the distinctive unique pattern of black spots on their chests, which appear at the age of three to five months and remain the same for the rest of their lives. (b) Graphical representation of the test area from an aerial view. (c) Graphical representation of the experimental procedure. First, the stimulus and focal penguins are left alone for 60 s in the test area (i). The stimulus penguin is then led out of the area by the experimenter and the focal penguin remains in the test area alone. This process took on average 21.80 ± 1.2 s (ii). Finally (iii), two contact calls (either congruent or incongruent to the stimulus penguin) separated by 10 s are played through a speaker behind the door where the stimulus penguin exited the area. The test ended 60 s after the offset of the last call in the playback sequence. (Online version in colour.)