{"fact":"When crows were shown colored cards with different sized circles on the back, they could use the size difference to figure out a pecking order, even if the front of the cards were the same size.","context":"For 4 birds, the stimuli were colored cards with a circle of the same color on the reverse side whose diameter decreased from A to E (ordered feedback group). These circles were made available for comparison to potentially help the crows order the stimuli along a physical dimension.","source":"O. Lazareva; A. Smirnova; Maria S Bagozkaja; Z. Zorina; V. V. Rayevsky; E. Wasserman, Transitive responding in hooded crows requires linearly ordered stimuli., 10.1901/jeab.2004.82-1","index":419}