An understanding of Piagetian liquid conservation was investigated in four Grey parrots (Psittacus erithacus), their ages ranging from initially less than 1 year old to 18 years old. They were tested in several conditions: on the ability to choose between (a) identical containers filled with a greater or lesser quantity of a desirable liquid to see if they would reliably take the larger amount and (b) equal quantities of liquid that were visibly or invisibly transferred from identical to different-sized containers to examine their abilities with respect to conservation. Invisible transfers examined the extent to which birds chose based on perceptual evaluations of quantity and the effects of task order on their decisions. Adult birds succeeded on all or most aspects of the tests. As a chick (~6 months), 1 bird was unable or unwilling to choose between the smaller and larger quantities in the first stage of testing, but upon reaching juvenile status succeeded in all aspects of the tests. Grey parrots thus demonstrate some understanding of liquid conservation.
