International Journal of Comparative Psychology

Although California sea lions ( Zalophus californianus ) are capable of forming complex mental concepts, they have failed to demonstrate mirror self-recognition, a skill that requires both a mental representation of one’s physical features and knowledge of a reflective surface.  Many non-human species that do not recognize themselves in mirrors can nonetheless learn to use mirror reflections to locate and retrieve objects.  A total of 7 sea lions housed at 2 separate facilities were tested on their ability to detect an object using a mirror.  The results of a preliminary detection task in which sea lions were reinforced for looking at a mirror to locate an object suggested that 4 sea lions reliably learned to locate an object positioned below a mirror in one of three locations.  A follow-up study was conducted to determine if 3 different sea lions could learn the task without training the animals to use the mirrors.  Two of the 3 sea lions located a single object in 1 of the 3 locations statistically above chance when the mirrors were added to the task for the first time.  With additional mirror exposure, 1 sea lion successfully achieved 100% accuracy in detecting familiar objects placed in 1 of 3 familiar locations.  This sea lion also demonstrated her ability to detect an object via a mirror located in a novel, fourth position with 100% accuracy.  When two novel objects were tested with four locations, the sea lion again performed well, detecting the objects 87.5%.  The results suggest that sea lions have the ability to use mirrors to locate an object with minimal exposure to a mirror, but likely need additional experience with mirrors to efficiently use the properties of these reflective surfaces and understand that the image is a two-dimensional representation of a three-dimensional object.