CALIFORNIA sea lions may have the best memory of all non-human creatures. A female called Rio that learned a trick involving letters and numbers could still perform it 10 years later 鈥� even though she hadn鈥檛 performed the trick in the intervening period.
Learning concepts such as 鈥渟ameness鈥� 鈥� when one letter or number matches another, for example 鈥� is thought to require sophisticated brain processing. So scientists expect animals to have trouble retaining the ability over long periods unless they are given repeated reminders of the rules. Primates like the rhesus macaque have been found to have impressive long-term memories, but Rio trumped them all.
Colleen Kastak and Ronald Schusterman, marine biologists at the University of California, Santa Cruz, began training her in 1991. They started by holding up a card with a number or letter on. Rio was then shown a card bearing the same symbol and another card with a different symbol. If she picked the matching symbol, she was rewarded with a fish. Last year, the researchers tested Rio again, this time using numbers and letters not used in the previous test. She was just as good at the test as before.
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Because the symbols used were different this time, it proved Rio had remembered and was capable of applying the concept of 鈥渟ameness鈥� to new situations, rather than just recalling matches between familiar numbers and letters (Animal Cognition, DOI: 10.1007/s10071-002-0153-8).
In a second test, the researchers taught Rio to distinguish between numbers and letters. They showed her two cards at a time, one of a letter and the other, a number from a set of 10 letters and numbers. When she picked numbers she got a fish. When tested a year later, Kastak and Schusterman found Rio remembered how to separate the symbols into letters and numbers.
Kastak says their impressive memory could help sea lions recognise different categories of prey that are only present at certain times of the year.