Sea lion recalls the past

Rio: A very clever sea lion

According to researchers at a Californian laboratory, sea lions are very logical thinkers.

A decade after initial studies, the long-term memory of a sea lion called Rio has been tested to the limit.

The 10-year retention interval is the longest for any non-human animal

Dr Reichmuth Kastak

By matching identical shapes and symbols, researchers have assessed how the animal adapts to learning the concept of sameness.

"The study that we did with Rio was the first time a non-primate animal has been tested in a long-term conceptual memory test," Dr Colleen Reichmuth Kastak of Long Marine University told BBC World Service's Science In Action programme.

Ten years after studies showed that Rio the sea lion could match like with like, researchers returned to see if the concept had held up over time. It does.

Holding up cards with numbers and letters on them, the California sea lion (Zalophus californianus) was asked to pick the two that looked alike and was subsequently rewarded for each right answer.

"She tells us by pointing with her nose," explained Dr Reichmuth Kastak.

"When she makes the correct response, she hears a tone and a piece of fish comes flying over the testing apparatus that she catches."

Rio grand

Whilst Rio's positive performance assured the scientists of the sea lion's conceptual memory skills, they were also pleased to note that the animal appears to have drawn on her memory to solve new problems.

"The life span of sea lions is only about 15-25 years. Rio is now 17 years old, so 10 years is really a significant portion of her lifetime," Dr Reichmuth Kastak said.

"The fact that she can remember a problem solving strategy and use it 10 years later tells us that, like humans, these animals develop and learn as young animals and they can remember those significant learning experiences later in life."

Whilst previous recollection studies have been carried out in monkeys, the scientists believe that Rio is the first non-primate to have been tested in a conceptual memory test over such a long period of time.

They hope that over the coming years, detailed studies of monkeys will provide further evidence to suggest that animals can use their long-term memory to adapt their behaviour.

"The 10-year retention interval is the longest for any non-human animal," Dr Reichmuth Kastak boasted.

"Rio showed good memory over 10 years and we feel confident that when primate studies are carried out that we will probably see very positive results."