When it comes to good recollection, elephants get the lion's share of the glory. But now an animal only slightly larger than an elephant's toenail is giving the largest land mammal a run for its memory. Hummingbirds can keep a running tab of multiple aspects of their visits to at least eight different flowers over the course of several days, displaying a type of memory once attributed solely to humans.
Previous studies have shown that birds, rats, and primates can remember where they saw of an item or event, but it's not clear whether they can remember when they saw it. The time question is especially important to hummingbirds, who must be as efficient as possible as they remove nectar from a large number flowers in their territory. Hit the same flower too soon, and it's still empty. Wait too long, and a competitor has made off with the bounty.
A team led by biologists Jonathan Henderson and Susan Healy of the University of Edinburgh in the United Kingdom set out to check the birds' record-keeping skills. Using eight artificial flowers, the scientists tested three wild, male rufous hummingbirds in the Canadian Rocky Mountains. The birds were able to recognize the difference between flowers that were refilled with nectar at 10 and 20 minute intervals, remember where the flowers were, and recall when they had last drained them.
For the most part, all three birds would return to the flowers shortly after they had been refilled, and they could accurately keep track of their visits throughout the day. The birds' performance is all the more impressive, the authors say, because they were also busy defending their territory from other males and displaying to females. The results appear in the 7 March issue of Current Biology.
"This is the first really strong evidence for timing intervals in a natural setting," says psychologist Jonathon Crystal of the University of Georgia, Athens, who does similar studies with rats in the lab. There's long been speculation that only people have a memory for unique personal experiences, he notes, which is indicative of a sense of self. If future experiments show that hummingbirds can also keep track of the quality or type of nectar, they could challenge the view that only humans have this sense, he says.