By Susan Milius
Hummingbirds can keep track of when a particular flower has replenished its nectar and is worth visiting again, say researchers working in the Canadian Rockies.
That knack may require that hummingbirds have parts of what’s called episodic memory, says T. Andrew Hurly of the University of Lethbridge in Alberta. When people recall episodes from their lives, they’re remembering what happened and where and when. Clocking nectar refills means hummingbirds remember at least “when” and “where,” Hurly and his colleagues say in the March 7 Current Biology.
For decades, people touted episodic memory as a uniquely human ability. However, there’s some evidence that other animals have similar mental capabilities, says Hurly. For example, a different research group found that scrub jays can remember where and when they hid perishable food (SN: 9/19/98, p. 181).
Hummingbirds also seemed as if they’d benefit from such skill, says Hurly. They burn energy fast but can’t store much fat and therefore need to eat often. The hearts of the rufous hummingbirds he studies beat 1,000 times a minute. The birds weigh only 3 grams.
To test the hummingbirds’ memory, the researchers visited the birds’ natural mountain territories. The team set out arrays of artificial flowers made from syringe tips surrounded by cardboard discs.
The researchers refilled half the syringes 10 minutes after a male drank the sugar solution, and the other half after 20 minutes. Even when keeping track of eight fake flowers, hummingbirds tended to visit the refilled flowers at appropriate intervals—about 10 minutes for quickly refilled flowers and 20 minutes for the slower refills.
