Research reveals strong memory in hummingbirds

Mind muscle | Hummingbirds can recall feeder and flower locations

A hummingbird’s brain is 7,000 times smaller than that of a human, but the tiny, mighty bird can memorize flower locations, encode geometry and track the passage of time.

Many humans can’t do as well.

So says University of Lethbridge researcher Andy Hurly, who talked about the big brains and big memories of hummingbirds during the Wildlife in the Wind lecture series March 3 organized by the Alberta Wildlife Society.

Hurly has been studying rufous hummingbirds in southwestern Alberta for 22 years.

The birds weigh about as much as two dimes, have a heart rate of 1,000 beats per minute and fly at 60 to 80 wing beats per second.

“Hummingbirds have incredibly high metabolic rates,” said Hurly.

“They are just little energy machines.”

To maintain that pace, they have to eat every 10 minutes, primarily by sipping nectar from flowers. If they are unable to do so, they fall into torpor and soon die.

But how does a hummingbird avoid wasting energy in revisiting the flowers from which it has already sipped?

“If it starts visiting empty flowers, it could easily run out of energy within a few minutes or a few hours, so the critical time frame in which hummingbirds can starve to death is surprising short,” he said.

“They live on the energetic edge all the time.”

Hurly and his team used artificial flowers containing sugar water to discover that hummingbirds remember which flowers they’ve recently visited.

They also found that the birds use geometry to navigate to particular locations and do not use flower or object colour as a guide to plentiful food sources.

Red, the predominant colour of millions of hummingbird feeders across Canada, is not as big a factor in attracting the birds as are location and the memory that food was previously there, said Hurly.

“Red flowers and red hummingbird feeders are a great way to attract a hummingbird to a location, to a flower, the first time. After that, they don’t care what colour it is. They just remember the place.”

Hurly’s tests found that even without an identifying colour marker, hummingbirds will fly within a minimum 70 centimetres of a location where they once found nectar, even if the flower is no longer there.

“That’s a very strange thing and a pretty marvelous thing, since they must be doing that not just for one flower but for many flowers,” said Hurly.

He and his team also tested hummingbirds’ perception of time by refilling four feeders every 10 minutes and four every 20 minutes. The birds quickly figured out which ones to visit more frequently, demonstrating episodic memory.

“Not only do they know that there’s 10 minute and 20 minute flowers but they remember which 10 minute and 20 minute flower they last visited,” said Hurly.

“I think that’s astonishing. I don’t know if I could do this. If I were to do this … I think I would need a pencil, paper and eight stopwatches.”

Researchers used only eight flowers in the tests, but hummingbirds could be doing calculations for dozens or hundreds of flowers at once, he added.