To even the casual observer, the similarities between bees and hummingbirds are clear. The small animals, held aloft by buzzing wings, methodically zip from flower to flower, visiting any number to collect their bounty: sweet, sweet nectar and, for some bees, pollen. It's harder than it looks, though. These animals must navigate a sea of color to get their daily fill of sugar water. They need to locate good flowers, with lots of high-calorie nectar, and waste little time with bad flowers, with little or sugar-poor nectar.
As it turns out, both bees and hummingbirds have developed similar cognitive solutions for this challenge. But it’s taken a change in perspective for scientists to see these commonalities. To do so, they’ve had to go against their instincts and treat hummingbirds as “feathered bees” despite the animals’ far-flung locations on the tree of life. (Insects and vertebrates took separate evolutionary paths at least 600 million years ago.)
That doesn’t mean the two aren’t comparable. But the historical misconception that hummingbird cognition must be “more complex” than that of lowly insects, based on an ill-conceived idea that evolution is hierarchical, has created a scientific blind spot, says David Pritchard, a postdoctoral researcher at the University of St. Andrews in Scotland. “There is no such thing as a ‘more complex animal,’” he says. Yet “people had assumed the way that bees did things and hummingbirds did things were very different.”
Pritchard is one of a new generation of hummingbird researchers turning that misconception on its head by applying methods used to study bees to hummingbirds. In some ways, these scientists are reviving work started in the 1970s, when the animals were studied together to investigate how they make decisions. In those studies, researchers aimed to identify a set of rules , like an algorithm, the buzzing animals followed to decide which flowers to visit. For example, if a flower is good, turn to the right and continue to the next flower, and if it’s bad, fly on to the next patch. “As these studies went on, the rules got more and more and more complicated to explain the behavior,” Pritchard says. Finally, the scientists conceded defeat: No simple, mechanical rules existed.
This is where the comparative work ended; from then on, hummingbirds were studied separately from bees because birds, it was presumed, were “more complex.” Scientists took hummingbirds into the lab to test their learning and memory using psychological methods, like those used to study raven and crow intelligence.
This typically involves hundreds of hours spent training birds to do odd tasks, such as peck objects in a particular order. Maria Tello-Ramos, one of Pritchard’s colleagues and co-author on a paper published this week, tried to train hummingbirds this way to study the repeated routes they travel through a familiar flower patch—what’s known as “trap-lining”—as they go from flower to flower to check the nectar in each. But no matter how many new routes she tried to drill into their heads, the hummingbirds insisted on doing things their way. "The hummingbirds weren’t having any of that," Pritchard says. "They would keep going in the order they wanted. They didn’t seem to pick up on this sequence she had trained them on."
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Tello-Ramos needed a new approach, so she decided to treat the hummingbirds more like bumblebees, adapting recent experiments that also asked how bees use trap-lines. She installed a string of artificial flowers in a valley in the Canadian Rockies, then tracked and observed individual Rufous Hummingbirds as they fed. Hundreds of potential routes through the flowers were available to the hummers, but each stuck to its favorite one or two paths.
Then she filled one of the artificial flowers with weak sugar water. Within a day, the hummingbirds tweaked their routes to avoid this bad flower—behavior that suggests hummingbirds keep track of flowers individually, and manage to remember thousands of them.
In his research, Pritchard wants to discover how they pull this off. An obvious first comparison is with a food-caching bird, like the Clark’s Nutcracker, that also must remember thousands of locations. Studies suggest that these denizens of western pine forests keep track of cached pine seeds by using prominent landmarks to wayfind, and from there calculate the distance to their various hiding spots.
So far, though, Pritchard has seen no evidence of this in hummingbirds. “When finding a location, hummingbirds seem to care more about what the world looks like at that location than distances from different landmarks,” he says. Likewise, bees are thought to keep track of good flowers by taking visual snapshots of viewed scenes. Like tiny flatbed scanners, they move their heads slowly to capture information about a given scene as they fly by. Then, when they're flying around later, they can match their view to a library of captured snapshots. Pritchard's seen hummingbirds pause to make inexplicable head movements when a food source changes, and he suspects they might capture and assess scenes in a similarly visual way.
“The eyes and brains of hummingbirds and bees are really different,” he says. “But it suggests that this kind of visual information is very useful for solving the problems these kinds of hummingbirds are solving.”
To take a hummingbird eye’s view, Pritchard is taking a page from the bee-science book, building detailed 3D models of their environments and using high-speed cameras to track head and eye movements as the birds forage. And the more he learns, the more he suspects the bee-inspired approach might be useful for understanding bird navigation beyond hummingbirds. “We know more about how an Arctic Tern makes its way between the Arctic and Antarctic than how a bird in your garden finds its way back to its nest,” he says. “Those who work with birds were too quick to dismiss the insect strategies. And new technology now means it’s a good time to revisit them.”