A Bird in the Hand: How a Smithsonian Zoologist Spent the Pandemic Tracking Nectar-Robbing Orioles

During the pandemic shutdown, Gary Graves discovered his next research project in his own backyard

A black-and-orange orchard oriole perches on a bright red flower and uses its beak to peck at the petals.
While most nectar-eating birds stick their heads directly inside the flower, which coats their heads in pollen, the orchard oriole sometimes pierces the base of the flower with its beak to drink the nectar without getting covered in pollen. As a result, it gets the sweet reward without having to do the leg work of pollination. Gary Graves

Each day of the summer of 2020 and 2021, Smithsonian research zoologist Gary Graves went out to his backyard in the Ozark Mountains to face a familiar crime scene: the vibrant orange blooms of his trumpet creeper vine littering the ground, the flowers full of holes and torn to shreds. The perpetrator: a little flock of chestnut and yellow orchard orioles. Graves, a curator in the museum's division of birds who specializes in birds like vultures and the microscopic organisms that live inside them, documented the magnitude of daily vandalism like a forensic analysis.

When the COVID-19 pandemic hit in 2020, the Smithsonian National Museum of Natural History shut down and few museum personnel were allowed entry. At the time, Graves was in the middle of a project studying the microbiomes of vultures, but the pandemic put that project on hold. Unable to conduct his regular research at the museum, Graves journeyed to his vacation home in the Ozarks to telework, about a thousand miles west of DC.

During the summer months, he noticed a persistent pattern of birds stealing nectar from his backyard flowers. He quickly recognized this behavior as unusual and unstudied and decided his next research project would be to characterize this behavior happening right in his own backyard.

A curator and research zoologist in the museum's division of birds, Graves relocated to his vacation home in the Ozarks during the pandemic. Here, he stumbled across a new research project right in his own backyard. Mark Robbins

“I was prohibited by the museum from doing any research travel and couldn’t get permission to do field research, so I was stuck in my yard,” said Graves. “But then I thought, ‘here is something that I can do.’”

What makes nectar-robbery particularly unusual? After all, nectar’s entire purpose is to be consumed by animals. However, not all nectar sips are created equal. Graves describes three different types of nectar consumption: legitimate pollination, nectar thievery, and nectar-robbery.

The first follows the common story of pollination – an animal coevolves with a flowering plant in a way that results in a mutually beneficial scenario. The animal, such as a bee or hummingbird, pollinates the flower and receives nutritious nectar from the plant as a reward.

“And that's a nice clean story,” Graves said. “But in every system, there are always free-riders and cheaters.”

Those free-riders and cheaters are the nectar thieves and robbers. Nectar thieves are those who take the nectar without pollinating the flower but cause no harm otherwise. Flower anatomy typically fits their coevolved pollinator like lock and key, helping the pollinators live up to their namesake while enjoying their sweet nectar treat. Nectar thieves bypass this pollination system, taking the reward without fulfilling their end of the bargain.

The smallest North American oriole species, the orchard oriole splits its time between the eastern half of the United States, where they breed and lay their eggs in pouch-like nests, and Central America. Dan Pancamo, Flickr

“So a nectar thief is like a shoplifter, but a nectar-robber is someone who takes a sledgehammer to a jewelry store.”

This ruinous behavior can possibly shut down the reproductive potential of the plant. The robbers either rip the flowers off entirely or provide an easy shortcut to the nectar reward, like a borehole through the flower petals, to entice the legitimate pollinators away from doing their job.

Since the plant can’t fight back, the only defense it has is to evolve in some manner to minimize or circumvent the effects of the oriole’s nectar-robbery. 

According to Graves, avian nectar-robbery is not as well-known in North America as on other continents. The trumpet creeper observations have some neat implications in the broader field of pollination biology. So Graves took the opportunity to document it himself while in lockdown.

Due to its colorful flowers, the trumpet creeper vine attracts both gardeners and a range of pollinators like ruby-throated hummingbirds. But the gaudy plant also attracts its fair share of shady nectar thieves and robbers. Gary Graves
Every morning, Graves went out to assess the damage: how many flowers did these birds ruin? What method of destruction were they using? Did their methods change? He noted everything on a spreadsheet and did this for more than 40 days in both 2020 and 2021. Now, his paper describing the method of the mayhem appears in the journal Scientific Reports.
The aftermath of a nectar robbery: severed flower petals littering Graves's backyard. Gary Graves

The main finding Graves described was that the orioles wrought havoc on the plant’s reproduction during their presence. The birds bored holes and robbed nectar from over 90 percent of the plant’s flowers, and the plant bore no fruit until the orioles departed the region on their fall migration. Extending the flowering season past the birds’ departure date may be the only way for this population of trumpet creepers to reproduce.

Results aside, Graves feels that the paper’s main take-home message is that the opportunity for scientific discovery is everywhere. There is no need to travel great distances or have fancy equipment to make noteworthy scientific discoveries – the next discovery could be hiding in plain sight in your backyard. But like all good detectives, scientists must have an inquisitive eye.

Related stories:
How the Pandemic Changed Scientific Exploration
Get to Know the Planet’s Pollinators and More Natural History Programs This June
Meet One of the Curators Behind the Smithsonian’s 640,000 Birds