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The surprising science behind hummingbirds and flowers

Do they have a “type,” or it is just economics?

Guest Blogger —  October 30, 2018 — 4 Comments

Fast and graceful, hummingbirds flit from flower to flower—but which ones and why? A Chicago Botanic Garden scientist and his collaborators recently made some unexpected findings on the subject.

It’s a common perception that plants are perfectly matched to their pollinators and that each pollinator has a specific flower type that they are attracted to. For hummingbirds, many gardeners and scientists alike have long assumed their flower type to be one that is strikingly red, tubular, and scentless.

Flowers that are often thought of as typical choices for hummingbirds:

Wyoming paintbrush (castilleja linariifolia)

Wyoming paintbrush
Castilleja linariifolia

Giant red paintbrush (castilleja miniata)

Giant red paintbrush
Castilleja miniata

Scarlet gilia (lpomopsis aggregata)

Scarlet gilia
Ipomopsis aggregata

It’s not hard to see why anyone might assume that hummingbirds and certain kinds of flowers are perfect matches. Hummingbird visits to flowers are visually striking, and many casual observations suggest a typical and consistent set of floral characteristics associated with this plant-pollinator interaction. The vibrant red or orange color of blooms appear as if they were designed specifically to attract the eye of hummingbirds. A hummingbird’s long bill appears perfectly matched for the extraction of nectar from the long, tubular flowers. But don’t be fooled—while it’s satisfying to organize flowers and pollinators and their interactions into clear-cut categories (known as pollination syndromes), these human constructs may mask what is really going on in nature.

Many “typical” hummingbird flowers belong to species that produce diluted nectar with lower sugar concentrations. Yet the hummingbird’s signature hovering flight burns massive amounts of calories. From the hummingbird’s perspective, it would therefore be much more efficient to drink from flowers with more concentrated nectars. Hummingbirds are also known to have acute color vision and show no innate preference for the color red—in other words, there is no reason for them to exclusively focus on red or orange flowers. And their long and slender bills are perfectly capable of extracting nectar from both long and shallow flowers. Finally, hummingbirds do have a sense of smell. So why would hummingbirds go out of their way to visit a limited selection of reddish, long-tubed, scentless flowers that produce cheaper nectar when they could feed from more suitable nearby sources in a diverse buffet of flowers?

Flowers that are “atypical,” or lacking the characteristics we associate with hummingbird-visited flowers (note that they vary in color, shape, odor, and nectar concentration):

Nuttall’s larkspur (delphinium nuttallianum)

Nuttall’s larkspur
Delphinium nuttallianum

Glacier lily (Erythronium grandiflorum)

Glacier lily
Erythronium grandiflorum

Ballhead waterleaf (Hydrophyllum capitatum)

Ballhead waterleaf
Hydrophyllum capitatum

The Garden’s  Paul CaraDonna, Ph.D., and his research collaborators Nickolas Waser, Ph.D., and Mary Price, Ph.D., of the Rocky Mountain Biological Laboratory, discovered that it all comes down to the basic economics that maximize energetic gain at minimal energetic cost. While camping and conducting research across the American Southwest, the three researchers kept observing something curious and unexpected: hummingbirds routinely visited flowers that lacked the expected typical characteristics of hummingbird flowers.

To make sense of these observations, the team dug back into their field notes from the past four decades and began to look more closely at the potential profitability of atypical vs. typical flowers for hummingbirds. Their field notes contained information on hummingbirds’ foraging rates at flowers and measurements of the nectar sugar concentrations; with this information, the team was able to calculate the energetic profits that could be gained by a hummingbird foraging at either type of flower.

How do hummingbirds choose flowers?

A broad-tailed hummingbird (Selasphorus platycercus) feeding from the so-called “atypical” flowers of pinedrops (Pterospora andromedea). Photo courtesy: Audrey Boag

What the team found was that typical and atypical flowers overlapped considerably in their energy content and profitability for hummingbirds. In other words, most typical flowers were no better than most atypical flowers and most atypical ones were no worse than most typical ones. Taken together, this research reveals that hummingbirds are making an energetic profit—not a mistake—when visiting these atypical flowers. In fact, atypical flowers may play a critical yet underappreciated role in supporting hummingbird migration, nesting, and populations in areas that seem to be lacking in suitable floral resources. The results of this research were recently published in the peer-reviewed scientific journal The American Naturalist. Neither typical nor atypical flowers are categorically better or worse than the other, and instead show considerable overlap in the energetic gain they offer to foraging hummingbirds.

Many hummingbird conservation efforts focus solely on typical flowers. Perhaps you have come across suggested hummingbird plant lists that are dominated by typical species. Now knowing that atypical plants can support the migration and residence of hummingbirds, we can consider more than just the typical plants as food resources in habitats and along migration routes.


Karen Wang

Guest blogger Karen Wang graduated with a B.S in ecology and evolutionary biology and a B.A in creative writing from the University of Arizona in 2017. She has worked as a research assistant on a variety of projects, mostly involving pollinators such as bees and moths. 


©2018 Chicago Botanic Garden and my.chicagobotanic.org

When spring unfurls, the trillium are among the stars of the native wildflowers—and in coming years, the show at the Chicago Botanic Garden will be even more spectacular.

A ground-level view of forest trilliums in spring bloom

A ground-level view of forest trilliums in spring bloom

White trillium (Trillium grandiflorum)

White trillium (Trillium grandiflorum)

Little sweet Betsy (Trillium cuneatum)

Little sweet Betsy (Trillium cuneatum)

Yellow wakerobin (Trillium luteum)

Yellow wakerobin (Trillium luteum)

The Chicago Botanic Garden is collaborating with the Huntsville Botanical Garden in Alabama on a Trillium conservation program for the beloved woodland flower. The Huntsville Botanical Garden has one of the most complete collections of Trillium in the United States. In April, Andrew Bunting, assistant director of the Chicago Botanic Garden and director of plant collections, will pick up carefully selected rhizomes, or underground horizontal stems, from Huntsville’s collection.

Biota of North America Program (BONAP) map of Trillium in the United States

Biota of North America Program (BONAP) map of Trillium in the United States

When he returns, the rhizomes will be grown out in the nursery, and in two to three years, the Trillium plants will be replanted in areas to be determined throughout the Garden. 

Currently, the Chicago Botanic Garden has eight species of Trillium growing in the McDonald Woods, the Sensory Garden, the Native Plant Garden, and Lakeside Garden. If all goes well, the Huntsville transplants will bring dozens of more taxa, or individual types of plants, to the Garden. 

When we began our collaboration with Huntsville, we catalogued each of its Trillium species to evaluate which ones from its collection might grow in our limestone-based soils and USDA Zone 5 growing conditions. Typically, the species likes the rich, acid soils and deep shade of the ancient eastern forests. But there are several species that thrive in the more alkaline soils across the Midwest. Our goal is to expand the range of growing areas for some species and increase the overall diversity.   

Trillium plant parts illustration.

Trillium plant parts illustration from Trillium, by Fredrick W. Case and Roberta Case, Timber Press, Portland, Oregon, 1997.

Urban growth and development over the years has cleared the forests in many of the natural habitats of the species. Some species, like Trillium persistens, are extremely rare and considered endangered. Trillium are so beloved that they have appeared on two U.S. Postal Service stamps.

Come for an early spring walk to look for trillium and other wildflowers in the McDonald Woods. Or join a free guided McDonald Woods wildflower walk at 1 p.m. on Saturday, April 21, as part of the Garden’s new Unearth Science festival.


Marcia Glenn

Marcia Glenn volunteers with Andrew Bunting and the Plant Collections team, and Lisa Hilgenberg in the Regenstein Fruit & Vegetable Garden. She has more than 30 years of experience in agriculture, international trade, government policy, and management, and has served on several boards. She has a bachelor’s degree and master’s degree in agricultural economics and is a master gardener.


Photos by Huntsville Botanical Garden
©2018 Chicago Botanic Garden and my.chicagobotanic.org

Bim Willow, who has taught classes in willow work at the Chicago Botanic Garden for more than a decade, never tires of showing students how to tap into their creativity.

“That twinkle in the eyes of the students after they finish a project and look at it and they’re dancing, they’re giggling, and they say ‘I can’t believe I made it.’ Then they come back the next year and say, ‘You know, I’ve showed off my piece to people and everybody who has seen my piece says: I can’t believe you made that! But now I do believe it.’

That realization, says Willow, about going from ‘I can’t believe I can do this’ to ‘I now believe I can,’ is a big reason he’ll teach four Willow Workshops—Holiday Tree, Garden Bench, Rustic Reindeer, and Rocking Chair—November 11 at the Garden.

A chair workshop participant begins to attach the bent willow forming the seat and back to her chair frame.

A chair workshop participant begins to attach the bent willow forming the seat and back to her chair frame.

A happy Bim WIllow student works on her rustic shelf from an earlier workshop.

A happy Bim WIllow student works on her rustic shelf from an earlier workshop.

Students, he says, need not be masters of hammers and nails. “It’s really easy to learn how to nail, but it’s a lot harder to unlearn how to do it the wrong way—like so many other things in life.”

And while he teaches techniques, Willow also encourages individual creativity. “Students learn the technique of how to make something structurally sound,” he told us in a phone chat. “That’s functional. But the aesthetic part is now in their ballpark.”

“That’s where you get to use your imagination and take these sticks and create something beautiful out of it,” he says. “Imagination is all in our head. And my class is about taking it out and playing with it.”

Bim Willow supervises construction on a rustic chair frame.

Bim Willow supervises construction of a rustic chair frame.

Bim’s fascination with willow prompted a name tweak for this artist born Lawrence Schackow 65 years ago. Willow, who lives in southwestern Michigan, built his first willow chair in 1972 and started Willow Works, Inc., in 1985.

“Willow is one of those renewable resources. And for the style of furniture I build, willow is the best wood because of its flexible nature. But mostly because it’s free.

“For for the benches, we’re mostly going to be using sassafras, which is free wood. It’s durable,” he says. “And willow will be just for the trimming. I use willow that grows in the ditches that people are trying to get rid of because it clogs up the ditches. It’s not like a weeping willow tree.  …The willow that I use is a resource that people are trying to get rid of.”

“Basically, the class is about taking anything that people are trying to get rid of and turning it into something that people want.”

Willow calls himself “an author, artist, poet, and fool” on his Facebook page—a nod to his early work as a mime and clown. But he has several books to his credit, including furniture-making books, children’s books, and more in the works, like a collection of his one-liners he calls Bimisms.

“We are taught at an early age to stop being creative and start becoming productive,” he says. “And I’m here to reverse that.”

It’s about taking people back to a time when creativity was something they did instead of bought. And each one of us has that creative side.

If you think about a machine, he said, “I’m more of a social lubricant than a cog or a gear. So I slide in and out of the machine with creativity and show people that (creativity) can help take some of the friction out. But it’s also about people finding that within themselves.”


Guest blogger Judith Hevrdejs-King is a freelance writer.


©2017 Chicago Botanic Garden and my.chicagobotanic.org

Gerit Quealy is passionate about the Bard of Avon.

Her latest book, Botanical Shakespeare: An Illustrated Compendium of All the Flowers, Fruits, Herbs, Trees, Seeds, and Grasses Cited by the World’s Greatest Playwright (HarperCollins), is beautiful proof. She will talk Shakespeare at a lecture and book signing at 1 p.m. Sunday, October 15, at the Chicago Botanic Garden.

Honeysuckle illustration by Sumié Hasegawa-Collins for Botanical Shakespeare: An Illustrated Compendium

Honeysuckle illustration by Sumié Hasegawa-Collins

The book’s splendid illustrations are by Sumié Hasegawa-Collins and its foreword is by Helen Mirren—yes, Dame Helen’s an avid gardener. But it is Quealy, the book’s writer and editor, who dug through historical manuscripts from the sixteenth century’s “Elizabethan horticultural boom” to unearth more than 170 plant references in Shakespeare’s poems and plays.

For instance, apples often play a role in the Bard’s works, for as Quealy writes: “Shakespeare finds the apple ripe for metaphor.” Consider the Apple-John variety in Henry IV: “I am withered like an old Apple-John,” says Falstaff.

The mix of history and mystery captivated Quealy, who as a child read every Nancy Drew book she could find. It took 20 years to research and compile the book. “Letters and manuscripts still have not been transcribed because not enough people know how to do it, and it’s costly and time-consuming,” she told us. “And I was like, wow, there’s this secret repository of stuff.”

With no historical photographs to work with, though, Quealy and artist Sumie “had a lot of talks about the color things were.”

Gourd illustration by Sumié Hasegawa-Collins for Botanical Shakespeare: An Illustrated Compendium

Gourd by Sumié Hasegawa-Collins

The book should charm gardeners who might prepare an autumn feast by emulating the Bard’s locavore and organic credentials. Quealy suggests featuring carrots, turnips, potatoes, leeks, apples, grapes, plums, pears, thyme, or marjoram. Shakespeare, as noted in Quealy’s book, can provide conversation starters for each of these ingredients.

Potatoes: “Let the sky rain potatoes; let it thunder to the tune of Greensleeves…” (Falstaff in Merry Wives of Windsor)

Apples:  “I will make an end of my dinner. There’s Pippins and cheese to come.” (Sir Hugh Evans in Merry Wives of Windsor)

Grapes:  “The tartness of his face sours ripe grapes.” (Menenius in Coriolanus)

Leeks: “His eyes were green as leeks.” (Thisbe in A Midsummer Night’s Dream)

Plums: “There’s no more faith in thee than in a stewed prune.” (Falstaff in Henry IV)

Quealy has been in love with the Bard since a traveling troupe performed Twelfth Night for her third-grade class. “I just think the story and the way the story unfolded, maybe the rhythm of the language, is something that I responded to,” she says.

Grapes illustration by Sumié Hasegawa-Collins for Botanical Shakespeare: An Illustrated Compendium

Grapes illustration by Sumié Hasegawa-Collins

Born in Virginia, raised in Florida, and now living in New York, Quealy has been an actor (theater, television), a journalist (newspapers, magazines), and an author. A television project is in the works (FLOTUS: Playing the Woman Card in the White House); as is a project on Shakespeare’s kitchen.

The Garden event will include a lutenist and a soprano, who will perform during the free October 15 program (preregistration required). Quealy hopes the event and the book will help people connect with Shakespeare. “Shakespeare is all around you.”


Guest blogger Judith Hevrdejs-King is a freelance writer.


©2017 Chicago Botanic Garden and my.chicagobotanic.org

The Supreme Court has been asked to opine on many critical issues of its time. These cases have had profound impacts on our society and even the progression of democracy. But perhaps the most important Supreme Court case of all time—at least if you are a hard-core plant geek—was Nix v. Hedden, 1893, in which the Court ruled that the tomato is, for the purposes of taxation, a vegetable.

In the spring of 1886, the Nix family made their living importing tomatoes into New York City from the West Indies. Based on the Tariff Act of 1883, the New York Port tax collector assessed a duty on these imported tomatoes. The Tariff Act required a 10 percent duty on “vegetables in their natural state…” But, the Nix family contended, a tomato is a fruit, botanically speaking, and should not be taxed as a vegetable. The New York tax collector was unmoved by this argument and forced the family to pay the tax, though he did record that the tax was paid under protest.

Blindfolded Lady Justice weighs a tomatoPeople were just as reluctant to pay taxes in 1886 as they are today, and as any good botanist of the nineteenth or twenty-first centuries would tell you, the tomato is indeed a fruit. Its tissues derive from the reproductive organs of the plant (and contain seeds), making it a textbook fruit. It’s not even botanically confusing like the oddball strawberry, which is technically a swollen receptacle that holds fruits (the little black achenes on the strawberry’s surface). A tomato is about as clearly a fruit as there is, botanically speaking.

Yet, in common language, we tend to think of fruits as sweet and vegetables as savory. Or perhaps more basically, fruits are for dessert and vegetable go with the main course.

When the tax assessor for the New York Harbor used the common language meaning of tomato as the rationale to levy a tax, in opposition to the botanical definition used by the Nix family, I doubt he knew he was opening a legal can of worms that would end up in the Supreme Court.

The Nix family sued the tax collector. The case was heard by the Circuit Court of the Southern District of New York. The case primarily consisted of entering into testimony the dictionary definitions of fruit and vegetable. The court sided with the tax collector, and the Nixes appealed. Somewhat amazingly, the Supreme Court agreed to hear the case, and registered judgement on May 10, 1893.

By this point, the case was not so much about whether or not a tomato is botanically a fruit. In fact, in his opinion, Justice Horace Gray of Massachusetts freely admitted that “botanically speaking, tomatoes are the fruit of the vine…” But he made a distinction between the common language of the people and the botanical definition. Specifically, he noted that tomatoes are “usually served at dinner in, with, or after the soup, fish, or meats which constitute the principle part of the repast, and not, like fruits generally, as dessert.” He even cited from Supreme Court precedent. In 1889, Robertson v. Salomon, the Court held that, again for tax purposes, white beans (which definitely are seeds) should be taxed as vegetables, and not classified as seeds, which were exempted from taxation. Justice Joseph P. Bradley of New Jersey wrote of white beans, “We do not see why they should be classified as seeds, any more than walnuts should be so classified. Both are seeds, in the language of botany or natural history, but not in commerce nor in common parlance.”

Grape tomatoesRead more about cultivating tomatoes in our Tomato Talk series on Facebook (#CBGTomatoTalk) and at chicagobotanic.org

The Supreme Court unequivocally stated in Robertson v. Salomon and then reaffirmed in Nix v. Hedden that a technical definition should not necessarily stand in the way of an ordinary or common meaning. According to the high court, tomatoes and white beans are not fruit and seeds, respectively. They can, and should, be taxed as vegetables.

These cases are important to legal history in delineating the differences between technical and common usages of words under legal dispute. But what should a botanist learn from this legal tomato obscurity?

Principally, science and the law are quite different systems. You may conflate them at your own peril. Scientific logic is not always compatible or supported by legal doctrine. Under the law, up can be down, black can be white, and tomatoes aren’t fruits.

And above all, it’s very hard to avoid paying taxes.


Dr. Ari Novy

Dr. Ari Novy

Guest blogger Ari Novy, Ph.D., is chief scientist at the Leichtag Foundation in Encinitas, California, and a research collaborator at the National Museum of Natural History in Washington, D.C. He’s interested in pretty much everything about plants, including obscure legal minutiae.


©2017 Chicago Botanic Garden and my.chicagobotanic.org