plant science – My Chicago Botanic Garden

The surprising science behind hummingbirds and flowers

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.

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.

Wanted: Leaf Peepers for Science

Have you ever noticed the first crocuses poking out of the snow or the brilliant, changing colors of fall leaves? If so, we need your help with the critical work of studying how plants are affected by a changing climate.

Budburst, a project adopted by the Chicago Botanic Garden in 2017, brings together citizens, research scientists, educators, and horticulturists to study “phenology,” or the life-cycle events of plants. Wildflower phenology events, for example, are fairly simple: first flower, full flower, first fruit, and full fruiting. Deciduous trees, on the other hand, are more complex, with stages from first buds to leaf drop.

Sweetgum in the summer - Budburst — Sweetgum *(Liquidambar styraciflua)* seed in the summer.

Sweetgum in the fall - Budburst — Sweetgum *(Liquidambar styraciflua)* leaves in the fall.

Budburst builds on the basic human drive to notice this kind of changing nature around us and record the information to a database for scientists to review. As director of Budburst, I’m excited to hear about your observations on Fall into Phenology, a study on the autumnal changes you see in plants, or the Nativars Research Project, which looks at how bees, butterflies, and other pollinators react to cultivated varieties of native plants.

Budburst’s Fall into Phenology is not limited to just leaf color and seed; it is about observing plants in the fall. This will be my second autumn with Budburst and the Garden, and I’m looking forward to watching some my favorite plants go through their life-cycle changes. I’ll be keeping an eye on the sweetgum trees (Liquidambar styraciflua) underneath my window at the Regenstein Learning Campus, for instance. I can’t wait to see the beautiful shades of yellow or orange or…well, you just never know.

Spotlighting Women in Science at the Garden

The number of women in science is pretty dismal. Despite earning about half the doctorates in science, only 21 percent of full science professors in the United States are women,* but I feel very fortunate to work at an institution committed to inclusiveness and diversity. At the Chicago Botanic Garden, 25 of our 47 scientific staff are women; our graduate student body is 61 percent female.

Still, implicit gender biases persist in science, resulting in fewer women in top positions, along with women earning less pay, winning fewer grants, and publishing fewer papers. This comes at a time when we are faced with numerous grand challenges in science and need a diversity of approaches to tackle those challenges.

In the Chicago Botanic Garden’s science program, we are conducting research on how human activities are affecting plants through climate change, habitat fragmentation, introduction of invasive species, pollinator loss, pollution, and more. These threats to plants are unlikely to diminish in the foreseeable future, and we are finding ways to conserve plants in changing and challenging environments. We are working hard to protect the plants and plant communities upon which we all depend. We are also working hard to create a pipeline into science for all—especially traditionally under-represented groups—through our Science Career Continuum, because diversity of plants and diversity of scientists are both good things.

Meet some of our women scientists:

Lauren Umek studies how invasive species change plant communities and soil properties in the Chicago region and how this can improve restoration methods.

Nyree Zerega studies evolution/genomics in underutilized tropical fruit trees and their wild relatives to promote and conserve food diversity.

Botanist, seed conservationist and geographer Emily Yates has conserved thousands of seeds to protect the native tallgrass prairie ecosystem of the American Midwest. — Botanist, seed conservationist, and geographer Emily Yates has conserved thousands of seeds to protect the native tallgrass prairie ecosystem of the Midwest.

Ph.D. student Colby Witherup uses computers to study plant DNA, looking for signs of evolution in genes that control sexual reproduction. — Ph.D. candidate Colby Witherup studies plant DNA, looking for signs of evolution in genes that control sexual reproduction.

Evelyn Williams Ph.D. (left, with Adrienne Basey) traveled to Guadalupe Nation Park in Texas to study the shrub Burgess' Scalebroom. — Evelyn Williams, Ph.D., (left, with Adrienne Basey) traveled to Guadalupe Nation Park in Texas to study the shrub Burgess’ scalebroom.

Amy Waananen studies populations of Echinacea angustifolia in Western Minnesota as a research assistant for The Echinacea Project, a long-term ecological study that began in 1995. — Amy Waananen studies populations of purple coneflower (*Echinacea angustifolia)* in western Minnesota as a research assistant for The Echinacea Project, a long-term ecological study that began in 1995.

Mary Patterson studies restoration, invasive species, and fire ecology with a focus in the Western United States.

Joan O'Shaughnessy manages the Dixon Prairie at the Garden. — Joan O’Shaughnessy manages the Dixon Prairie at the Garden.

Kelly Ksiazek-Mikenas studies how green roofs can provide habitat for native plant species.

Andrea Kramer, Ph.D., conducts research on native plants to support ecological restoration that sustains people, wildlife, and the planet.

Rachel Goad is a botanist with a background in restoration ecology and a keen interest in native plant conservation. — Rachel Goad (far right) is a botanist with a background in restoration ecology and a keen interest in native plant conservation.

Louise Egerton-Warburton's work examines soil fungal diversity and functioning and its role in ecosystem processes. — Louise Egerton-Warburton, Ph.D., does work examining soil fungal diversity and functioning and its role in ecosystem processes.

Research assistant Susan Deans uses neutral genetic markers to examine how well gardens and conservation collections capture the remaining wild genetic diversity of threatened Hawaiian plant species.

Ph. D. student Becky Barak studies plant diversity in restored tallgrass prairies. — Ph.D. candidate Becky Barak studies plant diversity in restored tallgrass prairies.

Kay Havens studies rare plant conservation, restoration, pollination and plant responses to climate change. — Kay Havens, Ph.D., studies rare plant conservation, restoration, pollination and plant responses to climate change.

*From Inequality quantified: Mind the gender gap, by Helen Shan, 06 March 2013, nature.com

60-Second Science: Prairies Need Fire

Becky Barak is a Ph.D. candidate in Plant Biology and Conservation at the Chicago Botanic Garden and Northwestern University. She studies plant biodiversity in restored prairies, and tweets about ecology, prairies, and her favorite plants at @BeckSamBar.

A dark, stinky plume of smoke rising from a nature preserve might be alarming. But fire is what makes a prairie a prairie.

A prairie is a type of natural habitat, like a forest, but forests are dominated by trees, and prairies by grasses. If you’re used to the neatly trimmed grass of a soccer field, you may not even recognize the grasses of the prairie. They can get so tall a person can get lost.

Prairies are maintained by fire; without it, they would turn into forests. Any chunky acorn or winged maple seed dropping into a prairie could grow into a giant tree, but they generally don’t because prairies are burned every few years. In fact, fossilized pollen and charcoal remains from ancient sediments show that fire, started by lightning and/or people, has maintained the prairies of Illinois for at least 10,000 years. Today, restoration managers (with back up from the local fire department), are the ones protecting the prairie by setting it aflame.

PHOTO: Chicago Botanic Garden ecologist Joah O'Shaughnessy monitors a prairie burn. — Garden ecologist Joan O’Shaughnessy monitors a spring burn of the Dixon Prairie.

PHOTO: New growth after a prairie burn. — New growth emerges a scant month after the prairie burn.

Prairie plants survive these periodic fires because they have incredibly deep roots. These roots send up new shoots after fire chars the old ones. Burning also promotes seed germination of some tough-seeded species, and helps keep weeds at bay by giving all plants a fresh start.

Read more about our conservation and restoration projects on the Chicago Botanic Garden website. Want to get involved in our local ecosystem conservation? Find your opportunity with Chicago Wilderness.

Students in the Chicago Botanic Garden and Northwestern University Program in Plant Biology and Conservation were given a challenge: Write a short, clear explanation of a scientific concept that can be easily understood by non-scientists. This is our third installment of their exploration.

60-Second Science: Plants’ Roots Helped Them Move to Land

Alicia Foxx is a second-year Ph.D., student in the joint program in Plant Biology and Conservation between Northwestern University and the Chicago Botanic Garden. Her research focuses on restoration of native plants in the Colorado Plateau, where invasive plants are present. Specifically, she studies how we can understand the root traits of these native plants, how those traits impact competition, and whether plant neighbors can remain together in the plant community at hand.

Life for plants on land is hard because the environment can become dry. Water is important because it is used when plants take in sunlight and carbon dioxide to make energy; this is called photosynthesis. In fact, the largest object in a plant cell is a sack that holds water. Without water, plants would die.

Plants first evolved in water, which is a comfortable place: there is little friction, you almost feel weightless, and…there was plenty of water back then. These plants had no difficulty photosynthesizing, as water diffused quite easily into their leaf cells! They had little use for roots.

Evolving Plant Structures

In the time plants evolved to live on land (100 million years later), water shortages and the need to be anchored in place became issues and restricted plants to living near bodies of water. Some plants evolved root-like structures that were mostly for anchoring a plant in place, but also took in some water.

It wasn’t until an additional 50 million years after the move on to land that true roots evolved, and these are very effective at getting the resources essential for photosynthesis and survival. In fact, the evolution of true roots 400 million years ago is associated with the worldwide reductions in carbon dioxide, since more resources could be gathered by roots for photosynthesis. Importantly, plants were no longer tied to bodies of water!

PHOTO: tree roots. — Large roots anchor a plant in place.

PHOTO: bulb with tiny bulblets and root hairs. — Tiny root hairs on a bulb take up nutrients when moisture is present.

Water issues continued, however, even with true roots. Early roots were very thick and could not efficiently search through the soil for resources. So plants either evolved thinner roots, or formed beneficial associations with very tiny fungi (called mycorrhizal fungi) that live in the soil. These fungi create very thin, root-like structures that allow for more effective resource uptake. In general, while life on land is hard, plants have evolved ways to cope via their roots.

Garden scientists are studying the relationships between plants and mycorrhizal fungi in the soil. Orchids are masters of nutrient collection. The vanilla orchid has terrestrial (in soil) and epiphytic (above ground, or air) roots—and forms relationships with fungi for nutrient collection. Read more about research on Vanilla planifolia here.