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.


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

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.


©2018 Chicago Botanic Garden and my.chicagobotanic.org

Are We There Yet? Celebrating the National Parks Service Centennial

The National Parks provide dream vacations for us nature lovers, but did you know they also serve as vital locations for forward-thinking conservation research by Chicago Botanic Garden scientists?

From sand to sea, the parks are a celebration of America’s diversity of plants, animals, and fungi, according to the Garden’s Chief Scientist Greg Mueller, Ph.D., who has worked in several parks throughout his career.

“National Parks were usually selected because they are areas of important biodiversity,” Dr. Mueller explained, “and they’ve been appropriately managed and looked after for up to 100 years. Often times they are the best place to do our work.”

As we celebrate this centennial year, he and his colleagues share recent and favorite work experiences with the parks.

PHOTO: Dr. Greg Mueller in the field.
Dr. Greg Mueller working at Big Thicket National Preserve, Texas, in 2007.

Take a glimpse into the wilderness from their eyes.

This summer, Mueller made a routine visit to Indiana Dunes National Lakeshore to examine the impact of pollution and other human-caused disturbances on the sensitive mushroom species and communities associated with trees. “One of the foci of our whole research program (at the Garden) is looking at that juxtaposition of humans and nature and how that can coexist. The Dunes National Lakeshore is just a great place to do that,” he explained, as it is unusually close to roads and industry.

Evelyn Williams, Ph.D., adjunct conservation scientist, relied on her fieldwork in Guadalupe Mountains National Park to study one of only two known populations of Lepidospartum burgessii, a rare gypsophile shrub, during a postdoctoral research appointment at the Garden. “We were able to work with park staff to study the species and make recommendations for management,” she said.

PHOTO: Dr. Evelyn Williams in Guadalupe Mountains National Park during 2014 field work.
Dr. Evelyn Williams in Guadalupe Mountains National Park during 2014 field work. Photo by Adrienne Basey.

As a Conservation Land Management intern, Coleman Minney surveyed for the federally endangered Ptilimnium nodosum at the Chesapeake and Ohio Canal National Historical Park earlier this year. “The continued monitoring of this plant is important because its habitat is very susceptible to invasion from non-native plants,” explained Minney, who found the first natural population of the species on the main stem of the Potomac River in 20 years.

PHOTO: Harperella (Ptilimnium nodosum).
Harperella (Ptilimnium nodosum) grows on scour bars of rivers and streams. Photo by Coleman Minney.

According to conservation scientist Andrea Kramer, Ph.D., “In many cases, National Parks provide the best and most intact examples of native plant communities in the country, and by studying them we can learn more about how to restore damaged or destroyed plant communities to support the people and wildlife that depend upon them.”

The parks have been a critical site for her work throughout her career. Initially, “I relied on the parks as sites for fieldwork on how wildflowers adapt to their local environment.”

Today, she is evaluating the results of restoration at sites in the Colorado Plateau by looking at data provided by collaborators. Her data covers areas that include Grand Canyon National Park, Capitol Reef National Park, and Canyon de Chelly National Monument.

Along with colleague Nora Talkington, a recent master’s degree graduate from the Garden’s program in plant biology and conservation who is now a botanist for the Navajo Nation, Dr. Kramer expects the results will inform future restoration work.

PHOTO: Dr. Andrea Kramer at Arches National Park.
Dr. Kramer collects material from Arches National Park as a part of her dissertation research in 2003.

At Wrangell–St. Elias National Park and Preserve in Alaska, Natalie Balkam, a Conservation Land Management intern, has been hard at work collecting data on vegetation in the park and learning more about the intersection of people, science, and nature. “My time with the National Park Service has exposed me to the vastly interesting and complex mechanics of preserving and protecting a natural space,” she said. “And I get to work in one of the most beautiful places in the world—Alaska!”

PHOTO: The view from survey work in Elodea, part of the Wrangell–St. Elias National Park Preserve in Alaska.
The view from survey work in Elodea, part of the Wrangell–St. Elias National Park Preserve in Alaska. Photo courtesy National Park Service.

The benefits of conducting research with the National Parks extend beyond the ability to gather high-quality information, said Mueller. Parks retain records of research underway by others and facilitate collaborations between scientists. They may also provide previous research records to enhance a specific project. Their connections to research are tight. But nothing is as important as their ability to connect people with nature, said Mueller. “That need for experiencing nature, experiencing wilderness is something that’s critical for humankind.”

For research and recreation, we look forward to the next 100 years.


©2016 Chicago Botanic Garden and my.chicagobotanic.org

A 20-Year Legacy of Conservation Conversations

For more than two decades, leaders in conservation science have come to the Chicago Botanic Garden each summer to discuss timely topics from monarch butterflies to assisted plant migration.

Butterfly on Liatris
Butterfly on Liatris

Seeds will be planted again on Monday, June 13, when regional stewardship professionals, academics, restoration volunteers, and interns gather for the Janet Meakin Poor Research Symposium. The annual day of lectures and discussions covers the latest findings in conservation research and best practices in restoration, while inspiring conversations and new partnerships.

“I think the science that pertains to land management is always evolving, and therefore best practices are always evolving,” said Kay Havens, Ph.D., Medard and Elizabeth Welch senior director, Ecology and Conservation, and the moderator of the symposium.

The 2015 symposium focused on restoration solutions for large-scale implementation, and this year’s theme, Seed Sourcing for Restoration in a Changing Climate, builds on the concept of seed management. “It focuses on conservation research and restoration and tries to make links with the land management community—so not just reporting the science but also reporting how that could influence land management,” explained Dr. Havens. This subject is especially timely, according to Havens, as it follows the first year of the National Seed Strategy for Rehabilitation and Restoration. The Garden has played a key role in establishing the seed strategy, which will create a network to ensure native seeds are available in restoration efforts, especially in fire-ravaged western rangelands.

The Dixon Prairie in July
The Dixon Prairie in July

“I think the need for restoration increases annually,” said Havens. “We are facing a more and more degraded planet every year, and as the climate changes and natural disasters like hurricanes and floods increase, the need for restoration increases.”

Read more about the symposium or register online for Seed Sourcing for Restoration in a Changing Climate today.


©2016 Chicago Botanic Garden and my.chicagobotanic.org

Save the Earth, Watch Dandelions Grow

I am often asked, “What can kids do to help the Earth?”

There is a standard litany of “Reduce, Reuse, Recycle” suggestions that almost everyone can tell you: recycle your garbage, turn the lights off when you leave a room, turn the water off while brushing your teeth, and so forth. 

EarthWe’ve been saying these same things for decades. And while they’re great ideas, they’re things we should all be doing. It’s time to give kids a chance to do something bigger. During Climate Week this year, I am offering a different suggestion: Watch dandelions grow and participate in Project BudBurst.

PHOTO: Dandelions.
These happy dandelions could contribute valuable information to the science of climate change.

Project BudBurst is a citizen science program in which ordinary people (including kids 10 years old and up) contribute information about plant bloom times to a national database online. The extensive list of plants that kids can watch includes the common dandelion, which any 10-year-old can find and watch over time.

Why is this an important action project?

Scientists are monitoring plants as a way to detect and measure changes in the climate. Recording bloom times of dandelions and other plants over time across the country enables them to compare how plants are growing in different places at different times and in different years. These scientists can’t be everywhere watching every plant all the time, so your observations may be critical in helping them understand the effects of climate change on plants.

What to Do:

1. Open the Project Budburst website at budburst.org and register as a member. It’s free and easy. Click around the website and read the information that interests you.

2. Go to the “Observing Plants” tab and print a Wildflower Regular Report form. Use this form to gather and record information about your dandelion. 

3. Find a dandelion in your neighborhood, preferably one growing in a protected area, not likely to be mowed down or treated with weed killers, because you will want to watch this plant all year. It’s also best if you can learn to recognize it without any flowers, and that you start with a plant that has not bloomed yet.

4. Fill in the Wildflower Regular Report with information about the dandelion and its habitat.

Common Plant Name: Common dandelion

Scientific Name: Taraxacum officinale

Site Name: Give the area a name like “Green Family Backyard” or “Smart Elementary School Playground”

Latitude and Longitude: Use a GPS device to find the exact location of your dandelion. (Smartphones have free apps that can do this. Ask an adult for help if you need it.) Record the letters, numbers, and symbols exactly as shown on the GPS device. This is important because it will enable the website database to put your plant on a national map.

Answer the questions about the area around your plant. If you don’t understand a question, ask an adult to help you.

PHOTO: This is a printout from the Project BudBurst Website, that asks about the location of the plant and provides places to record bloom times, as well as other comments.
The BudBurst Wildflower Regular Report is easy to use and will guide you through the process.
girl with data sheet
After you find a dandelion you want to watch, record information about the location of the plant.

5. Now you’re ready to watch your dandelion. Visit it every day that you can. On the right side of the form, record information as you observe it.

budburst notebook

  • In the “First Flower” box, write the date you see the very first, fully open yellow flower on your dandelion.
  • As the plant grows more flowers, record the date when it has three or more fully open flowers.
  • Where it says “First Ripe Fruit,” it means the first time a fluffy, white ball of seeds is open. Resist the temptation to pick it and blow it. Remember, you are doing science for the planet now!
  • For “Full Fruiting” record the date when there are three seedheads on this plant. It’s all right if the seeds have blown away. It may have new flowers at the same time.
  • In the space at the bottom, you can write comments about things you notice. For example, you may see an insect on the flower, or notice how many days the puffball of seeds lasts. This is optional.
  • Keep watching, and record the date that the plant looks like it is all finished for the year—no more flowers or puffballs, and the leaves look dead.
  • When your plant has completed its life cycle, or it is covered in snow, log onto the BudBurst website and follow directions to add your information to the database.


Other Plants to Watch

You don’t have to watch dandelions. You can watch any of the other plants on the list, such as sunflower (Helianthus annuus) or Virginia bluebell (Mertensia virginica). You can also watch a tree or grass—but you will need to use a different form to record the information. Apple (Malus pumila), red maple (Acer rubrum), and eastern white pine (Pinus strobus) trees are easy to identify and interesting to watch. If you are an over-achiever, you can observe the butterfly milkweed (Asclepias tuberosa) bloom times and do citizen science research for monarchs at the same time! (The USDA Forest Service website provides information about that; click here for more information.) 

PHOTO: Two girls are looking closely at a milkweed plant that has about eight green seed pods.
These students are observing a milkweed that is in the “First Ripe Fruit” stage.

For the past two springs, educators at the Chicago Botanic Garden have taught the fifth graders at Highcrest Middle School in nearby Wilmette how to do Project BudBurst in their school’s Prairie Garden. The students are now watching spiderwort, red columbine, yellow coneflower, and other native plants grow at their school. Some of these prairie plants may be more difficult to identify, but they provide even more valuable information about climate.

So while you are spending less time in the shower and you’re riding your bike instead of asking mom for a ride to your friend’s house, go watch some plants and help save the planet even more!


©2015 Chicago Botanic Garden and my.chicagobotanic.org