“I am interested in understanding and predicting how microbial communities influence interactions between plants and insects,” she says. The Vannette lab “uses tools and concepts from microbial ecology, chemical ecology, and community ecology to better understand the ecology and evolution of interactions among plants, microbes and insects."
Now the UC Davis assistant professor has two more opportunities that will enable her to pursue her research: she recently received two National Science Federation (NSF) grants.
One is a five-year Faculty Early Career Development (CAREER) Program award, titled “Nectar Chemistry and Ecological and Evolutionary Tradeoffs in Plant Adaptation to Microbes and Pollinators.” NSF grants CAREER awards to early career faculty “who have the potential to serve as academic role models in research and education and to lead advances in the mission of their department or organization,” a NSF spokesman said.
The other is a three-year collaborative grant, “The Brood Cell Microbiome of Solitary Bees: Origin, Diversity, Function, and Vulnerability.”
Vannette serves as a co-principal investigator with professor Bryan Danforth, Cornell University; research entomologist Shawn Steffan of the USDA's Agricultural and Research Service, University of Wisconsin; and assistant professor Quinn McFrederick, UC Riverside.
“Plants interact with a variety of organisms. The flowers and the nectar plants produce are adapted to attract beneficial organisms like bees or hummingbirds. However, microbes like bacteria and fungi also inhabit flowers and can reduce plant reproduction. Plant traits can reduce microbial growth in nectar, but this may also reduce pollinator visitation. This project will investigate if plants that are pollinated by different organisms (e.g. birds vs bees vs flies) differ in their ability to reduce microbial growth and if nectar chemistry is associated with microbial growth. This project will examine if nectar traits can be used to breed plants to be more resistant to harmful microbes without reducing attraction to pollinators. Resistance to microbes is beneficial in agricultural contexts where floral pathogens can limit food production but crops still rely on pollination.
“This research will link variation in plant phenotype to microbial abundance and species composition, and microbial effects on plant-animal interactions,” she noted. “This project will use a tractable system: the microorganisms growing in floral nectar, which can influence floral visitors and plant reproduction. The underlying hypothesis tested is that plant traits can facilitate or reduce microbial growth, and the community context (e.g., presence of pollinators) influence ecological and evolutionary outcomes.”
Vannette will perform the research activities using 1) a community of co-flowering plant species and 2) genotypes within California fuchsia (Epilobium canum). “Experiments will characterize variation in microbial growth, nectar chemistry, and microbial effects on plant reproduction and floral visitor behavior and the interactions of these factors,” she related in her abstract. “ Experiments and analysis will reveal how variation in nectar chemistry is associated with microbial growth and species composition in nectar, and subsequent effects on plant-pollinator interactions including plant reproduction. Experiments across Epilobium genotypes will elucidate how microbes affect microevolution of floral traits in a community context.”
The project “will engage students from a large undergraduate class to participate in practitioner-motivated research projects,” she wrote. “Students from the Animal Biology major, including in the class ABI 50A will participate in outreach on pollinator-friendly plantings for horticultural and landscaping. The project will support students recruited from diverse and underrepresented backgrounds to participate in independent projects related to project objectives, including hosting students through the Evolution and Ecology Graduate Admissions Pathway (EEGAP), a UC-HCBU program." The program connects faculty and undergraduate scholars at both UC (University of California) and HBCU (Historically Black Colleges and Universities) campuses
The collaborative grant will enable the researchers to do cutting-edge research as they investigate the diverse community of bacteria and yeasts in the pollen and nectar diet of bees.
“Bees are the single most important pollinators of flowering plants worldwide,” the co-investigators wrote in their abstract. “Over 85% of the 325,000 flowering plant species on earth depend on animals for pollination, and the vast majority of pollination is carried out by bees. Annually, bees are estimated to contribute $15 billion to US crop production and $170 billion to global crop production. High-value bee-pollinated crops include apple and other early spring tree fruits, strawberries, blueberries, cherries, cranberries, squash and pumpkins, tomatoes, almonds, and many others. The economic viability of US agricultural production is dependent on stable and healthy wild and domesticated bee populations.”
“However, bee populations are threatened by a variety of factors, including habitat loss, pathogen spillover, invasive plants and animals, and pesticide use, which can disrupt the normal microbial symbionts essential for bee larval development (the ‘brood cell' microbiome),” they pointed out in their abstract. “This research project focuses on understanding what role microbes play in the larval nutrition in a wide variety of bee species. Previous research has documented a diverse community of bacteria and yeasts in the pollen and nectar diet of bees. As larvae consume these pollen/nectar provisions they are ingesting microbes, and our preliminary results indicate that these microbes form an essential component of the larval diet. This project has the potential to significantly modify how we view the 120 million-year-old partnership between bees and flowering plants, and will provide essential information for developing long-term bee conservation efforts. Project outreach efforts include educational activities on solitary bees for K-12 students and interactive demonstrations of bee-microbe-flower interactions for broad audiences.
The co-principal investigators said that the project will use cutting-edge methods to (1) document the microbial diversity in flowers and pollen provisions, (2) determine the nutritional role of microbes in larval development and health, and (3) understand how alterations in microbial community impact larval development.
To document microbial diversity in both host-plant flowers and pollen provisions, the research team will use amplicon sequencing and microbial metagenomics. These methods will document the microbial species present in pollen provisions as well as the metabolic activities these microbes perform during pollen maturation. Screening the pollen and nectar of host-plant species will provide key insights into the source of the brood cell microbiome. To determine the nutritional role of the microbial community the research team will use two methods from trophic ecology: compound specific isotope analysis and neutral lipid fatty acid analysis. These analyses will permit the research team to track the origin (floral or microbial) of amino acids and fatty acids in the larval diet of 15 focal bee species.
Finally, through manipulative laboratory experiments, the research team will determine how modifications of the microbial communities impact larval development. They hope by combining the results of these studies, the researchers will provide a comprehensive understanding of how bees and flowering plants interact via their shared microbial partners.
The collaborative project is funded jointly by the Systematics and Biodiversity Sciences Cluster (Division of Environmental Biology) and the Symbiosis, Defense and Self-recognition Program (Division of Integrative Organismal Systems).
Vannette, a Hellman Fellow, joined the UC Davis Department of Entomology and Nematology in 2015 after serving as a postdoctoral fellow at Stanford University's biology department. As a Gordon and Betty Moore Foundation Postdoctoral Fellow from 2011 to 2015, she examined the role of nectar chemistry in community assembly of yeasts and plant-pollinator interactions.
A native of Hudsonville, Mich., Vannette received her doctorate in ecology and evolutionary biology from the University of Michigan, in 2011. Her dissertation was entitled “Whose Phenotype Is It Anyway? The Complex Role of Species Interactions and Resource Availability in Determining the Expression of Plant Defense Phenotype and Community Consequences.”
Bee scientist James Nieh, a UC San Diego professor in the Section of Ecology, Behavior and Evolution, Division of Biological Sciences, will present the first fall quarter seminar hosted by UC Davis Department of Entomology and Nematology.
Nieh will speak on "Animal Information Warfare: How Sophisticated Communications May Arise from the Race to Find an Advantage in a Deadly Game Between Honey Bees and Their Predators" at 4:10 p.m., Wednesday, Sept. 25 in 122 Briggs Hall. Brian Johnson, associate professor of entomology, is the host.
"In addition to the classical arm race that has evolved between predators and prey, information races also occur, which can lead to the evolution of sophisticated animal communication," Nieh says in his abstract. "Such information can shape the food web and contribute to the evolution of remarkable communication strategies, including eavesdropping, referential signaling and communication within and between species, including between predators and prey."
"I focus on the world of information exchange (acoustic, olfactory and visual) that has co-evolved between Asian honey bees (Apis cerana, A. florea, and A. dorsata) and their predators, the Asian hornets (Vespa velutina and V. mandarinia)," Nieh says. "I will explore how and why such information races occur through the remarkable examples provided by these high social insects."
He presented a TED talk on "Bees and Us: an Ancient and Future Symbiosis" in July 2019.
A native of Taiwan, Nieh grew up in Southern California and received his bachelor's degree in organismic and evolutionary biology in 1991 from Harvard University, Cambridge, and his doctorate in neurobiology and behavior from Cornell University, Ithaca, N.Y., in 1997. He subsequently received an NSF-NATO postdoctoral fellowship to study at the University of Würzburg in German. A Harvard junior fellowship followed.
Nieh joined the faculty of the Section of Ecology, Behavior and Evolution in 1997 as an assistant professor, advancing to associate professor in 2007 and professor in 2009. He served as vice chair of the section from 2009 to 2014, and as chair from 2014 to 2017.
His latest co-authored research, published in the journal Chemosphere in 2019, is titled Combined Nutritional Stress and a New Systemic Pesticide (flupyradifurone, Sivanto®) Reduce Bee Survival, Food Consumption, Flight Success, and Thermoregulation.
Coordinated by assistant professor and community ecologist Rachel Vannette, the seminars will take place at 4:10 p.m., every Wednesday in Room 122 of Briggs Hall through Dec. 5 except on Nov. 20 (no seminar due to the Entomological Society of America meeting in St. Louis, Mo).
James Nieh, professor, Section of Ecology, Behavior and Evolution, Department of Biological Sciences, UC San Diego
Topic: "Animal Information Warfare: How Sophisticated Communication May Arise from the Race to Find an Advantage in a Deadly Game Between Honey Bees and their Predators" (See lab website)
Host: Brian Johnson, associate professor, Department of Entomology and Nematology
Nathan Schroeder, assistant professor, Department of Crop Sciences, University of Illinois, Urbana-Champaign
Topic: "Stem Cells and Neurobiology of Nematodes"
Host: Shahid Saddique, assistant professor, Department of Entomology and Nematology
John Mola, doctoral candidate, Neal Williams lab, Graduate Group in Ecology
Exit seminar: "Bumble Bee Movement Ecology and Response to Wildfire." Mola specializes in bee biology, pollinator ecology and population genetics.
Host: Neal Williams, professor, Department of Entomology and Nematology
Rebecca Irwin, professor of applied ecology, North Carolina State University, Raleigh, N.C.
Topic: "The Role of Floral Traits in Pollination and Bee Disease Transmission." She specializes in the ecology and evolution of multiple-species interactions, pollination biology, and species invasions
Host: Rachel Vannette, assistant professor, Department of Entomology and Nematology
Julián Hillyer, director of the program in career development and associate professor of biological sciences, Vanderbilt Institute for Infection, Immunology and Inflammation, Nashville, Tenn.
Topic: "Not So Heartless: Functional Integration of the Immune and Circulatory Systems of Mosquitoes"
Host: Olivia Winokur, graduate student, Chris Barker lab
Takato Imaizumi, professor, Department of Biology, University of Washington, Seattle
Topic: Circadian Timing Mechanisms in Plant-Pollinator Interaction"
Host: Joanna Chiu, associate professor and vice chair of the Department of Entomology and Nematology
Brock Harpur, assistant professor, Department of Entomology, Purdue University
Topic: "Beekeeping in the 21st Century: Can We Incorporate Genomics into Beekeeping?"
Host: Santiago Ramirez, associate professor, UC Davis Department of Evolution and Ecology, College of Biological Sciences
Don Cippollini, director of environmental sciences and professor, Department of Biological Sciences, Wright State University
Topic: "The Potential for Host Switching via Ecological Fitting in the Emerald Ash Borer-Host Plant System"
No seminar (meeting of Entomological Society of America in St. Louis, Mo.)
Jackson Audley, doctoral candidate who studied with the late Steve Seybold
Topic: "Semiochemical Interruption of Host Selection Behavior of the Invasive Walnut Twig Beetle, Pityophthorus juglandis."
More information on the fall seminars or schedule is available from Vannette at firstname.lastname@example.org.
A welcoming reception will take place from 6:30 to 8 p.m. Wednesday in the Good Life Garden at the Robert Mondavi Institute, 392 Old Davis Road.
Themed “Multidimensional Solutions to Current and Future Threats to Pollinator Health,” the event will cover a wide range of topics in pollinator research: from genomics to ecology and their application to land use and management; to breeding of managed bees; and to monitoring of global pollinator populations.
Co-chairs are pollination ecologist Neal Williams and Extension apiculturist Elina Lastro Niño of the UC Davis Department of Entomology and Nematology. The UC Davis Honey and Pollination Center, directed by Amina Harris, is coordinating the conference. Events manager Elizabeth Luu (email@example.com) serves as the conference coordinator.
Keynote speakers are Lynn Dicks, Natural Environment Research Council (NERC) Research Fellow, School of Biological Sciences, University of East Anglia, England, and Christina Grozinger, distinguished professor of entomology and director of the Center for Pollinator Research, Pennsylvania State University. Grozinger and Rufus Isaacs of Michigan State University launched the conference in 2012. They are held every third year; this year is the fourth conference.
Dicks will speak at 9 a.m., Thursday, July 18 on "The Importance of People in Pollinator Conservation" while Grozinger will address the crowd at 9 a.m., Friday, July 19 on "Bee Nutritional Ecology: From Genes to Landscapes."
Dicks, an internationally respected scientist, studies bee ecology and conservation. She received the 2017 John Spedan Lewis Medal for contributions to insect conservation. Grozinger studies health and social behavior in bees and is developing comprehensive approaches to improving pollinator health and reduce declines.
Among the speakers is Rachel Vannette, assistant professor, UC Davis Department of Entomology and Nematology, who will discuss her hummingbird research.
Wednesday, July 17
- 6:30 to 8 p.m.: Early Registration and welcome reception in the Good Life Garden at the Robert Mondavi Institute, 392 Old Davis Road, Davis.
Thursday, July 18
6:45 to 8:30 a.m., breakfast at Segundo Dining Commons
8:45 a.m. Opening remarks and welcome
9 a.m. Keynote Address: "The Importance of People in Pollinator Conservation" by Lynn Dicks, School of Biological Sciences, University of East Anglia, UK
10 a.m. Session 1: Novel Quantitative Methods in Pollinator Ecology & Management
- "The Role of Bee and Non-Bee Pollinators in Australian Open and Protected Cropping Systems (How do we overcome the pollination challenges?)" - Romina Rader, University of New England, Australia
- "Implementing a Honeybee Foraging Model and REDAPOLL Fruit Set Predictions in Washington State's Decision Aid System" - Vince Jones, Washington State University
- "Using DNA metabarcoding techniques to improve plant-pollinator interaction networks" - Victoria Reynolds, University of Queensland, Australia
- "Citizen Science Data for Mapping Bumblebee Populations" - Claudio Gratton, University of Wisconsin
11:15 to 11:30: Break (Light refreshments in the foyer)
- "From Theory to Practice: The Bumble-BEEHAVE Model and its Application to Enhance Pollinator Friendly Land Management" - Matthias Becher, University of Exeter, UK
- "A Laboratory System to Study the Effects of Stressors on Honey Bee Health and Fecundity" - Julia Fine, USDA-ARS Davis, Calif.
- "Using Automated Tracking to Link Individual Behavior to Colony Performance in Bumble Bees" - James Crall, Harvard University
Lunch at Segundo Dining Commons (opens from 11:30 a.m. - 1:30 p.m.)
1:45 p.m. Session 2: Drivers of Host-Pathogen Interactions
- "DWV as a Driver of Host Bee Decline" - Robert Paxton, Martin-Luther University, Germany
- "Novel Transmission Routes and Intensification as Drivers of Disease Emergence and Virulence in Honey Bee viruses" - Mike Boots, UC Berkeley
- "Viral Transmission in Honey Bees and Native Bees Supported by a Global BQCV Phylogeny" - Elizabeth Murray, National Museum of Natural History, Smithsonian Institution
3 to 3:15: Break (Light refreshments in the foyer)
- "Drivers of Pathogen Distributions in Feral and Managed Honey Bees" - Panuwan Chantawannakul, Chiang Mai University, Thailand
- "Serratia marcescens, a Pathobiont of Honey Bees?" - Kasie Raymann, University of North Carolina Greensboro
- "Foreign Fungi in Native Bees across the Commonwealth of Virginia" - Kathryn LeCroy, University of Virginia
- "Traits as Drivers of Plant-Pollinator-Pathogen Networks" - Quinn McFrederick, UC Riverside and Scott McArt, Cornell University
4:30 p.m.: Poster Session 1 in the ARC Ballroom
- 6:30 to 8 p.m. Opening Reception
Robert Mondavi Institute Sensory Building, 392 Old Davis Road, Davis
Honey Tasting led by Amina Harris, director, Honey and Pollination Center
Friday, July 19
6:45 a.m. to 8:30 a.m., Breakfast at Segundo Dining Commons
9 a.m. Keynote: "Bee Nutritional Ecology: From Genes to Landscapes," by Christina Grozinger, Penn State University
10 a.m. Session Three: Variable Climates and Changing Pollinators
- "Bee Responses to Climate Change: from Micro- to Macroecology" - Jessica Forrest, University of Ottawa, Canada
- "A Climate Vise of Temperature Extremes May Explain Past and Predict Future Bumble Bee Range Shifts" - Michael Dillon, University of Wyoming
- "Climate Change Effects on Megachilidae Bee Species along an Elevation Gradient" - Lindsie McCabe, Northern Arizona University
10:15 to 11:05: Break (Light refreshments in the foyer)
- "Testing the Phenological Mismatch Hypothesis for a Plant-Pollinator Iinteraction" - Charlotte de Keyzer, University of Toronto, Canada
- "Phenological Mismatch between Bees and Flowers Early in the Spring and Late in the Summer" - Gaku Kudo, Hokkaido University, Japan
- "Climate Change Impacts on Brazilian Pollinators" - Tereza (Cris) Giannini, Federal University of Para, Brazil
- "Pollinator Health in a Commercial Blueberry System" - Lief Richardson, University of Vermont
Lunch at Segundo Dining Commons (opens from 11:30 a.m. - 1:30 p.m.)
Optional Discussion: How do you relate your science to justice, equity and advocacy issue
1:45 Session 4: Causes and Consequences of Pesticide Use: From Use Patterns to Pollination Services
- "A New Framework for Environmental Risk Assessment of Pesticides" - Francisco Sánchez-Bayo, University of Sydney, Australia
- "Potency Paradox: Patterns and Drivers of Insecticide Use in U.S. Agriculture" - Maggie Douglas, Dickinson College
- "Estimating Pollinator Pesticide Exposure" - Maj Rundlof, Lund University, Sweden
Break (Light refreshments in the foyer)
- "A Risk Assessment of Neonicotinoid Insecticides in New York" - Travis Grout, Cornell University
- "Risk of Exposure in Soil and Sublethal Effects of Systemic Insecticides Applied to Crops on Adult Female Ground-Nesting Bees Using the Hoary Squash Bee as a Model Species" - D. Susan Willis Chan, University of Guelph, Canada
- "Delayed Lethality: The Effects of a Widely-Used Fungicide on Honey Bees (Apis mellifera)" - Adrian Fisher II, Arizona State University
- "Sub-lethal Impacts of Pesticides on Bees" - Troy Anderson, University of Nebraska
Poster Session 2 and Networking at the ARC Ballroom
Saturday, July 21
8 a.m. Registration at the ARC Ballroom
6:45 a.m. to 8:30 a.m.: Breakfast at Segundo Dining Commons
9 a.m.: Session 5: Integrative Approaches to Improving Bee Health Across Landscapes
- "Combining Physiological and Ecological Data for More Effective Bee Protection and Conservation" - Cedric Alaux, INRA, France
- "Keeping Bees in a Warming World: Protein Biomarkers for Heat Stress and Queen Failure Diagnostics" - Alison McAfee, North Carolina State University
- "Factors Influencing Colony Survival in Migratory Beekeeping Based on Honey Bee Resistance Traits" - Michael Simone-Finstrom, USDA-ARS, Baton Rouge, Louisiana
- "Temporal and Spatial Dynamics of Pollinator Communities across North Carolina Agroecosystem" - Hannah Levenson, North Carolina State University
- "The Effects of Land Cover on Habitat Quality for Nesting Bumble Bees" - Genevieve Pugesek, Tufts University
10 to 10:15 a.m. Break (Light refreshments in the foyer)
- "Improving Bee Health in Canola Pollination" - Shelley Hoover, Alberta Agriculture and Forestry
- "Mitigating Land Use Decisions that Destroy Bee Forage" - George Hansen, Foothills Honey, Oregon, USA
- "Impact of Landscape-Scale Floral Resources Availability on Pollinator Communities" - Aaron Iverson, Cornell University
- "Why are Crops Mainly Visited by Broadly Polylectic Bee Species?" - Katja Hogendoorn, The University of Adelaide, South Australia
1:40: Session 6: Pollinators in Urban Environments
- Presentation by The Wonderful Company
- Honoring new California Master Beekeeper graduates - Elina Niño, UC Davis
- "Floral Trophic Ecology of a North American Metropolis Revealed by Honey Bee Foraging Assay" -
Doug Sponsler, Penn State University
- "Pollinators and Urban Warming: A Landscape Physiology Approach" - Elsa Youngsteadt, North
Carolina State University
- "Green Infrastructure to Support Urban Wild bees: Communicating Science to Practitioners" - Scott
McIvor, University of Toronto, Canada
- "Urban Pollinator Conservation Opportunities: Integrating Research with Policy and Practice" -
Katherine Baldock, University of Bristol, UK
- "Linking Pollinator Health, Microbiome Composition and Human Provisioning in Anna's Hummingbird
(Calypte anna) - Rachel Vannette, UC Davis
Break (Light refreshments in the foyer)
- "Beekeeping Ordinances: Protecting bees and Neighbors" - Tracy Ellis, San Diego County
Department of Agriculture
- "Beekeeping in the City: Successes and Challenges" - Charlie Blevins, San Francisco Beekeepers'
- "Electric Power Companies Protecting Pollinators" - Jessica Fox, Electric Power Research Institute,
- "The Effect of Land use on a Sexually Selected Characteristic of the Cabbage White Butterfly (Pieris
rapae) in the United States" - Anne Espeset, University of Nevada, Reno
- "Urban Pollinator Conservation: Bee Campus USA and Bee City USA as a Model for Meaningful
Community Engagement" - Phyllis Stiles, Xerces Society for Invertebrate Conservation, Portland,
(There are no plans to video record the conference)
DAVIS--If you're like many Americans, you've set up a hummingbird feeder in your yard to nurture and watch these high-energy pollinators. But are you concerned that the sugar water you provide might be impacting your tiny feathered friends?
Newly published research indicates that sugar water in hummingbird feeders can contain high densities of microbial cells but “very few of the bacteria or fungi identified have been reported to be associated with avian disease,” says community ecologist and co-author Rachel Vannette of the University of California, Davis.
The research, published in the Proceedings of the Royal Society B, is one of the first to explore the microbial communities that dwell in sugar water from feeders and compare them to those found in flower nectar and samples from live hummingbirds.
“The potential for sugar water from hummingbird feeders to act as a vector for avian pathogens--or even zoonotic pathogens--is unknown,” said Vannette, an assistant professor in the UC Davis Department of Entomology and Nematology. “Our study is one of the first to address this public concern. Although we found high densities of both bacteria and fungi in sugar water samples from feeders, very few of the species of bacteria or fungi found have been reported to cause disease in hummingbirds.”
“So although birds definitely vector bacteria and fungi to feeders, based on the results from this study, the majority of microbes growing in feeders do not likely pose significant health hazards to birds or humans,” Vannette said. “However, a tiny fraction of those microbes has been associated with disease, so we encourage everyone who provides feeders for hummingbirds to clean their feeders on a regular basis and to avoid cleaning feeders in areas where human food is prepared.”
The paper, “Microbial Communities in Hummingbird Feeders Are Distinct from Floral Nectar and Influenced by Bird Visitation,” is the work of first author Casie Lee, a UC Davis School of Veterinary Medicine student; Professor Lee Tell of the UC Davis School of Veterinary Medicine's Department of Medicine and Epidemiology; Tiffany Hilfer, an undergraduate student and Global Disease Biology major; and Vannette.
Lee, mentored by Vannette and Tell, led the field experiment and performed bird observations and laboratory work during a summer project funded by the Students Training in Advanced Research (STAR) and Merial Veterinary Scholars Programs.
The researchers also compared the microbes in the feeders to those in floral nectar and found they differed in microbial composition.
“Birds, feeder sugar water, and flowers hosted distinct bacterial and fungal communities,” they wrote in their abstract. “Floral nectar and feeder sugar water hosted remarkably different bacterial communities; Proteobacteria comprised over 80% of nectar bacteria, but feeder sugar water contained relatively high abundance of Firmicutes and Actinobacteria, as well as Proteobacteria. Hummingbird feces hosted both bacterial taxa commonly found in other bird taxa and novel genera including Zymobacter (Proteobacteria) and Ascomycete fungi.”
The UC Davis scientists conducted their research at a private residence in Winters, attracting two hummingbird species, Calypte anna (Anna's Hummingbird) and Archilochus alexandri (Black-chinned Hummingbird) to drop net feeder traps. They mixed bottled water with conventional white granulated sugar (one part sugar and four parts water).
The researchers assigned feeders to one of three treatments including (1) access by both hummingbirds and insects (open feeders), (2) restricted access by birds but access by insects allowed (caged feeders, 1.5 cm square mesh), or (3) restricted access by both birds and insects (feeders bagged using gallon paint strainer bags), with two replicates of each treatment set up at each site, and the setup was replicated four times throughout the summer.
They examined and characterized microbial communities on bills and fecal material of the two species, as well their food resources, the feeder sugar water, and floral nectar. They tested sugar water from feeders that were visited and not visited. Results indicated that “both accumulated abundant microbial populations that changed solution pH and bird visitation rates.” Although both feeder sugar water and flowers contained aerobic, sugar-loving bacteria, they found that floral nectar contained mostly bacteria found only in flowers (Acinetobacter and Rosenbergiella) while feeder sugar water contained generalist bacteria that grow in many types of aqueous environments.
In pointing out that the microbial populations in the feeders differed from those in natural floral nectar, the UC Davis scientists noted that “human provisioning (of sugar water in feeders) influences microbial intake by free-ranging hummingbirds; however, it is unknown how these changes impact hummingbird gastrointestinal flora or health.”
As part of the study, they also performed a small experiment to assess how water type influences microbial growth. When feeders were exposed to birds, they found that deionized water supports the most fungal growth while tap water or bottled water supports the most bacterial growth.
“The microbes that hummingbirds are eating depends a lot on bird diet-- if they have access to feeders or are just consuming floral nectar,” Vannette said. “We don't know what the consequences are for bird health or gastrointestinal flora but we think that there should be more studies examining this, as many, many people use feeders, and the birds are opportunistic and drink from feeders!”
Hummingbirds (family Trochilidae) are one of the world's few avian pollinators. “Nearly 15% of hummingbird species are threatened or endangered,” the scientists related, so “understanding drivers of health and population dynamics may help conservation efforts. Avian microbial associates are just beginning to be studied in depth.”
Professor Tell said that “although our study does not directly inform hummingbird health outcomes, shifts in microbial composition in bird diets may influence bird microbiomes as a consequence. In the future, it will be important to understand how consumed microbial populations could potentially influence the health of free ranging hummingbirds, particularly with regards to anthropogenic effects on wildlife.”
Tell emphasized that the ideal human-provisioned food source for hummingbirds is floral nectar. “However, if feeders are offered, best practices entail routine and thorough cleaning that does not result in harmful residues,” she said.
Lee, who previously worked in wildlife rehabilitation and studied ecology before enrolling in the UC Davis School of Veterinary Medicine, commented: “I was very excited to work on a project that examined health of backyard wildlife in the context of modern society and grateful to have done it in the company of such hummingbird enthusiasts.”
Vannette was recently named one of 11 campus recipients of Hellman Fellowship grants, awarded to assistant professors who exhibit potential for great distinction in their research. Her project, “Characterizing the Structure and Function of Pollinator Microbiomes,” involves investigating the communities of bacteria and fungi in flowers and pollinators, including bees and hummingbirds. “Our work to date suggests that microbes in flowers are common and influence pollinator behavior,” she said.