Notes from the Field: What’s on a sparrow’s dinner menu?
“Notes from the Field” are contributed articles that highlight current banding projects and the continued importance of bird banding 100+ years after the establishment of the Bird Banding Lab. This article focuses on sparrows and how scientists are utilizing new tools to ask the age-old question: What’s for dinner?
“Notes From the Field” news articles highlight the continued importance of bird banding. This article was contributed by Tabitha Olsen who is currently working on her PhD dissertation examining the diet of sparrows wintering in the post-oak ecoregion of Texas.
Today, banding allows scientists to investigate bird behavior, migration, lifespans, populations, diseases and levels of environmental contaminants. Information gathered through the North American Bird Banding Program helps inform management and conservation decisions for game and non-game species, such as protecting or restoring habitat, setting hunting regulations and determining plans for human-led development. The North American Bird Banding Program depends on a network of over 10,000 permitted bird banders working in the United States, Canada and Trust Territories. Each year these banders help us add up to 1.2 million new banding records to our century-long dataset.
What is your bird banding/marking project?
As part of a larger PhD dissertation, we are examining the diet of sparrows wintering in the post-oak ecoregion of Texas. This study will take place during the winter season of November 2024-March 2025 and November 2025-March 2026. We use mist-nets to capture sparrows to collect morphometric data and a fecal sample to assess diet. To obtain the fecal sample, the birds are placed in paper bags, with a sterile platform for them to stand on. Once the birds are banded, measured, and a sample is collected, they are released.
How/why was this project started? What question(s) are you trying to answer through your research?
During the winter in Texas, the distribution of migratory sparrows such as White-throated Sparrows (Zonotichia albicollis), Field Sparrows (Spizella pusilla), and Melospiza sparrows (Lincoln’s Sparrow [M. lincolnii], Swamp Sparrow [M. georgiana], Song Sparrow [M. melodia]), overlap. These species often utilize many of the same habitats during the winter and inadvertently interact. Since these sparrows are similar in how they forage and what they consume, we wondered how they minimized competitive interactions. By examining diet, we aim to quantify the dietary breadth of each wintering sparrow species, as well as determine the level of dietary overlap or partitioning that occurs between interacting sparrows. We can extract DNA from fecal samples and obtain a detailed look of what individuals are consuming. We predict that sparrows will display high overlap at broad taxonomic levels (e.g., the consumption of seeds, plants, and invertebrates), but display some partitioning in the specific species of organisms being consumed or even in the proportions consumed. Additionally, we are using physical measurements of individuals (e.g., bill depth, tarsus, wing chord, etc.) to determine whether any divergence in diet is reflected in physical differences.
How does banding/marking help you answer your research questions and achieve objectives?
Each sparrow we capture and sample is banded with a metal USGS band, which allows us to make individual-level assessments of diet and morphology. Individual-level comprehensive diet analyses are traditionally difficult to conduct without lethally harvesting individuals. However, by banding and collecting fecal samples, we are able to non-invasively sample birds and still achieve fine taxonomic resolution of samples. Additionally, since each bird is individually marked, we are able to re-capture and re-sample individuals to obtain data at multiple time-points to monitor changes in diet.
What have you found so far? Any surprises? Major accomplishments?
While our first field season is still ongoing, we have banded and collected fecal samples from over 120 sparrows, including White-throated, White-crowned (Zonotrichia leucophrys), Lincoln’s, Song, Swamp, Vesper (Pooecetes gramineus), Chipping (Spizella passerina), and Savannah Sparrows (Passerculus sandwichensis). Additionally, we’ve collected fecal samples from an Eastern Towhee x Spotted Towhee hybrid (Pipilo erythrophthalmus x P. maculatus), a hybrid that is suspected to be common in our region of Texas but is generally under-recorded. This project is extremely early in its development and is currently in the sample collection phase. However, we are excited to begin the next phase of DNA extraction in the coming months.
What are the next short- and long-term steps for your research project? What questions remain or what new questions have been raised by what you have found so far?
As we proceed through our field season, we are interested in examining specialization of individual birds as well as species. Our data are unique, as banding allows us to identify individuals, so we can quantify the variability of diet within each population as well as over time through recapture samples. We hope to further expand this idea in our examination of White-throated and White-crowned Sparrows, both of which are generally understood to be generalist foragers, how variation in diet measured among individuals influences the diversity in diet measured within populations or species.
Why is your study species particularly interesting?
Sparrows (or ‘little brown birds’ as some refer to them) are often overlooked by bird watchers and the public due to their tendency to be present everywhere, having song and call similarities, and their brown, drab appearance. However, sparrows are hidden gems that allow us to formulate seemingly simple questions such as “What do they eat?” into complex answers regarding competition, niche establishment, and community interactions. These migratory, ‘little brown birds’ are often the first faces of winter for our region of Texas. With a deeper understanding of winter diet dynamics, they may become faces of conservation for the post-oak savanna and its associated flora and fauna.
Who is involved in your project (individuals, university, partners, collaborators)?
This project is a chapter of a larger PhD dissertation and is affiliated with Texas A&M University. Specific individuals involved with the project include:
- Tabitha Olsen (PhD student who designed the project for her dissertation)
- Dr. Christopher Butler (Lab PI)
- Inland Bird Banding Association (Funding)
- Schubot Center for Avian Health (Funding)
How long have you been working in biology? How long have you been banding or marking birds? How has bird banding/marking changed over the course of your career or during this project?
I have been banding birds since 2018 when I was an undergraduate student in the Department of Forestry and Natural Resources at Purdue University. During that period, I co-led the University’s Northern Saw-whet Owl (Aegolius acadicus) Banding Station where we focused on undergraduate skill-building, community engagement, and individual project development. Since then, I have been working in the avian ecology field for my entire career, including my Master’s and now my PhD. Banding birds has been a consistent part of my career, whether it be owls, rails, or passerines.
Why do you think projects like yours are so important?
Everyone needs to eat something, but organisms cannot typically eat everything that is within their environment. Improving our understanding of how organisms utilize the world around them helps us to better connect habitat use to the species of interest. Diet is a fundamental part of an organism’s life and ecology and, until recently, a fine-scale assessment of how and what individuals consume has been difficult to obtain. Studies like this are an example of how new tools can be used to ask age-old questions: What’s for dinner?
Where can I get more information about your project (project website, publications etc.)?
You can receive more information and updates regarding this project at Tabitha Olsen’s ResearchGate or her OrcID. Publications will be added to these sites as they are released.
Is there anything else you think is important to mention about your project/research?
We are grateful for the support of the Inland Bird Banding Association and the Schubot Center for Avian Health for providing funding for this work.
Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
All banding, marking, and sampling is being conducted under a federally authorized Bird Banding Permit issued by the USGS BBL.
The “Notes From the Field” series highlights current banding projects and the continued importance of bird banding and the Bird Banding Lab. Want to see your project featured in a future “Notes From the Field” article? Email Kyra Harvey kharvey@usgs.gov for submission details.
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