Overview
- Between 1995 and 2023, the City of Ann Arbor’s Natural Area Preservation (NAP) division coordinated a continuous butterfly monitoring program using trained community science volunteers. In 2024–2025, Ludovico Behrendt, an environmental data specialist with NAP, conducted a retrospective analysis of this nearly 30-year dataset, which includes over 16,600 butterfly observations collected across city parks. His work represents the most comprehensive analysis to date of long-term insect biodiversity trends in the Ann Arbor area and is one of the most sustained municipal-scale pollinator datasets in Michigan. The project aimed to understand how butterfly communities have changed over time and what those changes reveal about local habitat health, ecological management, and landscape conditions throughout Washtenaw County.
- The analysis found that butterfly abundance and species diversity in Ann Arbor’s natural areas remained relatively stable over the three-decade period. While year-to-year variability was expected, there were no significant long-term declines or increases in overall population levels, suggesting that these parklands have provided relatively stable habitat conditions over time—even as insect populations in other parts of the country have faced serious declines.
- Larger parks and those with greater habitat continuity were found to support higher levels of butterfly biodiversity. Sites with expansive and unfragmented green space—such as Barton Nature Area and Bird Hills—consistently hosted a wider range of species and greater individual abundance. This reinforces the ecological value of conserving large, connected natural areas within urban and suburban landscapes.
- Parks that included a variety of habitat types—such as a combination of prairies, wetlands, woodlands, and edge zones—also showed higher butterfly diversity. These structurally and botanically diverse environments were more likely to support both generalist species and habitat specialists, which often have specific host plant or microclimate requirements.
- Over time, parks that received more intensive ecological management by NAP showed measurable increases in both butterfly abundance and diversity. Practices like prescribed burning, invasive species control, and native plant restoration were associated with more robust pollinator populations, particularly in sites where these activities were applied consistently across multiple seasons.
- Since 2019, several habitat-specialist butterfly species—such as eastern tiger swallowtails, spicebush swallowtails, and monarchs—have shown significant increases across Ann Arbor’s natural areas. These species rely on diverse, high-quality flowering plant communities to reproduce and compete successfully with more aggressive generalist species like cabbage whites. Their increased presence in recent years serves as indirect evidence that flowering plant diversity has also improved, likely due to cumulative restoration efforts led by NAP.
- Although fireflies were not included in this study, the monitoring infrastructure and analytical framework developed through this butterfly program offer a strong foundation for future firefly monitoring efforts. Fireflies are increasingly reported to be declining in Michigan, and they face distinct threats such as habitat degradation, pesticide exposure, and especially artificial light at night. Adapting the community science model to track firefly populations would help establish long-term baselines, identify areas in need of dark-sky protections or wetland restoration, and support broader insect conservation strategies across Washtenaw County.
Transcription
David Fair: This is 89.1 WEMU, and I’m David Fair, and I have a question for you. What does a butterfly mean to you? Well, these creatures have the most fascinating life cycle and, from a community standpoint, can tell us a lot about the health of our environment and ecosystems. Welcome to this week’s edition of Issues of the Environment! The Ann Arbor Natural Area Preservation Division has been studying this issue for decades. It has continuously monitored the local butterfly population and recently did an analysis of what was found from 1995 to 2023. Our guest this morning headed up that analysis. Ludovico Behrendt is an environmental data specialist with NAP and thank you so much for the time today! I appreciate it!
Ludovico Behrendt: Thank you for having me on!…