By Johnny Baakliny, MW CASC Graduate Student Fellow
October 28, 2024
The land surrounding the Indianapolis International Airport, once a rich mosaic of forests, wetlands, and swamps, has undergone a significant transformation over the past three decades due to extensive urbanization. Once prime habitat for wildlife, it is now dominated by warehouses, concrete runways, and roads, with human development carving away at the natural landscape. This area has seen its ecosystem drastically altered, leaving little of the original environment intact. Yet, despite these sweeping changes, the endangered Indiana bat (Myotis sodalis) has exercised an unexpected form of agency, becoming central in conservation efforts in this area.
In the 1990s, plans to extend the airport threatened critical maternity roosts, where female Indiana bats gather to give birth and raise their pups during the summer months, typically in dead tree cavities or under loose bark. This led to the creation of conservation easements—sections of land designated specifically to mitigate the impacts of urban development on the species. The bats' presence was instrumental in reshaping the development plans, compelling stakeholders to acquire land for mitigation, initiate reforestation projects, and install artificial roost structures. The bats' reliance on these maternity roosts essentially redefined how the land could be used. Our lab has closely monitored this population. Bat boxes were deployed in phases as the natural habitat became more fragmented and degraded, providing the colony with crucial alternative roosts. Over time, these artificial structures have become integral to the bats' survival in this modified landscape, and today the population has grown from around 100 bats to more than 600.
This summer, my research focused on understanding the roosting behavior and movement patterns of this maternity colony. Using a combination of spotlight checks, emergence counts, and acoustic surveys, I aimed to assess the behaviors of bats using the bat boxes. We wanted to determine the timing of use and whether these structures alone could support the growing population or if additional roosting options were necessary. Previous research led by Joseph Petit and Joy O’Keefe found that the day of the year, particularly changes in day length, was the main predictor of Indiana bat migration timing, meaning bats were expected to arrive and depart around the same time each year. This timing was also influenced by weather conditions and temperatures. That study, based on 17 years of data from the same maternity colony, revealed that bats typically depart in early October, though warmer autumns can extend their stay. This work provides valuable context for understanding the shifts we’ve seen in migration timing, particularly as climate change alters environmental cues.
While the typical departure date for Indiana bats at this site is around October 7, this summer I observed two individuals still roosting in two boxes on October 17. While Pettit and O’Keefe recorded the latest migration date as October 31, this year’s delay raises important questions about the factors that might drive late departures. Climate change, as Pettit suggested, could be extending the bats’ foraging opportunities, or perhaps other environmental conditions are influencing the timing of their migration. The presence of these two late-departing bats underscores the importance of continued monitoring. As climate change continues to affect seasonal temperatures, the timing of Indiana bat migrations could shift in unpredictable ways. Warmer falls could mean longer stays in summer roosts, which could necessitate changes to the timing and nature of conservation and management practices for this endangered species.