Bats, cities, and trees: The response of Midwestern bats to the urban forest gradient

The study of urban wildlife has grown within the past two decades. However, there are still significant gaps in our knowledge of the ecology of bats living in cities. Namely, we know very little about how urban bat assemblages respond to their environment across contrasting urban areas, as cities may have stark differences in vegetation and land use regimes. Variation in bat responses across cities, or “between-city differences,” has not been investigated in North America, as previous urban bat studies have been conducted at the scale of a single, large city. Additionally, few studies have sought to examine fine-scale responses of bats to LiDAR-derived tree metrics despite their demonstrated utility in quantifying canopy structure. We sought to fill these knowledge gaps through two research projects. The first was the Bats in Small Cities (BiSC) Project, a 36-city acoustic survey of urban areas in the Midwestern United States to ascertain how occupancy by different groups of bats is related to between-city differences. We also sought to overcome the large-city bias by focusing on smaller cities. We showed that for the big brown bat and silver-haired bat acoustic group, increasing local tree canopy cover within a 100-m buffer around our survey points strongly predicted occupancy; however, this local effect was more robust in urban areas with lower city-scale tree cover. Additionally, local hoary bat occupancy was lower in cities with higher city-scale tree cover. Together, our results show that bats respond differently to local habitat patches depending on habitat at the city-scale. We recommend more multi-city monitoring of urban bat activity and diversity using long-term, spatially distributed monitoring efforts, which would also capture temporal patterns. In our second project, we placed acoustic monitoring devices on trees in the parks, forests, and neighborhoods of Champaign-Urbana, Illinois, to determine the effectiveness of LiDAR-derived metrics in predicting big brown bat and eastern red bat activity and documenting the bat species richness of the area. Both species responded positively to increasing horizontal canopy heterogeneity, defined as the standard deviation of the mean tree canopy cover, within a 50-m buffer around stationary survey points. However, this response depended upon interactions with other variables. For big brown bats, the positive effect of horizontal canopy heterogeneity was only significant within open park habitat or depended on the level of development within a 50-m buffer. For eastern red bats, the positive effect of horizontal canopy heterogeneity was only significant within forests. Additionally, we discovered that northern long-eared bats occur in the forests in the northeast part of the area. Modeling showed that northern long-eared bats were more likely to occur farther from roads, but this effect was more intense in areas with lower canopy cover within a 500-m buffer. Monitoring a single urban area with stationary devices revealed that LiDAR-derived metrics quantifying tree structure are informative in predicting urban bat response at a fine scale and that the Champaign-Urbana area is home to a diversity of bat species, including the endangered northern long-eared bat. We recommend future experimental studies testing bats' responses to manipulated canopy heterogeneity in urban areas. Overall, we conclude that trees are crucial for supporting bat activity and occupancy in urban areas throughout the Midwest, and this emphasizes the importance of maintaining urban tree cover to support bat conservation. We recommend further study that investigates how bats respond to applied urban forestry management practices and also recommend future study examining urban bat ecology at a continental scale, using multi-city approaches to examine regional differences in bat responses to urbanization.

Name thesis:degree_name

M.S.

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Natural Res & Env Sciences

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2024

Author dc:creator

• Obrochta, Sean Maclaine

Contributors dc:contributor

• O'Keefe, Joy M
• Benson, Thomas J
• Stickley, Sam
• Li, Han

• Bats
• Urban Ecology
• Acoustics
• Community Science
• Conservation

Statement dc:rights

• Copyright 2024 Sean Obrochta

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/125644

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F125644