Results were complex and illustrate that bat activity and species richness are impacted by a wide variety of factors, with structural and contextual characteristics, such as clutter and habitat type, having the greatest impact. Best fitting models also mainly consisted of many variables with each one making a small contribution instead of one variable contributing the most. While our models are large for best fitting regression models, they had lower AICc and higher R2 values than all alternate models with less variables. Our models show the habitat variables most associated with bat species richness and activity at multiple scales. While similar results from other studies imply these factors in our best-fitting models are likely important in multiple areas (Adams et al. 2009; Bader et al. 2015; Bailey et al. 2019; Blakey et al. 2017; Buckman-Sewald 2014; Campbell et al. 1996; Evelyn et al. 2004; Gaisler et al. 1998, Hollen 2017; Jung et al. 2012; Lintott et al. 2015; Medinas et al. 2019; Put et al. 2019; Rainho et al. 2010, Yoshikura et al. 2011), our results may not apply to all areas, so more research is needed to confirm generalizability, especially since no specific variable contributed a particularly large amount any one model.
Variables that were important at one scale were often not important at another. For instance, variables that were strongly associated with bat activity or species richness at 100 m were often not associated with it at 500/250 m (e. g. perennial ponds), and vice versa. This supports previous findings that it is important to use multiple spatial scales by Gallo et al. (2018), who found that different variables were important at 50 m, 500 m, and 1 km scales. There may be a difference between 100 m and 250/500 m buffers but not 250 and 500 m buffers because 100 m buffers are closer to local scale than 250 and 500 m ones. For instance, number of habitat types was important in 250/500 m buffers but not 100 m ones. The number of habitat types was positively associated with species richness and activity along roads, which indicates that habitat heterogeneity is positively associated with bat activity along roads. This may be because bat species found foraging along roads tend to be more fragmentation tolerant and prefer to forage along habitat edges, such as hoary bats (Barclay 1985, Hollen 2017). This variable being more important at only larger size buffers implies a more large scale effect of this variable.
Bat activity was also not evenly distributed across the region. Survey points with agricultural habitat on at least one side of the road tended to have lower bat activity and species richness than those without agricultural cover and points with natural habitat on at least one side of the road generally had higher activity and species richness than those without natural habitat. Furthermore, spots of the least bat activity were clustered in the part of the region with the most agriculture. Previous studies also found that bats generally avoided areas with high agricultural cover (Blakey et al. 2017; Put et al. 2019). Most of the agriculture in the region consists of large row crop monocultures, but previous research showed that increasing farmland heterogeneity or using organic farming methods is beneficial to bat activity and diversity. If possible, encouraging local farms to diversify their crops, plant tree rows, or use organic methods could help bats (Monck-Whipp 2018; Wickramasinghe et al. 2003) and retaining natural field or forest habitat alongside the road on at least one side would also be beneficial in managing for ideal bat habitat. Both natural open and forested habitats were beneficial for bats, although the type of forest mattered to some extent.
Open habitats such as savanna and upland prairie and total forest were positively associated with activity and/or species along transects. While savanna habitats have increased in cover in recent years due to restoration efforts (Martin and Root 2020), additional restoration may be beneficial. Buckman-Sewald (2014) found higher activity of hoary bats, one of the most common species along transects, in savanna habitats. This may be contributing to higher activity in areas of more savanna cover along transects, as the lack of clutter from tall woody vegetation in these habitats likely make them easier for open-adapted bat species to forage in. Previous studies also found a significant positive impact of total forest cover along roads and developed areas, although there is some variability based on species (Evelyn et al. 2004; Medinas et al. 2019). Conifers were the only type of forest that was negatively associated with bat activity, which may be because most conifer cover in the area is farmed monotypic stands (Abella 2010, Abella et al. 2017). The finding that higher percent conifers was associated with lower activity and species richness is consistent with previous studies (Buckman-Sewald 2014, Hollen 2017, Yoshikura et al. 2011). Natural habitat with diverse vegetation appears to be most beneficial for bats.
For clutter, whether the impact was positive or negative depended on the height level. Both species richness and bat activity were negatively associated with clutter at 3-6.5 m along transects. This supports previous findings that bats avoid areas of higher vegetation clutter and taller understory cover (Adams et al. 2009; Campbell et al. 1996; Lintott et al. 2015; Rainho et al. 2010). However, there were positive associations with clutter 0–3 m with species richness and activity along transects. This is likely because open habitats associated with higher bat activity and species richness, such as savanna and upland prairie had higher clutter at the lower height level and less clutter at the higher height level, which is ideal for open foraging species, the most common group along transects. These results suggest that it would be advantageous for open foraging bats if land managers reduce clutter at the 3-6.5 m level and increased low level vegetation along roads. Other structural variables, such as clutter, were also important.
There was a positive association between canopy height and species richness and between average percent canopy cover and total activity. Previous studies have also found positive associations between canopy height and cover and bat activity, especially along roads (Bader et al. 2015; Bailey et al. 2019; Jung et al. 2012; Russell et al. 2009). This indicates that planting tall trees along roads potentially could be beneficial for bats.
Higher percent of ponds in 100 m buffers was significantly correlated with higher species richness along transects. Combined with the positive association between months water observed at transect and species richness, this indicates that water could be important to a diverse bat community along roads. This is consistent with past findings (Gaisler et al. 1998). It is worth noting that number of months where water was recorded was only recorded in 2021, while previous years whether ditches were present was only noted once a season (if ditches were present once, they were noted as present every month for those years), so that may have impacted results.
Some species foraged along roads more than others. Northern long-eared bats were never found along transects and little-brown bats and tri-colored bats very rarely were. These three species were located more frequently, although they were still rarer than other species, during surveys in protected parks in the same region during the same period (Russo-Petrick 2022). All three of these species are of conservation concern, so this indicates that roadside habitats are not preferred by these species. While some variables were consistently important, the variety in results and that no one variable had an especially large contribution to models shows how complicated the question of what habitat factors impact bats is and how much results can vary when multiple scales are considered. This may be because we examined all species together, and responses are species specific or differ between forest and open habitat specialist guilds. Comparing results between open and forest specialist guilds at stationary points revealed differences in habitat preferences between the groups and less variables were used in those models, but forest specialist activity along transects was too low compared to open specialists to do similar models for transects (Russo-Petrick 2022). Because of the complicated nature of bat community responses, looking at guild or species-specific responses may be beneficial in the future if there are enough calls to do so.