Sexual size dimorphism and geographic variation in forearm length of Rafinesque’s Big-eared Bat (Corynorhinus rafinesquii) and Southeastern Myotis (Myotis austroriparius)

Sexual size dimorphism is common in many taxa and results from various pressures, including competition, reproductive requirements, functional differences, and sexual recognition. For mammals, males are typically the larger sex; however, for vespertilionid bats, females are more often the larger sex. Forearm length, a feature that influences overall wing and body size and is often sexually dimorphic, is a standard morphological measurement taken from bats. Forearm length was measured in two vesper bat species (Corynorhinus rafinesquii and Myotis austroriparius) that co-occur across much of the southeastern United States. Forearm length was greater in females of both species, and females of both species also exhibited regional variation in forearm length. By having a longer forearm and therefore being larger in size, females may be more maneuverable and better equipped to carry young. While this study did not directly investigate the mechanisms behind regional variation in forearm length, it is possible this is the result of variability in habitat types, resources, or thermodynamic constraints. Knowledge of sexually dimorphic characteristics is important for obtaining a general understanding of a species and its morphology.

Feasting, not fasting: winter diets of cave hibernating bats in the United States

Temperate bat species use extended torpor to conserve energy when ambient temperatures are low and food resources are scarce. Previous research suggests that migratory bat species and species known to roost in thermally unstable locations, such as those that roost in trees, are more likely to remain active during winter. However, hibernating colonies of cave roosting bats in the southeastern United States may also be active and emerge from caves throughout the hibernation period. We report what bats are eating during these bouts of winter activity. We captured 2,044 bats of 10 species that emerged from six hibernacula over the course of 5 winters (October–April 2012/2013, 2013/2014, 2015/2016, 2016/2017, and 2017/2018). Using Next Generation sequencing of DNA from 284 fecal samples, we determined bats consumed at least 14 Orders of insect prey while active. Dietary composition did not vary among bat species; however, we did record variation in the dominant prey items represented in species’ diets. We recorded Lepidoptera in the diet of 72.2% of individual Corynorhinus rafinesquii and 67.4% of individual Lasiurus borealis. Diptera were recorded in 32.4% of Myotis leibii, 37.4% of M. lucifugus, 35.5% of M. sodalis and 68.8% of Perimyotis subflavus. Our study is the first to use molecular genetic techniques to identify the winter diet of North American hibernating bats. The information from this study is integral to managing the landscape around bat hibernacula for insect prey, particularly in areas where hibernating bat populations are threatened by white-nose syndrome.

Characteristics of caves used by wintering bats in a subtropical environment

Many cave-roosting bats are declining in number throughout their range because of multiple threats, including disease, disturbance by humans, and habitat loss. Successful conservation of cave-roosting bats requires an understanding of the roles of microclimate, cave structure, and the surrounding landscape on the distribution and abundance of bats, and in particular, the use of winter cave roosts. Cave bats have been well-studied in temperate climates, but we know little about these bats in subtropical climates. From 2015-2017 we conducted 399 winter surveys of 162 caves in Florida to evaluate factors affecting presence and abundance of bats at cave roosts. We also determined whether temperatures at these cave roosts were suitable for Pseudogymnoascus destructans, the fungus that causes white-nose syndrome. Across all 3 years, we detected three species of bats: tri-colored bats Perimyotis subflavus in 126 (77.8%) caves, southeastern myotis Myotis austroriparius in 51 (31.5%) caves, and a single Rafinesque's big-eared bat Corynorhinus rafinesquii. We analyzed presence of both tri-colored bats and southeastern myotis in caves using mixed-effects models with a binomial distribution and the number of tri-colored bats using generalized linear mixed-effects models with a Poisson error distribution. Tri-colored bat presence was significantly and positively influenced by a cooler cave surface temperature, larger cave entrance size, as well as a single entrance, and the presence of solution holes. Tri-colored bat abundance increased in longer, cooler caves that had solution holes, a single entrance, free of obstructions, and had no signs of flooding. Southeastern myotis presence was positively associated with longer, domed caves. To be most effective, conservation efforts in subtropical climates should focus on caves with the identified characteristics. More than 90% of caves surveyed each year had a cave interior surface temperature below the upper critical growth limit for P. destructans (19.8 °C), indicating that most Florida caves are suitable for growth of P. destructans. Therefore, regular monitoring of winter bat populations in subtropical caves may be important for detecting P. destructans or white-nose syndrome.

Habitat associations of Rafinesque’s big-eared bats (Corynorhinus rafinesquii) and their lepidopteran prey in bottomland hardwood forests

Effective conservation of forest bats requires knowledge of daytime and nocturnal habitat use. Although many bat species use different habitats during the daytime and nighttime hours, these data are rarely collected simultaneously. We radio-tagged 48 adult Rafinesque’s big-eared bats (Corynorhinus rafinesquii (Lesson, 1827)) in a bottomland hardwood forest in Kentucky from 2009 to 2011. We tracked bats to 64 day roosts over 549 bat-days and found bats roosted almost exclusively in trees located in forested wetlands (n = 59; 92%), and that reproductive females established their home ranges closest to these habitats (P < 0.0001). Although few (n = 4; 6%) roosts were located in deciduous forests on drier soils, these forests were important foraging habitats for pregnant females, which foraged closest to these habitats within their home ranges (P = 0.04). Abundance of Lepidoptera differed among habitats (P = 0.03), with higher abundance in deciduous forests and along forest–field edges. Deciduous forests were the only habitat preferentially selected by any lepidopteran family (Notodontidae), and the only habitat not avoided by any family. These data confirm the importance of forested wetlands to the ecology of Rafinesque’s big-eared bat and demonstrate the benefit of proximally located deciduous forests that provide habitat for their moth prey.