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.

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.

Florida’s Bats: Southeastern myotis

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Holocene vertebrates from a dry cave on Eleuthera Island, Commonwealth of The Bahamas

We report a mid- to late-Holocene, non-cultural vertebrate assemblage from Garden Cave (site EL-229), Eleuthera Island, The Bahamas, with 2450 fossils representing 26 species. The chronology is based on accelerator mass spectrometer (AMS) radiocarbon (14C) dates determined directly on individual bones of the hutia ( Geocapromys ingrahami), an extirpated species of rodent that dominates the bone assemblage at Garden Cave. Four AMS 14C dates from our excavation range from 1340 to 1280 cal. BP (surface of the site) to 4860 to 4830 cal. BP with depth. A hutia bone lying on the surface from elsewhere in the cave dated to 450 to 290 cal. BP, which is roughly the time of European and African contact on Eleuthera. Other extirpated species from Garden Cave are tortoise ( Chelonoidis sp.), rock iguana ( Cyclura sp.), skink ( Mabuya sp.), parrot ( Amazona leucocephala), crow ( Corvus nasicus), and southeastern myotis ( Myotis austroriparius). Each of these species may have survived on Eleuthera until sometime after the initial human occupation of the island (~1000 cal. BP), although we have direct AMS 14C dates for only the hutia. During the time of fossil deposition in Garden Cave, sea levels were approaching that of today, yet land areas were considerably larger than now, connecting Eleuthera to New Providence, and potentially to Exuma as well. Such relatively recent connections are important in explaining past and present distributions of terrestrial plants and animals.

Structure and Reproductive Patterns in the Summertime Forest-Bat Community of Southeastern Texas

Forests of eastern Texas represent the westernmost extent of the southern pine forests and part of the pine belt of the forested Gulf coastal plain. Bat community assemblages in similar forests throughout southeastern United States have been documented in various studies, but only scant data are available for Texas. The purpose of this study was to characterize the assemblage and investigate reproductive patterns of the summer bat community in the austroriparian forest of eastern Texas. Using mist nets, we captured bats during summers 2009–2011 and recorded species, gender, age and reproductive condition. We captured 382 bats of eight species: Seminole Lasiurus seminolus (n = 163), evening Nycticeius humeralis (n = 86), big brown Eptesicus fuscus (n = 57), eastern red Lasiurus borealis (n = 31), southeastern myotis Myotis austroriparius (n = 21), tri-colored Perimyotis subflavus (n = 19), Mexican free-tailed Tadarida brasiliensis (n = 4), and hoary Lasiurus cinereus (n = 1) bats. Analysis of reproductive data suggests that three of these species (big brown, evening, and Seminole bats) may be following a reproductive strategy—extended seasonal monoestry (births of single litters spanning a particular season)—different than their previously reported pattern of synchronous monoestry.