Caretakers versus Exploiters: Impacting Biodiversity in the Age of Humans

Bat Biodiversity

Figure 2 The little brown bat (Myotis lucifugus) is one of 8 bat species commonly found in Connecticut.

There are over 1,400 species of bats, making their order, Chiroptera, one of the most diverse order of mammals in the world second only to rodents.  Bats are found on every continent except Antarctica, and their habitats vary from tropical, temperate, and boreal forests to deserts, grasslands, mountains, and caves.  The greatest bat biodiversity occurs along equatorial regions, with countries such as Indonesia and Columbia hosting nearly a third of the world’s bat species. ³ There are 8 species of bats in Connecticut, with the little brown bat (Myotis lucifugus) and the big brown bat (Eptesicus fuscus) being the most dominant.  In the winter, the northeastern bats hibernate in large colonies, which helps for warmth and reproduction, but can lead to rapid disease transmission.  In the spring, summer, and fall, bats will roost in small groups or even alone under building eaves, bridges, trees, rock formations, caves, wood piles, human-made bat boxes, etc. but not necessarily in the same location where they hibernate. 

Bats are unique amongst mammals, as they are the only mammal capable of flight.  Their forearms form wings with 25 moveable joints and are connected by a skin-like webbing with three extending fingers.  They can achieve thrust, and are capable of sustained, self-propelled flight.  Unlike feathered birds, bats have sensitive body hair that can detect small changes in air currents and breezes.  Their unique wing and body structures enable acrobatic, short-term flight that makes them skilled predators.  Bat species can vary significantly in size, from the 2-gram Kitti’s hog-nosed bat from Thailand and Myanmar that is about the size of a bumblebee, to the Indian Flying Fox, a 1.6kg (3.5 pound) creature with up to a 1.7m (about 6 foot) wingspan! Bats can also live a long time compared to mammals of similar size, with an average lifespan ranging between 10 and 30 years depending on the species.  A tiny male Brandt’s myotis bat from Siberia is the oldest bat ever documented at 41 years old! When it was caught in 2005, it still bore a numbered band that had been attached by researchers who first captured the bat in 1964.⁴

Figure 3 Flying foxes, large fruit eating mega bats from Indonesia.

Bats play an important role in a variety of ecosystems throughout the world through insect control, plant pollination, and seed dispersion.  Bat diets can be categorized into two main categories: insectivores and frugivores.  About 70% of bat species are insectivores, often eating moths, midges, beetles, mosquitoes, and other small insects.  The little brown bat can eat an estimated three times its body weight on a good night.

Most bats use echolocation to navigate and find insect prey. They emit ultrasonic sound waves at frequencies beyond human hearing.  These sound waves bounce off objects in their environment and return to the bat’s ears, who can then process the reflected sound to pinpoint even tiny insects in low light conditions. Sonar technology for navigating underwater and radar technology for using radio waves to navigate in open air are both technologies inspired by the bat’s use of echolocation.

Some bats will eat small fish, amphibians, and other bats.  There is only one species, the vampire bat from Central and South America, that feeds off the blood of small or grazing animals.  Frugivores prefer fruit but may also feed on flowers, nectar, and pollen.  Many of the large bat species are fruit eaters.  They are also very messy eaters, which is excellent for seed dispersal.  Bats that feed from nectar are excellent pollinators.  Over 300 plant species across a variety of ecosystems depend on bats for pollination, including bananas, peaches, durian, cloves, carob, balsa wood, agave, and the Saguaro cactus.

Bat fecal matter, guano, is also a nutrient rich fertilizer that contains a concentration of 10 percent nitrogen (N), 3 percent phosphorus (P), and 1 percent potassium or potash (K). High nitrogen levels in the soil are responsible for fast, green growth, while phosphorus helps with root and flower development. 

Bats in general do not have many natural predators.  Occasionally weasels, raccoons, rats, owls, snakes, or other opportunistic predators (even other bats) might catch and eat one, but they are not a primary part of any predator’s diet.  Humans in certain regions eat bats as well, often marketed as bushmeat.  Bats are also rather adaptable to coexisting alongside humans, even roosting in human structures.  In many cases in the Northeast USA, bats were considered a nuisance and were reason to call an exterminator – especially if a colony decided to roost in your attic or barn.  Today, due to the bat population decline, many extermination services offer removal and relocation as a preferred alternative. In states where bats have been listed as endangered, extermination is not an option.   

Bats can host a variety of diseases, some of which are zoonotic, or able to be transmitted from bats to humans and other animals. This has, unfortunately, been a point of contention in the relationship between people and bats.  The primary zoonotic diseases associated with North American bats are rabies, histoplasmosis, salmonellosis, yersiniosis and external parasites such as ticks, mites, and parasitic flies. Bats from other parts of the world can carry several zoonotic viruses including Nipah virus, Hendra virus, Ebola virus, SARS coronavirus and others which can cause severe and fatal illness in humans and other animals.  Bats are often referred to as viral reservoirs because they can carry and quickly spread over 60 known viruses.  Bats have an incredibly robust immune system and are not affected by most of the viruses they carry, where rabies virus is a notable exception.  When bats fly, they release a great amount of energy, which increases their body temperature to 38° to 41° C (100° to 106° F). The pathogens that have evolved in bats are able to withstand these high temperatures. This presents a problem for humans because our immune system has evolved to use high temperatures, in the form of fever, to disable pathogens.⁵  If these pathogens become resilient to higher temperatures, the resurgence of diseases and the human impact could be significant. 

Fortunately, the cases of bats infecting humans is extremely rare.  Bats almost always avoid human contact as much as possible.  According to the CDC, “rabies in humans is rare in the United States. There are usually only one or two human cases per year. But the most common source of human rabies in the United States is from bats. For example, among the 19 naturally acquired cases of rabies in humans in the United States from 1997-2006, 17 were associated with bats. Among these, 14 patients had known encounters with bats. Four people awoke because a bat landed on them and one person awoke because a bat bit him. In these cases, the bat was inside the home.”⁶

Another disease that is affecting bats and leading to a drastic decline in some bat populations, is a fungal pathogen called Pseudogymnoascus destructans, which produces a disease known as White Nose Syndrome (WNS).  The most dominate bat species in North America, Myotis lucifugus, commonly known as the little brown bat, has been facing an extinction level crisis due to WNS and will be the subject of the next section of this unit.