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The Physiology of Bats Hannah Ruangsin

Table of Contents

  1. About Bats
  2. Nutrition
  3. Thermal Regulation
  4. Nervous System
  5. Sensory Processes
  6. Muscles
  7. Reproduction
  8. Navigation
  9. Excretion
  10. Other

About Bats

Bats are mammals who fall in the order known as Chiroptera. There are more than 1,400 species of bats, accounting for about a quarter of all mammals worldwide. Chiroptera is divided into two suborders, Megachiroptera and Microchiroptera, also known as megabats or microbats. The difference between megabats and microbats is their size, diet, and use of their senses. Microbats are echolocating while megabats strongly use their sight and smell to navigate. Although there are many negative misconceptions about bats, they are an important species to many ecosystems. They are pollinators, help disperse seeds, control insect populations, and produce nutrient-rich fertilizer. Bats are under appreciated and there is a lot more to be learned about them.

Nutrition

Bat diet varies within species and mostly depends on the climate of their environment. Megabats for example, are known as nectarivores and frugivores since their diet is plant-based. Nectarivores eat nectar and pollen while frugivores eat fruit. Microbats on the other hand are known as insectivores since many of them eat things such as flies, mosquitoes, and beetles. A small percentage of microbats drink blood from livestock, and they are called vampire bats. By using their tiny sharp teeth, vampire bats are able to cut their prey and lick the blood.

Thermoregulation

Unlike other mammals, bats are heterothermic rather than homeothermic. Bats use temporal heterothermy, which is also known as torpor (Stawski 2014). Torpor is a physiological change in which an animal reduces its body temperature and metabolism. Small endotherms such as bats, use torpor to save energy by "abandoning regulation of high body temperature (Stawski 2014)." It is important for bats to manage their energy efficiently due to the high cost of activities such as echolocation and flying.

Nervous System

With the exception to its ears and the ability to fly, the nervous system of bats also follows any other mammals. Bats use flight in order to hunt, migrate, breed, and avoid predators. They are the only free-flying mammal, and their enhanced echolocation allows them to fly at night. The structure of bat wings is different from that of birds or insects because they are made of skin rather than dead matter. Studies have shown that the unique properties of bat wings improve aerodynamic performance in terms of maneuverability and agility (Norberg & Rayner 1987). Although not fully understood yet, bat aerodynamics is also linked to the use of their tail membrane. Unlike other winged animals, bat tails and wings are connected to their legs. Studies have shown that "adjusting tail position by increasing the angle of the legs ventrally relative to the body has a two-fold effect; increasing leg-induced wing camber and increasing the angle of attack of the tail membrane (Gardiner 2011)."

Bat Wing

Sensory Processes

A unique feature of bats is that they use echolocation for navigation and hunting. Echolocation is the use of ultrasound waves produced by bats that bounce off objects in their surrounding. "By listening to how the echoes of their vocalizations are modified by objects in the environment, bats can localize stationary or moving objects in three dimensions and determine the object's size, shape, texture, and other characteristics (Covey 2005)." Only microbats use echolocation, which is why they have such big ears in comparison to megabats. The majority of microbats use echolocation in the form of laryngeal echolocation while a few others do it in the form of tongue clicks. Since echolocation in bats is so precise, "they may eat up to 50% of its body weight in insects every night, and nursing females may either their entire body weight -- about 4500 insects average (Fink 2007)."

Gray long-eared bat (Plecotus austriacus)

Besides a few, megabats do not echolocate and instead rely on their sharp sense of sight and smell for navigation. Megabats have large eyes that benefit their nocturnal ways. Their specific eye structure makes them sensitive to UV light but also improves their vision in dim light. Megabats use an enhanced sense of smell known as stereo olfaction. They use surrounding odors to detect food, shelter, and mates. Studies have shown that there is a relationship between bat nasal morphology, and their foraging patterns (Brokaw 2020).

Samoan flying fox (Pteropus Samoensis)

Muscles

Bat wings contain the same muscles as humans do in their arm but lack the fat. They have small specialized muscles that allow them to fly quickly, despite extreme temperature changes (Frederick 2019). These unique muscles are embedded in the wing membrane and are called plagiopatagiales. The plagiopatagiales work together in a network that allow bats to fly in gliding manner rather than a flapping manner. Studies have shown that bat plagiopatagiales work by adjusting skin stiffness in the wing. "Muscle activation and relaxation follows a distinct pattern during flight: They tense on the downstroke and relax on the upstroke (Orenstein 2014)."

Plagiopatagiales muscles

Reproduction

Most bats mate during the fall and give birth in the spring. This specific timing of the reproduction is crucial due to specific environmental conditions. In the spring, food sources are more abundant and bats are better able to care for themselves and their offspring. Due to their small size, bats are usually only able to carry one or two babies at a time. Reproductive strategies vary between bat species. For example, some female bats have delayed fertilization in which they store sperm in their uterus and fertilization doesn't occur until months after they mated. Another strategy of some species is delayed implementation, which is when a fertilized egg becomes inactive by going through multiple cell divisions and prevents implementation. The egg can become implanted after hibernation. A third strategy is sperm storage where "sperm is stored in either the caudal part of the epididymis or the vas deferens of the male or after copulation in the uterus and oviduct of the female (Bradley)."

Navigation

Although not fully understood yet, studies have been made about brain mechanisms that allow bats to uniquely navigate. These different mechanisms collect sensory information from the environment and allow bats to adjust and switch between navigational strategies. The selection method of bat navigation strategy is still under study.

Beaconing, path integration, and route-following are some of the different strategies that bats use. Beaconing is when a bat can directly sense its destination from point A to B. Beaconing can be based off visual or sound cues depending on the species and environment. Path integration is when a bat is calculates its location and direction in the absence of any external landmarks, solely based on the integration of self-motion information (Yovel & Ulanvosky 2017). Route-following is when a bat is able to recognize certain external landmarks that assist in creating a path for its destination.

Bat navigation strategies

Excretion

Bat feces, also known as guano are ecologically and culturally important. All around the world guano is used as fertilizer since it contains high levels of phosphate, nitrogen, and potassium. Guano is effective in Agriculture because it promotes rapid plant growth and fights off soil and fungal diseases. Guano is ecologically important because it disperses those important nutrients. Since bats are known to roost, or congregate in large groups, guano accumulates quickly and can alter the structure of a cave.

Other

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