Bats

Chiroptera, commonly known as bats, are very curious animals. Having earned a bad name for being considered sinister creatures of the night, they have given rise to legends as famous as Dracula. Despite the fact that only three species feed on blood, they are often associated with vampire myths. However, in some regions like China, bats are a symbol of profit and happiness. Although the fame of these animals is not usually very good, It is important to know that they are vital in ecosystems: They pollinate, control insect pests, and disperse plant seeds.

These animals belong to the placental mammals. Currently there are about 1100 species that represent 20% of all known mammal species. For this reason, they are the second order with the most diversity, after rodents. They inhabit all continents, except Antarctica. It should also be noted that bats They are the only mammals capable of flying. since its front legs are wings. However, the most notable feature of these animals is their ability to orient themselves and hunt by echolocation.

Description of bats

Birds, extinct pterosaurs, and bats are the only vertebrates that can fly. All bat fingers, with the exception of the thumb, are attached to a thin membrane of skin called the patagium. It is made up of two layers of skin with another layer between them with blood vessels, innervated tissues and muscle fibers.

Depending on the species, the fur of bats varies. They are generally grey, red, yellow, black or brown. Also its size depends on the type of bat. The blowfly bat is the smallest mammal today. It has a length of 29 to 33 millimeters and usually weighs about 2 grams. In contrast, the great Philippine flying fox can measure up to 1,5 meters long and weigh 1,2 kilos.

Another feature that makes these mammals unique is their hip joint, which is turned 90º. Thus, the legs are oriented to the sides and the knees almost backwards. Because of this, they have a rather clumsy gait. However, this feature allows them to fly better with the patagio and hang upside down. The toes of bats have a claw that they use to climb and hang. When they are hanging, their weight exerts a type of traction on their tendons. This traction is responsible for keeping the claws in the hooking position. Thanks to this mechanism they can remain hanging even when they are asleep. In this way they do not waste energy even if they remain in this position for a long time.

suborders

There are two large suborders belonging to bats: Microchiroptera and Megachiroptera. Despite what it may seem from the name, they are not differentiated by their size. There are microbats that are larger than some megabats. The main differences are the following:

• Megachiroptera are frugivorous, while most microchiroptera are insectivorous.
• The microbats use echolocation to orient themselves, the megabats use sight and smell, with the exception of one species.
• Megachiroptera have a claw on the second toe.
• The ears of microbats have separate edges at the base, the ears of megabats form a closed ring.

Echolocation

Echolocation is a perception system used by bats, dolphins and sperm whales. It is a system that produces echoes by emitting sounds. When the sound returns, the auditory nervous system transmits it to the brain. This helps these animals to detect obstacles, to orient themselves, to find prey and to interact with others of their species. Echolocation is able to provide bats with the size, direction and speed of their prey.

Since echolocation analyzes echoes, bats have adaptations for both receiving signals and emitting them. These adaptations are found in the auditory system and in the larynx respectively.

Microbats contract the larynx to emit ultrasounds that vary in rhythm, frequency, intensity, and duration. The emission takes place through the nose or through the mouth and is subsequently amplified by means of "nasal blades". Each species emits different frequencies. The human ear is capable of perceiving up to 20 kHz. However, bats can emit from 15 to 200 kHz.

How do bats take advantage of it?

Thanks to the time difference between the emission of the sound and the reception of the echo, bats calculate the distance at which their prey is. To deduce the direction, they look at how long it takes for the echo to reach the right and left ears. Besides, the different species have an auricle adapted to their type of flight: the faster they are flying, the ears are shorter.

Although this system may seem very useful and accurate for finding your way around when there is little light or total darkness, echolocation also has its disadvantages compared to visual perception. Among them are the following:

• The energy cost for its production is very high.
• The perception of visual images is faster than the echo response.
• The sound field is limited compared to the visual field of other mammals.
• The range is also limited, usually less than 20 meters.
• The resolution of the type of image it produces is very low.

The life cycle of bats

Generally, bats They reach sexual maturity at twelve months of age. Species have different mating systems. While some are promiscuous and mate with various partners, others are monogamous. In this case, the male and the female live together with her offspring and between the two of them protect and feed them. Also behavior during courtship varies greatly between different species. For some bats it is a very complex task, while for others it is almost non-existent. It may even be the case that the males of some species mate with females while they are hibernating, so they hardly react to it.

Bats develop embryos in 3-6 months. Depending on the species, climate, and food availability, gestation time can last anywhere from forty days to ten months. In general, females have one pup, maximum two, per litter once a year. Some species, such as the reddish boreal bat, can give birth to up to three or four pups. To produce enough milk, mothers need a large energy intake. Newborns already have a weight that ranges from 10 to 30% of the mother's weight. The young are completely dependent, they need their mother to feed and protect them.

In temperate zones, bats form maternity colonies, you could say that these are nurseries. Thus, they reduce the energy expenditure and heat loss of each of the members. Young animals of small species are capable of flight at 20 days. Larger bats, on the other hand, can take up to three months to start their first flight.

reproductive physiologies

Several species of the Bats have evolved complex and different reproductive physiologies.

• Ovulation: It is common in bats that inhabit temperate zones. Their mating takes place in late autumn and the female stores the semen during the winter until ovulation occurs in spring. Thus, the young are born in summer.
• Deferred implementation: The embryo begins to develop, but this process stops shortly thereafter until conditions are favorable again. In addition, they can lengthen the gestation time until there is a better time with more food.

Longevity

On average, bats live between four and five years. However, they can reach between 10 and 24 years. There are even species that can reach 30 years of age. In general, the longevity of mammals is usually closely related to their size. Because of this, it is surprising that bats can reach such old ages. It is estimated that they live three and a half times longer than other mammals of similar size.

bat ecology

Bats are found in all habitats except the polar regions, the highest mountains, and the oceans. They usually live in underground corners like cracks and fissures in the walls and in the trees. They also inhabit human buildings such as basements, bridges or warehouses. The diet of these mammals is very varied. Most of them feed on insects, others on fruits and some are omnivorous. Most bats rest during the day and eat at night. Some species of bats are solitary, while others live in colonies that can be made up of up to 50 million individuals. These very large colonies consume between 45 and 250 tons of insects every night. Like most mammals, bats are viviparous.

Hibernation

When winter comes, many animals go into torpor. They do this not only because of the low temperatures, but also because of the scarcity of food. Most bats do not migrate, but rather hibernate until spring. During this state, bats they lower their body temperature and decrease their metabolic functions in order to prolong their energy reserves. No other mammal is capable of lowering its body temperature as much as bats, which can reach as low as -5ºC in some species.

Before the coldest time of the year begins, bats ingest huge amounts of food to accumulate reserves and not starve during hibernation. At this point, they wake up periodically to defecate and urinate or to change places. While some species wake up every ten days, others can be asleep for up to ninety days. Hibernating bats can also become torpid in summer, when the weather is cold or when there is a shortage of food. However, it is not as extreme as hibernation.

Predators

Generally, bats have very few natural predators. They are usually birds of prey, snakes and large lizards and some carnivorous mammals. However, some species introduced by humans can be fatal to bats. Cats are also very dangerous to bats. To protect themselves, some of these flying mammals fight or play dead.

In the tropics, snakes and boas they climb trees to capture flying foxes while they are resting. When their attacks are very repeated, they cause a significant impact on populations by leaving them without pups or young individuals. Snakes that hunt in caves, on the other hand, do not have bats as their usual food.

There are also several dangerous birds for bats. Among them is the common kestrel, the peregrine falcon and the European hawk. The bird of prey known as the bat kite specializes in hunting bats. However, nocturnal birds are the most dangerous for these flying mammals. Barn owls and owls may feed on them sporadically.

Among carnivorous mammals, few actively hunt bats. These include skunks, boreal raccoons, mustelids, and bobcats. Other predators such as the fox or the European badger feed only on pups that have fallen to the ground, but they are unusual prey. There are other species that eat bats from time to time, such as the field mouse, mygalomorphic spiders, the bullfrog and some carnivorous fish.

bat feeding

Bats have almost as varied feeding habits as all other mammals combined. Due to this dietary diversity there are so many morphological, ecological and physiological differences among the bat species. These animals eat insects, pollen, fruit, flowers, nectar, leaves, blood, carrion, mammals, reptiles, fish, birds, and amphibians. Some species are even omnivorous.

insectivores

The vast majority of bats are insectivores. As they are nocturnal hunters, they have no competition when it comes to feeding, since insectivorous birds are diurnal. Bats can feed on almost any type of insect. On some occasions they also hunt other types of arthropods, such as spiders, crustaceans, centipedes or scorpions.

Many of these bats They are small in size and capture their prey in flight. To do this, some use their legs or wings. Others are equipped with a membrane between their lower legs, called a uropatagium. In many cases it is shaped like a bag and with it they capture insects.

However, Not all bats hunt only in flight, but also on land. Some insectivorous bats, such as the Greater Horseshoe Bat, are capable of setting up ambushes, waiting in a fixed location to pursue their prey. Another species of bat, the Australian false vampire, attacks small vertebrates and large insects from above. After capturing them with his feet, he takes them to the top of a tree to eat them. It is a tactic similar to that of the birds of prey.

frugivores and polynivores

Among all bat species, about a quarter are vegetarian. These are found mainly in equatorial and tropical zones. They feed mainly on fruits, nectar and sometimes leaves. Some species supplement their diet with birds and carrion. They generally prefer sweet, fleshy fruits without much scent or flashy colors. Fruit bats use their teeth to tear off the fruit and consume it on some overhanging branch of the tree. When they have sated their appetite, they drop the rest of the fruit, including its seeds, which take root and eventually become new fruit trees. Currently there are more than 150 plants that depend on these animals to reproduce.

Approximately 5% of bats are polynivorous, that is, they feed on pollen. Species belonging to this group have atrophied jaws and masticatory muscles. Its long, pointed nose and raspy tongue serve to reach the pollen and nectar inside the flowers.

carnivores and piscivores

Today there are few species of bats that are considered strictly carnivorous. They are usually called this when their diet mainly involves small vertebrates, not counting fish. Among the foods of bats that consume only meat, are other bats, arthropods, birds, small rodents, frogs and lizards.

Some of these flying mammals feed mainly on fish, but as with carnivores, it is not usual for it to be their exclusive food. Piscivorous species usually have some special adaptations for fishing: Very elongated legs, a spur on its hind limbs, and claws. They are also equipped with a very sensitive echolocation system. They locate their prey through turbulence caused by schools of fish on the water surface. It should also be noted that there are some bats that feed on marine fish and crustaceans. Because of this, they have developed the ability to drink salt water. This characteristic is very unusual in mammals.

Hematophages

Despite the popular belief that bats feed exclusively on blood, it really there are only three species considered hematophagous. They all live in America and are known as vampires. Among its victims are cattle, toads, guanacos, tapirs, dogs and birds.

At dusk, vampire bats come out to search for their prey in groups of two to six individuals. When they locate the victim, usually a sleeping mammal, they land in an area close to the animal and approach it by land. They have a heat sensor in their nose that helps them find the right place to bite. They lick the blood and thanks to its saliva, which contains anticoagulants, bleeding is prolonged.

The victims of these animals lose little blood in this process, about 15 to 20 milliliters. However, wounds can become infected and bats can transmit parasites and viral diseases, like rage. Despite the fact that this zoonosis is much more frequent in other animals such as skunks or foxes, care must be taken when handling blood-sucking bats.