Stolen: The unique physiology of bats
special to the daily
Bats are amazingly well-adapted to the environment they live in and are unique among mammals in many ways.
Bats have an acute sense of smell and hearing. Although the eyes of most microbat species are poorly developed, vision is used to navigate for long distances when echolocation is not useful. Some species are even able to detect ultraviolet light.
The finger bones of bats are much more flexible than those of other mammals because the cartilage in their fingers lacks calcium and other minerals nearer the tips. The cross-section of the finger bone is also flattened compared to the circular cross section of a human finger making them especially flexible. The skin on their wing membranes is very elastic and is very stretchable.
The wings of bats are much thinner than those of birds, so bats can maneuver more quickly and more accurately than birds, but are also delicate and can rip easily. Luckily the tissue is able to regenerate, and small tears can heal quickly.
The surface of their wings is equipped with touch-sensitive receptors which are a bump with a tiny hair in the center allowing the bat to detect and collect information about the air flowing over its wings. The sensors provide feedback to the bat to change the shape of its wing to fly more efficiently.
Another kind of receptor cell is found in the wing membrane of species that use their wings to catch prey. These receptor cells control the stretching of the membrane, and are concentrated in areas of the membrane where insects hit the wings where the bats capture them.
Bats often are highly gregarious and form large breeding colonies. Male bats give out special calls to let the females know where they are. Mating often includes soft chattering and licking. A single male may mate with 30 or more females.
Female bats use a variety of strategies to control the timing of pregnancy and the birth of young, to make delivery coincide with maximum food ability and other ecological factors.
Females of some species have delayed fertilization, in which sperm are stored in the reproductive tract for several months after mating.
Other species exhibit delayed implantation, in which the egg is fertilized after mating, but remains free in the reproductive tract until external conditions become favorable for giving birth and caring for the offspring.
In some species, fertilization and implantation both occur but development of the fetus is delayed until favorable conditions prevail.
All of these adaptations are designed so that the pup is born during a time of high local production of fruit or insects.
Giving birth itself is a precarious process. The mothers of many species hang inverted, grabbing the newborn as it emerges from the birth canal and the newborn grabs the abdominal fur of the mother with its hind feet. Other species of bats hang by their thumbs, and cradle the emerging young in their tails and swinging them into a membrane which stretches between their legs. There have been reports of females helping others with the birth of young.
Pups usually begin nursing almost immediately after birth. Mothers of some species carry their suckling newborn young on feeding trips, but the young rapidly grow, and get too heavy, so mothers leave them behind while foraging. They find their own youngster in a mass of others on return to the maternity roost by smell and it’s unique squeak.
The offspring of some tree-roosting bats in Colorado, such as the red bat and the hoary bat, lead a much more solitary life. Young are moved from roost to roost by their mothers even when they are quite large. During these shuttle flights, mothers may carry a youngster more than half their body weight. The young, having reached a certain size are typically left in safe havens while the mother forages.
At birth the wings are too small to be used for flight and it takes six to eight weeks before they can fly on their own.
Mortality of young bats is very high during this developmental stage because carnivores such as skunks, raccoons, coyotes. domestic cats and dogs kill juveniles. In addition, predators such as snakes, hawks and owls have been observed grabbing bats as they exit a roost.
Only about half the young born each year survive to adulthood. A single bat can live over 20 years, but the bat population growth is limited by the slow birth rate.
Because of their many unique characteristics: longevity, disease resistance, ability to become torpid easily and their sonar capabilities, they have been useful in the study of many disciplines of science. For example, because some bat species seem to be resistant to rabies (they do not succumb to the virus), they are of interest to immunologists.
They have been used in variety of experiments in space biology because they can survive in extreme environments that are lethal to other animals. Little brown bats can survive temperature extremes of 21 degrees to 131 degrees F, and cave bats can tolerate extremely high levels of carbon dioxide.
The sonar capabilities of bats have been used as models in the development of navigational aids for the blind and for the development of aircraft radar systems.
Because the wing membranes of bats are nearly transparent, and blood vessels are highly visible, this has been helpful to researchers studying the effects of smoking and alcohol consumption, blood cell mechanics and tissue regeneration. In addition, bats are used in studies involving aging, contraception, artificial insemination, drug testing, vaccine development, low-temperature surgical techniques and speech pathology.
Breckenridge resident Dr. Joanne Stolen is retired from teaching microbiology at Rutgers University.
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