Rousettus are among the smallest of the Megachiroptera. They are unique among this suborder of Old World fruit bats, in that they roost primarily in caves rather in tall trees like bats of the genus Pteropus. They are unique in that they are the only Megachiroptera that uses echo location. The way that this species does this is in itself worthy of note, in that it is the only form of bat echo location that is audible to the human ear. That is because they do not make the high frequency calls that most bats do in the larynx. Instead, their echo location calls are made by suddenly releasing the tongue upward away from the floor of the mouth. The two edges of the tongue are released asynchronously. In other words, one edge is released with a very slight time delay from the other. In this way, double signals are produced. The second signal is produced approximately 30 ms after the first. Each individual signal lasts for a duration of only 1 to 5 ms. These signals produced in the floor of the mouth are intense wide-band signals with frequencies between ten and sixty kHz.
Signals from the lower end of this frequency range are perceived by the human ear as a staccato of harsh cracking sounds. Egyptian Fruit Bats use their echo location only when orientation by means of vision is not possible, such as on very dark nights or in caves. As long as the light level is adequate, they will emit no signals at all, or only very weak ones. This method of echo location has evolved entirely separately from the more commonly known echo location system found among the rest of the world’s echo locating bats.
Rousettus aegyptiacus is found in Southern, Western, and Eastern Africa, Egypt, the Middle East, and Cypress. There are three subspecies R. a. aegyptiacus, found in North Africa, Cypress and the Middle East; R. a. Leachi, from Eastern and Soutthern Africa; and R. a. Occidentalis, from Western Africa. However, they only occur where there are suitable caves for roosting and freedom from human disturbance.
This species is unique among bats of the Megachiroptera in choosing to roost in caves instead of forming the familiar ‘camps’ like those of the flying foxes. Some of the more noteworthy roosting caves of this species are found in such remote locations as on Mount Cameroon at elevations of 6400 feet or 2000 meters. In 1810, this species was found roosting in the passages of the pyramids at Giza. Other substantial roosts are found in the Nile Valley, as far north as the Mediterranean Sea. Aside from caves, other roost sites chosen by this species include dark ruins, deep cellars, Roman Aqueducts, and burial chambers in Egypt. They are known for roosting in very large colonies.
Wherever this species chooses to roost, they do so in large numbers. In fact, mass colonies of this species are among the largest animal groupings in the world. They prefer large caves, and usually roost on flat cave ceilings relatively close to the cave entrance. Egyptian Fruit Bats have a very unique way of roosting. These bats hang, tightly packed together in very close groups, with both sexes and ages mixed together. The larger the colony, the more they crowd together, and the more aggressive and quarrelsome they seem to the human observer. There is a constant din of their squabbling and fighting throughout the day. It would seem to the observer that they never sleep. These bats fight over roosting spots, females, and food. They do this with their wings half open, but with their mouths closed. It appears as though they are ‘boxing’ with each other with their wings. This fighting is symbolic, and is accompanied with loud screeching. As a rule, the bats rarely injure each other.
Although the full extent of the natural diet of this species is unknown, it is known that Rousettus feed upon a huge variety of fruits from tropical shrubs and trees, and are known to fly vast distances to find ripe fruit in season, particularly ripe figs.
The females usually give birth to a single young at a time. On rare occasions though, twin births occur. The breeding season of this species is probably between December and March in most areas, and is thought to be governed by the food supply of the parents.
Widening of the birth canal is the first visible sign of an impending birth. Unlike most bat species, which hang by the thumbs as well as their feet while giving birth, the mother usually hangs in her normal roosting position, but with her wings open slightly. The baby’s head soon becomes visible at the opening of the birth canal.
After a few turning movements, the baby’s head is free of the birth canal, and then tips forward. The head is soon followed by the wings, and then the legs. Labour is apparent throughout the birth. Sometimes, the newborn is suspended entirely by the umbilical cord for a few moments before clinging to the abdomen of the mother. It is at this time that the newborn instinctively finds its mother’s teat, and immediately attaches itself with its deciduous (baby) teeth.
On average, a given birth takes several minutes. In the case of twins, the second baby can be born as much as an hour later. Often shorty after birth, the newborn emits shrill chirping sounds. The afterbirth can emerge as much as an hour after the baby is born. The mother consumes most of it, and as with most mammilian species this encourages lactation.
Most of our newborn Egyptian Fruit Bats on average weigh 0.8 ounces (22 grams). By comparison, the mother weighs in at about 4 and half ounces (127 grams). The offspring is protected from disturbance by other bats within the colony by the mother by surrounding it with her wings and completely covering it. Usually the young bat’s head can be seen resting in the bend of the mother’s wrist. Within only a few days after birth, the baby opens it's eyes and begins to take it's first steps. These are done without letting go of its mother’s teat. The baby attempts to get a foothold on the roost with its claws, while remaining next to the mother.
At birth the ears are floppy and folded, but by the 12th day they are held up in an adult manner and the baby responds to sound. The attentive mother grooms her offspring on a frequent basis by licking it. By two weeks of age, the young bat starts to swing from it's mother’s abdomen, with its wings spread in practice flight. By the third week of age, the wings are able to be fully extended, and the young begins exploring its immediate surroundings. It regularly chirps to keep it's mother informed of it's whereabouts. The mother responds in kind, and this duet continues until the mother and offspring are reunited.
Due to a loss of habitat from a combination of agricultural development and the effects of political instability, the Egyptian Fruit Bat, as well as most of the bats of the genus pteropus; are facing increasing threats to their continued existance in nature. It is important to remember that 70% of all of the World's fruit is pollinated solely by bats.
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