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Underground Animals: Cool Cave Critters, Part One

Cave animals just might be some of the strangest animals on Earth. Adapted to living somewhere with little to no light and practically no vegetation, these animals have evolved to survive in extreme environments and the results are often unbelievable. A troglobite is an animal that exclusively live in caves and has adapted to its dark surroundings. Most troglobites cannot survive outside of the cave environment. Interestingly, while they never leave the cave environments, their lives are dependent on the world outside of the cave. Roots growing from plants above the surface, streams flowing from outside the cave and trogloxenes, and animals that use caves for shelter but travel outside the cave for nourishment are the only things that make life inside of caves possible. Roots allow nutrients to drip into the caves, streams bring in fresh food and dead animals and trogloxenes provide nutrient-rich feces and corpses that feed bacteria, insects and fungi that serve as the base of the cave’s food chain.

Because caves provide such a stable environment, many troglobites have lost the ability to adapt to temperature and humidity changes, which means most of these animals can only live in specific parts of their caves and many of them are endangered because they cannot branch out of their territory. Most troglobites survive in caves with humidity levels between 95 to 100 percent, but those that live in tropical areas deal with higher temperatures that result in more evaporation, thus, lower humidity levels. There are currently 7,700 known species of trilobites, but because scientists estimate that 90% of caves are still undiscovered due to a lack of visible entrances, many animals living in caves have yet to be discovered. Just recently, scientists discovered 225 new caves and 30 new species in Sequoia and Kings Canyon National Parks in California. Because there are so many cool cave animals, this article is really long, resulting in a two part series. This is part one, so if you’re hunting for part two, you can find it on my blog, Rue The Day. Images via Arne Hodalic [Wikipedia] and pfulton [Flickr]

Bats

While they may not spend their entire lives in caves, bats are one of the most important supporters of cave ecosystems. Their feces, dropped food and dead bodies provide food for insects, bacteria and fungi that support the carnivores in the cave. In some caves, the bat droppings pile up as high as one hundred feet. The guano is incredibly nutritious, making it a good cornerstone of any cave diet. In fact, a quarter-pound of it has more nutrients and protein than a Big Mac. Bats are the only mammals in the world that can fly, but there are so many types that they actually represent twenty percent of all mammal species. Their ability to fly has enabled them to become some of the most widely distributed mammal groups in the world. They live everywhere on earth except a few isolated islands, the Arctic and the Antarctic. While the stereotypes says all bats are blind, none are actually blind. Their small, underdeveloped eyes provide enough visual cues to help the bats navigate their routes beyond the area their echolocation can reach. Some species can even see ultraviolet light.

If you don’t like bats, consider the fact that humans might not exist without their help. Seventy percent of bats are insectivores and without them, the world could be overtaken with insects and our crops would quickly be eaten by bugs. Most other bats survive on fruit and nectar and there are many plants, particularly in tropical areas, that could not survive without the pollination and seed transportation of bats. Unfortunately, bats of the US are at serious risk right now thanks to the recent spread of the deadly white nose syndrome. This is a deadly fungus that grows on the noses of bats and has been known to kill more than 90% of certain colonies. It has so far been discovered in more than 115 caves and mines from Tennessee to Ontario and has killed millions of bats. Alan Hicks with the New York State Department of Environmental Conservation has described the impact as "the gravest threat to bats ... ever seen.” Image via HankPlank [Flickr]

Mexican Free-Tailed Bats

The Mexican Free-tailed bats are one of the most common mammal species in North America. They live in caves stretched out from the Southwest US all the way down to Argentina. In Austin, there is a colony of these bats that lives near the state capital during the summer months. With 1.5 million bats, it is the largest urban animal colony in the U.S. Each night, the bats eat between 10 and 30 thousand pounds of insects. In the winter, they have been known to live in colonies that have as many as 50 million individuals, meaning they have to start their nightly evacuation in the mid-afternoon to ensure everyone has a chance to get out by nightfall. The nursing roosts are so crowded that there are over 1500 babies per square foot.

Interestingly, the mothers only feed their own babies and they know exactly which is their own thanks to their baby's unique sounds and scents. The females conceive while hibernating as the males caress them. The sperm stays alive inside the female until she wakes up in spring and the egg is then released and fertilized.

Cave Nectar Bat

The cave nectar bat plays a huge role in the economies of the Southeast Asian countries in which they reside, as they are the only pollinator of the durian fruit, a crop that contributes $120 million to the economy every year. They are spread throughout Southeast Asia, inhabiting caves in India, China, Southeast Asia, Philippines, Sumatra, Java and Borneo. These bats spend the whole year inhabiting caves and live in small colonies, flying long distances each night to look for enough pollen and nectar to sustain them.

Ghost Bats

These bats are unique for being lighter colored than most species and having thin membrane on their wings that make them appear translucent and ghostly. Aside from these major differences, they also have no tails, large ears and very sharp teeth. The ghost bat is the only carnivorous bat in Australia, eating mostly insects, but also snacking on frogs, lizards, even other bats. Their colonies are usually fairly small, with fewer than one hundred individuals in each roost. Each female gives birth to only one baby each year. These bats are also fairly rare, as there are only about 5,000 in the wild.

Ozark Big-Eared Bats

True to its name, the Ozark Big-Eared Bats do have pretty massive ears, shooting about an inch above their heads.  They tend to live in limestone caves near oak-hickory forests and eat insects of all varieties, particularly enjoying moths. Their mating ritual is pretty cute and involves nuzzling heads. Interestingly, most mating occurs before hibernation in fall and the females hold on to the sperm. The egg isn’t fertilized until she wakes up in spring.

Vampire Bats

Vampire bats are one of the most famous bat species, but they are also some of the least common. It makes sense too. While blood is fairly easy to find, it is also incredibly low in energy. In fact, if they do not eat for two consecutive nights, they will die. To deal with this problem, the bats will help feed one another as needed. They even remember who fed them in the past and help these bats first. That’s not the only way bats are altruistic. They also are the only species of bat to adopt the babies of another bat if something happens to the mother. Vampire bats live in colonies of all kinds of sizes, but there is only one reproducing male in any colony and the rest are all females.

Contrary to popular belief, they don’t go around sucking on the necks of humans. Most vampire bats instead survive off of cows, goats, horses, tapirs and birds. When they drink blood, they don’t suck from their wounds either. Instead, vampire bats approach the animal from the ground, make a wound and then lick about two tablespoons of blood, which continues flowing due to an anti-coagulant found in their saliva. They do occasionally bite humans, but when they do, they generally nibble on the toe. Most people who have been bit don’t even realize it because the bites are painless. Unfortunately, the bats who bite humans are more likely to have rabies because these animals are unable to fly and are easily disoriented. Vampire bats are specially adapted to their lifestyle and they are even able to use their sense of hearing to detect whether or not a potential food source is asleep. Image via WikedKentaur [Wikipedia]

Birds

Like bats, cave-dwelling birds aren’t troglobites, but they are still a critical part of the cave ecosystem providing food with their droppings and dead bodies. While there are more than a few birds that take residence in caves, most stay towards the entrances, making them less important to cave life and less interesting then the swiftlet. Image via YTK23 [Flickr]

Swiftlets

If you’re familiar with bird nest soup than you know a little about swiftlets already. These are the birds that provide the saliva-based nests  used in the Chinese delicacy, but they are far more interesting than being just a simple ingredient source. Swiftlets choose to live in caves and to deal with the dark environment, many species have adapted by using echolocation like bats. Their method of echolocation is different from the bats as it is actually audible to humans. They use two clicking noises separated by a slight pause.

When approaching the nests, they add in a regular bird call to help warn nearby birds of their approach so they will not collide with one another. The birds have much shorter legs than most species, which make them unable to perch, but allow them to cling to nearly vertical surfaces of their homes. The birds leave the cave during the day so they can forage for insects, but always return home by night. Most of the birds are monogamous and each take part in caring for the babies. The birds will make a nest from saliva and then the male will impress the female by doing aerial displays. Most of the birds will have no more than one or two eggs at a time.

While many scientists worried that that collecting their nests would put the animals at risk of population loss, a recent study showed that modern, competent techniques of nest collection can actually increase the bird’s population. Image via Lip Kee [Flickr]

Amphibians


Olms

The Olm is one of the weirdest and most famous cave animals around. It was also the first troglobite to be discovered way back in 1689. Heavy rains in Slovenia washed them to the surface, where people believed them to be baby dragons that lived below the earth’s surface. At over a foot long, it’s also the largest troglobite –many are tiny and under an inch long. One of their most unique traits is their bright red external gills. While many amphibians have these as juveniles, they generally lose them as they get older. The olm has lungs, but these are completely secondary to their gills. Unlike most amphibians, they are exclusively aquatic.

They also differ by having only three toes on their front legs and two on their back. Olms live in the waters of underground limestone caves that stretch from the western border of Italy through Slovenia, Croatia and Herzegovina. They survive by feeding on small crabs, snails and insects. They don’t chew their food, but instead swallow it whole using their tiny teeth as a sieve to keep the larger particles in their mouth. Because food can be scarce underground, the olms are great at storing nutrients in their liver, they can even reabsorb their own tissues in some cases and they can survive up to ten years without eating. The animals have an amazing lifespan and can live an average of seventy years, even up to a century.

The olms have regressed eyes (they’re born with them but their skin grows over them later) and their skin lacks pigmentation, which is why they have been nicknamed the “human fish.” The skin is also to sense light and maintains the ability to produce melanin, so they turn dark if they are exposed to light long enough. While they are blind, they can still perceive light and their other senses, particularly those involving smell and sound, are beefed up to compensate. Olms can sense very low quantities of organic compounds in water and can detect prey more efficiently by smell than other amphibians. They have a special sensory organ that allows them to register weak electric fields which they use to orient themselves.

There is only one subspecies of olm, the black olm that is native to only one small area in Slovenia that is smaller than 39 square miles. The black olm has fairly normal eyes although they are smaller than most amphibians. This indicates that the black olm started evolving later than their flesh-colored cousins. Slovenian culture reveres the olm and they even issued a coin featuring the animal before switching over to the Euro. Images via Arne Hodalic #1, #2 [Wikipedia]

Texas Blind Salamanders

While the Texas Blind Salamander resembles the olm, it is not directly related. They do have quite a few similarities though. The blind salamander has external gills and feeds on insects, shrimp and snails. It is much smaller than the olm, growing to only about 5 inches long. As the name implies, the salamander is native to Texas, specifically Hays County’s Edwards Aquifer, and they are very popular in the state. Image via SteveSims [Wikipedia]

There are plenty more crazy cave animals, but as you can tell, this article has gotten mighty long, so be sure to check out part two of the series over on my blog, Rue The Day. It covers a variety of other creatures including arachnids, insects, snakes, fish and more.

Sources: Wikipedia #1, #2, #3, #4, #5, #6, #7, #8, #9, #10, #11, National Geographic and The Book Of Animal Ignorance


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Tried Bird Nest soup last year from like http://www.geocities.jp/hongkong_bird_nest/index_e.htm . Tastes really good… yeah, I thought it was gross at first, but wow, you won’t regret it.
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