Hawaiian Hoary Bat - Ope’ape’a
This Article by Vanessa Parker-Geisman
The Hawaiian hoary bat (Lasiurus cinereus semotus) (or Ope’ape’a in Hawaiian) is a subspecies of the hoary bat found throughout the Americas (Lasiurus cinereus). The Hawaiian hoary bat is Hawaii’s only endemic land mammal and is federally protected under the endangered species act. Little is known of this sub-species, and general knowledge of its behavior is derived mainly from studies of its continental relative, the hoary bat.
The Hawaiian hoary bat is thought to have evolved from individuals that arrived in the Hawaiian Islands anywhere from 10,000 to several million years ago. Completing the 2,300 mile flight would require flight without rest for many days and unlike migratory species of birds, no known species of bat is known to travel such distances during any annual migration. It is thought that several individuals of the North American hoary bat were swept up by a storm traveling across the Pacific and thus arrived in the Hawaiian archiplelago. Regardless of how they arrived, their arrival was as an amazing feat.
The name ‘Hoary Bat’ refers to the bats coloration, a sometimes frosty reddish brown. The bat is a small insectivorous species weighing around 13-18 grams (about ½ an ounce) with a wing span of 13 inches (33 cm). Individuals mainly roost alone in trees and generally are thought to feed on moths and other species of insects available. The bat is documented to occur on all the Main Hawaiian Islands except Kahoolawe and Ni’ihau. It was first described as a sub-species in 1957 and listed as endangered in 1973 due to general concerns that the population was declining and lack of information regarding its ecology and behavior.
Although the Hawaiian Islands provide suitable climate year-round, these bats are thought to have maintained their continental relatives’ temporal habits. On the Big Island of Hawai’i, decreases in sightings of bats along coastal habitats from January through April are thought to indicate movement of bats to higher elevations on Mauna Kea and Mauna Loa, the islands two largest dormant volcanoes where they prefer the cooler temperatures. Both volcanoes have elevations of approximately 14,000 feet. At higher elevations the average daily temperature is colder and it is thought that the colder temperatures may allow them to achieve a lowered metabolic rate while resting.
Little is known of the reproductive patterns of this sub-species. It is thought that females may breed during late fall (October through November) and store sperm until the spring when they return to the warmer, coastal areas. This ability to store sperm through the winter has been documented with several other species of North American hibernating bats. Females give birth to a single offspring in a season. The young are born in summer (June through August) and stay with their mothers until they are fledged, which is thought to be a period of just a few months.
Due to their small size and solitary nature, discovery of these bats' roosts is rare and it is difficult to know current population size. Due to a lack of significant historical information concerning Hawaiian hoary bat populations it is difficult to know whether this species’ population has been significantly altered by the development of the Hawaiian Islands. It is easy to believe, though, that the loss of native forest in the past hundred years due to agricultural development has reduced the bat’s population.
Today studies regarding individual behavior and population status are underway, but much remains to be known about these bats before adequate protection for this subspecies can be ensured. Questions of the bats’ ecology remain to be answered including whether they prefer native species of tree to non-native species of trees for roosting, whether there are clear migratory patterns, and specifics regarding their diets.
While the Hawaiian Hoary Bat may have survived the journey from the Americas, it remains to be seen whether it will survive the impact of recent human development in Hawai’i.
Article by Vanessa Parker-Geisman
Vanessa has been working with researchers at the National Park Service on the Big Island of Hawaii to learn more about the Hawaiian Hoary Bats. Information found in this article is based on knowledge acquired in the field and from recent studies. For more information contact Vanessa Parker-Geisman.
The Hawaiian Islands are remote, geologically young and climatically varied. This is a fascinating place to examine island biodiversity. But hunt among the happy face spiders, swim along with the humuhumunukunukuapua’a, fly with the nene, and you will find that these islands contain only two native species of mammals. Since one is the monk seal that leaves only one native land mammal in Hawaii and it is the Hawaiian hoary bat (Lasiurus cinereus semotus, Ope’ape’a in Hawaiian).
Unfortunately there is no fossil record of the Hawaiian hoary bat. In fact, there are very few fossil records of bats in general. The earliest unearthed fossil (60 million years old – Eocene period) shows a fully developed bat (Pye 1999). There is no fossil record of pre-bat species and therefore only speculation as to how they evolved and when. "… it is clearly a fully formed bat and, despite its antiquity, does not serve as a ‘missing link’ between the bats and some older group." (Yalden and Morris 1975) Study of fossil brain capacities suggests that the hearing centers of their brains were as greatly enlarged then as they are today. This suggests strongly that prehistoric bats used echolocation just as modern-day bats do. There is other skeletal evidence that suggests that diet and behavior was much as it is today. What we do know is that their order, chiroptera (from Greek; "cheiros" meaning "hand" and "pteros" meaning "wing"), broke off from the rest of us mammals well over 60 million years ago.
So what do we know about the more recent origins of this endemic Hawaiian species? Since it inhabited the islands before humans arrived (about 1700 years ago) we will probably never know its whole story or the timing of its arrival. It is, however, very likely that it came to the islands by chance – via circumstances that biologists refer to as a "sweepstakes." Maybe it blew over thousands of miles of desolate Pacific Ocean on a powerful storm. Perhaps some were living in a tree that made its way from the mainland to the islands.
It is important to note that the Hawaiian islands were never part of a larger landmass. They are mid-Pacific volcanoes born of themselves and destined to recede back into the lonely depths. Kauai, the oldest of the main islands, is only about five million years old and the youngest (and largest) is Hawaii clocking in at only about a million years. Therefore it is not possible that this bat is any sort of habitat relic like those that inhabit an island that separated from a mainland, or even Gondwanaland or Pangaea. The best it could have done is to jump from one island to the next as they were formed and vegetated (if they arrived before the completion of these eight major islands).
Though the species Lasiurus cinereus semotus is found only in Hawaii, the family to which it belongs, Vespertilionidae, is truly cosmopolitan. Members of this not-so-elite group can be found on all continents except Antarctica and on islands around the globe. The range of its habitats is comparable to two other infamous mammals; humans and rodents. But the eurotopic adaptation of flight has allowed bats to colonize areas long before those other earth-bound species could reach those same areas. Examining the disharmonic distributions of organisms on many islands and frequently finding bats present shows just how capable these creatures are at colonizing new and distant areas.
The Hawaiian hoary bat (Lasiurus cinereus semotus) occurs only in the Hawaiian Islands.
And though flight is important it is not the only trait that gives bats an evolutionary advantage. Through adaptive radiation bats have achieved fascinating techniques for eating, sleeping, reproducing, etc. The best known of these is probably the use of echolocation. Bats have a variety of sight capabilities. Some have excellent vision while many rely more heavily on their sonar. Bats that use this sort of echolocation usually do it ultrasonically (above humans’ ability to hear) because they get a clearer "picture" of their surroundings that way. Look at a bat. Does it have big ears? If it does, that suggests that it relies heavily upon echolocation. The especially big ears are often used by bats that hover in place to pick off insects that crawl around on trees or on the ground. This is the case with the Hawaiian hoary bat. Many bats have oddly shaped faces. This is because some bats produce their echolocating sounds through their highly evolved noses rather than their mouths. Our Lasiurus cinereus semotus however, produces sounds from its mouth and vocal areas.
Varied diets have allowed bats to thrive and survive once they reach new lands. There is even evidence of coevolution between bats and pollinating plants. For example, the durian fruit is very popular in Malaysia. Twenty years ago it was discovered, after a massive die-off of the fruit trees, that they were pollinated by nearby cave-dwelling bats. Quarrying was threatening to wipe them out and, consequently, the durian trees as well. Fear of the loss of the fruit led to the suppression of the quarrying in that area. (Pye 1999)
Though most of the larger bats are frugivorous (fruit eaters) many small bats are carnivorous in a variety of ways. Some hunt by flying among their prey while others, like those mentioned above, hover near trees or other surfaces and pick off creepy crawly bugs. These latter types, the Hawaiian hoary bat included, are referred to as gleaners. Those that swoop are most likely insectivorous, but some species eat fish or frogs or even other bats. The Phyllostomus hastatus of Trinidad is omnivorous and enjoys fruit, insects, and even vertebrate prey when it can get its feet on them. Then, of course, are the three species of vampire bats. They live on the fresh blood of larger mammals. With their sharp incisors they bite or scrape the skin until the blood flows. They produce an anticoagulant to stop the blood from clotting and must often feed for an extended period of time. This is because blood is a relatively diluted food and it takes large amounts to get the nutrition that the bats need. Vampire bats’ stomachs and kidneys rapidly separate the water from the rest of the blood. In doing so, these bats can become engorged and unable to fly. After feeding they often hop away! Because of their peculiar feeding habits vampire bats can be carriers of blood-borne diseases, especially rabies. This can be passed on to other animals, livestock, or even humans. But these bats rarely attack humans and they don’t live in the San Francisco Bay area so please don’t allow this to prejudice you against the other 800 species of bats.
But, like so many other species, bats all around the world are threatened or endangered, so what’s being done to save them? In many parts of the world there is still great prejudice toward bats. This attitude is so unfortunate not only for bats but for people as well. Bats are great pollinators and eaters of insects that we consider pests, yet their habitats are still being purposely destroyed. Since they roost in such dense numbers (Bracken Cave near San Antonio is home on any given night to over 20 million bats) it is easy to do a lot of damage with relative ease. After Mexican freetail bats took roost under the renovated Congress Avenue Bridge in Austin, Texas, people began signing petitions to have them exterminated. (Tuttle 1995) Didn’t those silly Texans realize that one shouldn’t mess with an animal that is not only harmless but is greatly beneficial? They realize it now. It’s estimated that this particular colony eats more than 27,000 pounds of insects on an average night. Now Austin has dubbed itself the "Bat Capital of America" and the bats are a popular tourist attraction. In fact, the Texas Department of Transportation now purposely builds bat-friendly bridges. Structural engineer Mark J. Bloschock said that, "We have about six million bats already living in 59 Texas bridges and we’ll be building 15 to 20 new bridges a year that together will accommodate a million new bats."
Some farmers are now building "bat boxes" to house the animals and thereby cutting down on pesticide use. People like Bat Conservation International founder Berlin D. Tuttle work tirelessly to promote bat education and appreciation.
Much more can be learned about the Hawaiian hoary bat and about bats in general by visiting the Bat Conservation International web page at http://www.batcon.org/
Article by Andrew Bley