Dark Banquet - Bill Schutt [27]
Besides their actual ability to feed on blood, perhaps the most fascinating of all vampire bat adaptations is one that we observed only once in our colony of Diaemus.
In 1984, zoologist Gerry Wilkinson reported that vampire bats in the wild commonly share food by regurgitating blood. Wilkinson, who made his initial observations on Desmodus rotundus, determined that about 75 percent of the time blood sharing occurred between a mother and her dependent offspring (until about the age of one). In other instances, sharing took place between related or unrelated bats.
Gerry’s results indicated that there were several reasons why this behavior occurred. Blood sharing between mothers and newborn pups presumably transfers nutrients and bacteria to the infant’s digestive tract. In humans there are normally over two hundred species of bacteria living somewhere on or in our bodies (it’s rumored that in some college dorms this number can hit five million species). In any event, these essential microbes (termed bacterial flora) are vital components of several physiological processes, most notably digestion.
In that regard, the mammalian small and large intestines (the terms refer to diameter, not length) are home to billions of bacteria that have evolved a number of mutualistic relationships with their warm-blooded hosts. Often referred to as endosymbionts, these bacteria get food and a warm, moist environment in which to live. The mammals reap a number of benefits from the relationship, including the absorption of vitamins B12 and K, which are secreted by the bacteria as part of their day-to-day functioning.*37 Additionally, indigenous bacterial flora inhibit or kill nonindigenous forms, and they also prevent infection by stimulating the immune system to produce antibodies that can cross-react with potentially harmful nonindigenous bacteria, should they appear. In hooved mammals (i.e., ungulates), as well as wood munchers like termites, the presence of certain endosymbiotic bacteria enables their digestive tracts to break down cellulose—the structural protein that makes up the plant cell wall. These bacteria are the prime reason herbivorous creatures are able to digest plant structures like leaves, stems, and wood. Since we don’t have these specific endosymbionts, it’s also the main reason why this type of “fiber” goes through humans like the vegan version of Roto-Rooter. Young herbivores aren’t born with their bacterial flora either but instead obtain them from adults (like their mothers) through regurgitation or by consuming their feces (coprophagia). For this reason, termite “babies” denied their fecal formula are unable to digest wood and quickly starve to death.
Other related studies, by researchers such as Long Island University geneticist Ted Brummel, have shown that symbiotic bacteria increase the life span of fruit flies, even though the bacteria are apparently not involved in the digestion of plant matter.
Blood sharing between related and unrelated vampire bats also occurs on a reciprocal basis; that is, bats that were experimentally starved for one night before receiving blood from another nonrelated individual were more likely to donate blood to that individual when it was starved. This behavior is almost certainly related to the fact that the bats need to acquire a blood meal every night (and will starve to death in two or three days if they don’t obtain one). So, over the course of their long lives (up to twenty years), there will presumably be numerous opportunities to receive and share food. The implication here is that Desmodus can remember past donors and can also recognize cheaters—those individuals who try to beat the system by rarely