DNA from Feces Reveals that Vampire Bats Thirst for Pork Most

It’s hard to tell who vampire bats like to feed on just by looking at their feces since they dine exclusively on blood. But now, researchers analyzing DNA isolated from bat droppings reveal that they crave pigs’ blood most, though they’ll settle for chicken blood, according to a new Journal of Mammalogy study.

When trying to identify a forager’s prey preference, you usually inspect their feces for fur, undigested bits, or bone fragments from their meals. To see whose blood is being sucked by common vampire bats (Desmodus rotundus), a trio led by Paulo Bobrowiec from the Instituto Nacional de Pesquisas da AmazĂ´nia examined the DNA from fecal samples. They fed eight captive bats blood from chickens, cows, pigs, dogs, and humans—the most frequently attacked prey items during the night in rural areas of the Brazilian Amazonia. The blood was collected from slaughterhouses (cows, pigs) and anesthetized dogs at a vet clinic, and people blood came from a local hematology center; the chickens were provided live within the bat enclosures. The team extracted and amplified DNA from blood samples of each prey species and from 190 fecal samples from these bats (that’s 38 samples of each prey species).
Additionally, the team also captured 157 Desmodus rotundus bats and collected 88 fecal samples from 18 small villages along a lake and two rivers in central-western Brazilian Amazonia. They also measured the availability of domestic animals. No traces of wild, rainforest vertebrates (like deer or tapirs) were identified in the fecal samples—which suggests that they selectively feed on domesticated animals. After all, livestock is more predictable, detectable, and accessible.

Chickens, they found, were the most attacked prey species, making up 61.4 percent of the identifiable samples—but fowl is only exploited as a secondary, complementary food source. When available, pigs were the highly preferred prey. Preference is a measure of the proportion of attacked prey and the proportion of available prey species: The one attacked more than expected by chance is the one that’s preferred. According to Science, the bats were seven times more likely to feed on pigs than chance would predict.

It’s likely that the bats’ thirst for pigs’ blood is related to its higher nutritional value compared with other farm animals, as well as the nighttime corralling of pigs (as opposed to horses and cows who might be allowed to roam free). Furthermore, Desmodus saliva liquefies mammal blood more readily than it does avian blood—making it easier and faster to ingest.

Vampire Bats Make Friends By Sharing Blood
They may be blood-thirsty creatures of the night, but vampire bats are also surprisingly altruistic and sociable, as new research into their food-sharing habits suggests. The study, which appeared today in Proceedings of the Royal Society B, sheds new light on the generosity of these flying mammals, indicating how sharing their crimson sustenance helps to foster key social relationships.

The fact that vampire bats regurgitate blood in order to feed those who have been unsuccessful in their nightly hunt is not new information. However, until now, researchers had struggled to understand why some females share their food with bats who are not part of their own kin group.

In order to solve this puzzle, a team of biologists at the Smithsonian Tropical Research Institute in Panama conducted a series of experiments that enabled them to observe the bats’ sharing patterns more closely. This involved starving certain bats for periods of 24 hours, before reintroducing them into their social groups and noting which members did and didn’t offer them food.

As it turns out, bats tend to share with others who have previously shared with them in their times of need, and will often shun those who have displayed stinginess in the past – regardless of whether or not these bats are part of their own kin group. Interpreting these results, the study authors conclude that this practice plays a vital role in the creation of social networks, which ultimately benefit the individual as well as the group.

“Non-kin sharing widens social network size not merely by increasing groupmate survival, but by creating or strengthening social ties that yield reciprocal returns,” the study claims. “As a consequence, individuals that feed more non-kin should have more donors when the need arises.”

Nurturing these social relationships is vitally important to vampire bats, since they can easily starve if they go more than a couple of days without securing a meal of their own. As a result, the bats in the study displayed a propensity to strengthen as many of these non-kin bonds as possible, thereby increasing their number of potential donors.

This information will no doubt cause many to view vampire bats in a different light, as it shows a nicer, more vulnerable side. Of course, others will insist on shattering this image by pointing out that the creatures are equipped with infrared sensors that enable them to home in on their prey’s veins, and that their thirst for blood has caused them to lose the ability to taste other things.

The Mammals of Texas - Online Edition
Hairy-legged Vampire Order Chiroptera : Family Phyllostomidae : Diphylla ecaudata Spix

Description. A relatively large, sooty-brown bat with no tail; a narrow, hairy interfemoral membrane; short, rounded ears; and a short, pug-nosed snout. The dentition is highly modified with the middle upper incisors larger than the canines; the outer incisors very small and set so close to the canines that they are easily overlooked; the crowns of the outer lower incisors seven-lobed, fan-shaped, and more than twice as wide as the inner lower incisors; premolars and molars very small and probably non-functional. Dental formula: I 2/2, C 1/1, Pm 1/2, M 2/2 X 2 = 26. External measurements average: total length, 85 mm; foot, 13 mm; forearm, 53 mm. Weight, 30-40 g.

Distribution in Texas. From southern Texas southward to eastern Peru and Brazil. Known from Texas on the basis of one female taken May 24, 1967 from an abandoned railroad tunnel 19 km west of Comstock, Val Verde County.

Habits. This bat is primarily an inhabitant of tropical and subtropical forestlands. Its daytime retreat is normally a cave which it may share with other species of bats, but it has also been found roosting in mine tunnels and hollow trees. In the Mexican state of San Luis Potosi, Walter Dalquest found that these vampires were more solitary than the common vampire (Desmodus), and they did not gather in groups, even when several individuals inhabited a cave. Consequently, pools of digested blood do not form and there is only a slight odor of ammonia in the caves they inhabit. He found about 35 individuals, mostly females with young, in one cave but usually only one, two, or three were present in a given cave. These bats are shy, quick of movement, and readily take flight when molested.

The food of Diphylla is the blood of warm-blooded vertebrates, mainly birds, including domestic chickens. Ernest Walker reported that Diphylla attacks the legs and cloacal region of chickens. One bat was "observed alighting on the tail of a chicken, hanging by its hind legs and biting the exposed skin in the cloacal region, and then lapping up the blood while in an upright position."

This species seems to be reproductively active throughout the year. Pregnant females have been reported from Mexico and Central America in March, July, August, October, and November. The number of embryos per female is normally one, but one female captured July 8 in Chiapas, Mexico, contained two nearly full-term (crown-rump length 34 mm) embryos. The reproductive condition of the female captured in Texas was not recorded.

Although only one specimen of the hairy-legged vampire is known from Texas, it is possible that a thorough search of the caves in the Hill Country and along the Rio Grande will reveal additional records of this species or the common vampire (Desmodus rotundus) which have been taken in northern Mexico no more than 200 km from the Texas border. Since Diphylla is a possible reservoir of bovine paralytic rabies, it is of economic importance to the cattlemen and sportsmen of Texas.

Photo credit: Merlin D. Tuttle, Bat Conservation International.


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BATS. Megabats, Flying-foxes, Fruit bats and Microbats: DNA from Feces Reveals that Vampire Bats Thirst for Pork Most
DNA from Feces Reveals that Vampire Bats Thirst for Pork Most
DNA from Feces Reveals that Vampire Bats Thirst for Pork Most
BATS. Megabats, Flying-foxes, Fruit bats and Microbats
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