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Vultures evolved extreme gut to handle disgusting food, scientists say

Nov. 25, 2014
Courtesy of the University of Copenhagen
and World Science staff

Some ex­treme adapta­t­ions—in­clud­ing very strong stom­ach acid—help vul­tures live on rot­ting, often poop-con­tam­i­nated meat that would poi­son or kill most oth­er an­i­mals, a study has found.

When vul­tures eat lunch they happily strip rot­ting car­casses to the bone. If a hide is too tough to bite through, they don’t hes­i­tate to en­ter a car­cass us­ing oth­er routes, in­clud­ing the back en­trance—the anus. What in­gre­di­ent this adds to the feast is not hard to see.

A turkey vulture eats a dead gull at Mor­ro Bay, Calif. (Cour­tesy Ke­vin Cole, CC BY 2.0)


Yet the birds are ap­par­ently im­mune to the re­sult­ing cock­tail of deadly mi­crobes in their din­ner such as Clos­trid­ia, Fuso- and Anthrax-bac­te­ria.

“To in­ves­t­i­gate vul­tures’ abil­ity to sur­vive eat­ing this pu­trid cock­tail, we gen­er­at­ed DNA pro­files from the com­mun­ity of bac­te­ria liv­ing on the face and gut of 50 vul­tures from the U.S.A.,” said re­search­er Lars Hes­t­b­jerg Han­sen of Aar­hus Uni­vers­ity in Den­mark.

“Our find­ings en­a­ble us to re­con­struct both the si­m­i­lar­i­ties, and dif­fer­ences, be­tween the bac­te­ria found in tur­key vul­tures and black vul­tures, dis­trib­ut­ed widely in the West­ern Hemi­sphere.” 

On av­er­age, the re­search­ers found vul­tures’ fa­cial skin con­tained DNA from 528 dif­fer­ent types of mi­croor­gan­isms, but the gut re­vealed DNA from only 76 types. A lot of them are get­ting killed on the way down, said Roggen­buck and col­leagues, whose find­ings are pub­lished in the jour­nal Na­ture Com­mu­nica­t­ions.

“There has been strong adapta­t­ion in vul­tures when it comes to deal­ing with the tox­ic bac­te­ria they di­gest. On one hand vul­tures have de­vel­oped an ex­tremely tough di­gestive sys­tem, which simply acts to de­stroy the ma­jor­ity of the dan­ger­ous bac­te­ria they in­gest,” he ex­plained.

“On the oth­er hand, vul­tures al­so ap­pear to have de­vel­oped a tol­er­ance to­wards some of the deadly bac­te­ri­a—species that would kill oth­er an­i­mals ac­tively seem to flour­ish in the vul­ture low­er in­tes­tine.”

These ob­serva­t­ions, the re­search­ers said, raise the ques­tion of wheth­er the Clos­trid­ia and Fusobac­te­ria in the gut simply outcompete the oth­er bac­te­ria without ben­e­fit­ting the bird, or in con­trast, if their pres­ence ac­tu­ally con­fers di­e­tary ad­van­tages for the vul­tures. The re­sults, they say, sug­gest it’s probably a bit of both­—the sur­viv­ing bac­te­ria probably out­com­pete the oth­er mi­crobes, but al­so pro­vide the birds with im­por­tant nu­tri­ents by help­ing to break down the car­ri­on.

The uni­verse of mi­crobes with­in the avi­an gut is not well un­der­stood but “it is not un­rea­son­a­ble to sup­pose that the rela­t­ion­ship be­tween birds and their mi­crobes has been as im­por­tant in avi­an ev­o­lu­tion as the de­vel­op­ment of pow­ered flight and song,” said Gary Graves of the Smith­so­nian In­sti­tu­tion’s Na­t­ional Mu­se­um of Nat­u­ral His­to­ry in Wash­ing­ton, who par­ti­ci­pated in the work.


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Some extreme adaptations—including very strong stomach acid—help vultures thrive on rotting, poop-contaminated meat that would severely poison or kill most other animals, a study has found. When vultures eat lunch they happily strip rotting carcasses to the bone. If a hide is too tough to bite through, they don’t hesitate to enter a carcass using other routes, including the back entrance—the anus. What ingredient this adds to the feast is not hard to see. Yet the birds are apparently immune to the resulting cocktail of deadly microbes in their dinner such as Clostridia, Fuso- and Anthrax-bacteria. “To investigate vultures’ ability to survive eating this putrid cocktail, we generated DNA profiles from the community of bacteria living on the face and gut of 50 vultures from the U.S.A.,” said researcher Lars Hestbjerg Hansen of Aarhus University in Denmark, who with doctoral student Michael Roggenbuck lead the study while at the University of Copenhagen. “Our findings enable us to reconstruct both the similarities, and differences, between the bacteria found in turkey vultures and black vultures, distributed widely in the Western Hemisphere.” On average, the researchers found vultures’ facial skin contained DNA from 528 different types of microorganisms, but the gut revealed DNA from only 76 types. A lot of them are getting killed on the way down, said Roggenbuck and colleagues, whose findings are published in the journal Nature Communications. “There has been strong adaptation in vultures when it comes to dealing with the toxic bacteria they digest. On one hand vultures have developed an extremely tough digestive system, which simply acts to destroy the majority of the dangerous bacteria they ingest,” he explained. “On the other hand, vultures also appear to have developed a tolerance towards some of the deadly bacteria—species that would kill other animals actively seem to flourish in the vulture lower intestine.” These observations, the researchers said, raise the question of whether the Clostridia and Fusobacteria in the gut simply out-compete the other bacteria but don’t confer any benefit to the vulture, or in contrast, if their presence actually confers dietary advantages for the vultures. The results, they say, suggest it’s probably a bit of both—the surviving bacteria probably outcompete the other microbes, but also provide the vultures with important nutrients by helping to break down the carrion. The universe of microbes within the avian gut is not well-understood but “it is not unreasonable to suppose that the relationship between birds and their microbes has been as important in avian evolution as the development of powered flight and song,” said Gary Graves of the Smithsonian Institution’s National Museum of Natural History in Washington, who participated in the work.