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Scavenger

Scavengers are animals that feed on dead and decaying organic matter. Often the term is used to describe the consumption of carrion, the bodies of animals that have died from causes other than predation or the bodies of animals that have been killed by other predators. However, the term is also used to describe animals that feed on rotting plant matter or refuse.

Etymology
Scavenger is an alteration of scavager, from Middle English skawager meaning "customs collector", from skawage meaning "customs", from Old North French escauwage meaning "inspection", from schauwer meaning "to inspect", of Germanic origin; akin to Old English scēawian and German schauen meaning "to look at", and modern English "show" (with semantic drift). == Related terminology ==
Related terminology
Animals that subsist entirely or mainly on decaying biomass (e.g. dead animals, dead plants) are called obligate scavengers, while those capable of obtaining food via other methods are termed facultative scavengers. Animals that rely specifically on carrion as a food source are called obligate necrophages. Animals that feed on particulate plant or animal matter (e.g. humus, marine snow) are typically categorized as detritivores rather than scavengers. The midge fly Propsilocerus akamusi, which feeds on detritus in the sediment of freshwater lakes, is an example of a detritivore. == Types of scavengers ==
Types of scavengers
Scavengers that feed on carrion s (Gyps fulvus) eating the carcass of a red deer in Spain Obligate scavenging of carrion (obligate necrophagy) is rare among vertebrates, due to the difficulty of finding enough carrion without expending too much energy. New World vultures such as the black vulture, and Old World vultures such as the griffon vulture, white-backed vulture and lappet-faced vulture, are examples of obligate carrion scavengers. Gulls, crows and magpies frequently scavenge roadkill. Other vertebrates, for example Egyptian mastigures, scavenge to survive during times of food scarcity. Aquatic and semi-aquatic vertebrates feed on carrion too. Carrion-eating scavengers found in marine settings include hagfish, great white sharks, northern wolffish and abyssal grenadiers, and carrion-eating scavengers found in freshwater settings include American alligators, Eurasian otters and common midwife toads. Other invertebrates, such as blow flies, flesh flies and yellowjackets, also feed on carrion but are not reliant on it for survival. Also, yellowjackets can hunt caterpillars and other insects and feed on nectar, sap and fruit. In addition to the terrestrial examples above, many aquatic invertebrates consume carrion. The common octopus, European green crab and seven-armed starfish are all marine invertebrates that feed on carrion, and the ribbon leech Erpobdella obscura and red swamp crayfish are freshwater invertebrates that feed on carrion. protect themselves from infection and intoxication (e.g. strong immune systems, toxin-resistant physiologies), gorge themselves when food is available (e.g. expandable intestines), and conserve energy between meals (e.g. gliding flight). Some stag beetles are obligate scavengers of dead plant material. For example, Lucanus cervus is dependent on dead wood during the larval stages of its life cycle. Adult Lucanus cervus beetles lay their eggs near the stumps of dead trees, and the larvae then spend the next 4 to 7 years feeding and growing in size. Types of wood eaten include oak, ash, elm, sycamore, lime and hornbeam. Darkling beetles (tenebrionids), woodlice, are also facultative scavengers of dead plant material. Scavengers that feed on discarded food scavenging in a garbage can for food In urban settings, some animals regularly explore public parks and garbage cans for discarded food items that they can eat. Vertebrate examples include gulls, feral pigeons, raccoon dogs, red foxes, martens and polecats sometimes scavenge for food. Hyenas also scavenge from municipal dumps in some prey-depleted districts of East Africa. The type of refuse eaten may be of plant origin (e.g. fruits, vegetables, leaves), animal origin (e.g. slaughterhouse discards), or it may be prepared food (e.g. cooked rice, bakery items). == Prehistoric scavengers ==
Prehistoric scavengers
In the prehistoric eras, the species Tyrannosaurus rex may have been an apex predator, preying upon hadrosaurs, ceratopsians, and possibly juvenile sauropods, although some experts have suggested the dinosaur was primarily a scavenger. The debate about whether Tyrannosaurus was an apex predator or scavenger was among the longest ongoing feuds in paleontology; however, most scientists now agree that Tyrannosaurus was an opportunistic carnivore, acting mostly as a predator but also scavenging when it could sense it. Recent research also shows that while an adult T. rex would energetically gain little through scavenging, smaller theropods of approximately might have gained levels similar to those of hyenas, though not enough for them to rely on scavenging. Other research suggests that carcasses of giant sauropods may have made scavenging much more profitable to carnivores than it is now. For example, a single 40 tonne Apatosaurus carcass would have been worth roughly 6 years of calories for an average allosaur. As a result of this resource oversupply, it is possible that some theropods evolved to get most of their calories by scavenging giant sauropod carcasses, and may not have needed to consistently hunt in order to survive. The same study suggested that theropods in relatively sauropod-free environments, such as tyrannosaurs, were not exposed to the same type of carrion oversupply, and were therefore forced to hunt in order to survive. == Ecological function ==
Ecological function
Scavengers play a fundamental role in the environment through the removal of decaying organisms, serving as a natural sanitation service. While microscopic and invertebrate decomposers break down dead organisms into simple organic matter which are used by nearby autotrophs, scavengers help conserve energy and nutrients obtained from carrion within the upper trophic levels, and are able to disperse the energy and nutrients farther away from the site of the carrion than decomposers. Scavenging unites animals which normally would not come into contact, and results in the formation of highly structured and complex communities which engage in nonrandom interactions. Scavenging communities function in the redistribution of energy obtained from carcasses and reducing diseases associated with decomposition. Oftentimes, scavenger communities differ in consistency due to carcass size and carcass types, as well as by seasonal effects as consequence of differing invertebrate and microbial activity. Scavengers of infected carcasses may become hosts for certain pathogens and consequently vectors of disease themselves. Likewise, the ingestion of bat carcasses infected with rabies by striped skunks (Mephitis mephitis) resulted in increased infection of these organisms with the virus. A major vector of transmission of diseases are various bird species, with outbreak being influenced by such carrier birds and their environment. An avian cholera outbreak from 2006 to 2007 off the coast Newfoundland, Canada resulted in the mortality of many marine bird species. The transmission, perpetuation and spread of the outbreak was mainly restricted to gull species who scavenge for food in the area. Similarly, an increase of transmission of avian influenza virus to chickens by domestic ducks from Indonesian farms permitted to scavenge surrounding areas was observed in 2007. The scavenging of ducks in rice paddy fields in particular resulted in increased contact with other bird species feeding on leftover rice, which may have contributed to increased infection and transmission of the avian influenza virus. The domestic ducks may not have demonstrated symptoms of infection themselves, though were observed to excrete high concentrations of the avian influenza virus. == Threats ==
Threats
Many species that scavenge face persecution globally. Vultures, in particular, have faced incredible persecution and threats by humans. Before its ban by regional governments in 2006, the veterinary drug Diclofenac has resulted in at least a 95% decline of Gyps vultures in Asia. Habitat loss and food shortage have contributed to the decline of vulture species in West Africa due to the growing human population and over-hunting of vulture food sources, as well as changes in livestock husbandry. Poisoning certain predators to increase the number of game animals is still a common hunting practice in Europe and contributes to the poisoning of vultures when they consume the carcasses of poisoned predators. == Benefits to humans ==
Benefits to humans
Highly efficient scavengers, also known as dominant or apex-scavengers, can have benefits to humans. Increases in dominant scavenger populations, such as vultures, can reduce populations of smaller opportunistic scavengers, such as rats. These smaller scavengers are often pests and disease vectors. ==In humans==
In humans
(at the end of the Battle of Berlin), on Manfred-von-Richthofen-Straße in Tempelhof borough, 1945 In the 1980s, Lewis Binford suggested that early humans primarily obtained meat via scavenging, not through hunting. In 2010, Dennis Bramble and Daniel Lieberman proposed that early carnivorous human ancestors subsequently developed long-distance running behaviors which improved the ability to scavenge and hunt: they could reach scavenging sites more quickly and also pursue a single animal until it could be safely killed at close range due to exhaustion and hyperthermia. In Tibetan Buddhism, the practice of excarnation—that is, the exposure of dead human bodies to carrion birds and/or other scavenging animals—is the distinctive characteristic of sky burial, which involves the dismemberment of human cadavers of whom the remains are fed to vultures, and traditionally the main funerary rite (alongside cremation) used to dispose of the human body. A similar funerary practice that features excarnation can be found in Zoroastrianism; in order to prevent the pollution of the sacred elements (fire, earth, and water) from contact with decomposing bodies, human cadavers are exposed on the Towers of Silence to be eaten by vultures and wild dogs. Studies in behavioral ecology and ecological epidemiology have shown that cannibalistic necrophagy, although rare, has been observed as a survival behavior in several social species, including anatomically modern humans; == Gallery ==
Gallery
File:White-backed_vultures_eating_a_dead_wildebeest.JPG|White-backed vultures feeding on a carcass of a wildebeest File:Raven scavenging on a dead shark.jpg|A jungle crow feeding on a small dead shark File:Coyoteelk.jpg|Coyote feeding on an elk carcass in winter in Lamar Valley, near Yellowstone National Park File:A polar bear (Ursus maritimus) scavenging a narwhal whale (Monodon monoceros) carcass - journal.pone.0060797.g001-A.png|A polar bear scavenging on a narwhal carcass File:An Ibiza wall lizard (Podarcis pityusensis) scavenging on fish scraps leftover from another predator - journal.pone.0060797.g001-B.png|An Ibiza wall lizard scavenging on fish scraps left over from another predator File:Red weaver ants (Oecophylla smaragdina) feeding on a dead African giant snail (Achatina fulica) - journal.pone.0060797.g001-F.png|Red weaver ants feeding on a dead giant African snail File:Feral dog eating from trash bin in Moscow 01.jpg|A feral dog scavenging for food in a trash bin in Moscow File:Squirrel eating an ice cream cone (3558009610).jpg|A gray squirrel scavenging food scraps from a trash bin in London File:A herd of 40 wild elephants at Ampara in east Sri Lanka is totally dependent on garbage from tractors DSC-9.jpg|Asian elephants scavenging for food at a municipal dump in Sri Lanka == See also ==
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