As scavengers or necrophages (from Greek νεκρός, nekros "dead" and φα [γ] ί, fa [g] í "food") are referred to animals whose diet mainly or partly from cadavers have consists of animals that they killed themselves . Due to the way they feed on dead organic matter, they can be counted among the saprophages . Scavenging, however, is a specialized type of food acquisition with little relationship to other types of saprophagy. The scavengers are ecologically grouped into a guild .
Carrion as a source of food
Contrary to popular belief, the life of most vertebrates does not end with predators . In the African savannas z. For example, it is estimated that around two thirds of ungulates are not victims of predators, but rather die as a result of lack of food, parasites, disease or accidents. Even small animals such as mice with their numerous predators die around 40% of them naturally . Although the supply of carrion can vary widely between different habitats and at different times, it is far higher than is often assumed. In conventional studies of vertebrate nutrition, this is often overlooked because e.g. B. from intestinal content analyzes it can hardly be deduced whether the food was freshly taken in dead or as carrion, or because the food is only specified according to the animal species used. In numerous studies, laid out animal carcasses were predominantly and quickly used by scavenging animal species. This also applies to most of the undercover corpses, e.g. B. within forests or under a blanket of snow.
However, the use of carrion as a food source presents a number of difficulties. Animal corpses are broken down by bacteria from the moment they die. Numerous typical Aasbesiedler as Clostridium perfringens or Salmonella produce toxins ( toxins ). This has been interpreted as an ecological competitive reaction to defend the food base against animal scavengers. Vertebrates also compete with invertebrate scavengers, particularly insect species. Significant species that specialize in carrion are in particular beetles such as the carrion beetles (e.g. gravedigger ) and the larvae (maggots) of numerous species of flies, especially those from the meat fly and blowfly family . In tropical Africa it was observed that smaller animal corpses of 2 to 10 kg body mass were almost completely consumed by fly maggots within three days. The bacteria depend on the work of the insects: corpses that are not infested by insects often mummify to a large extent and are microbially degraded much more slowly.
In most habitats, the existing biomass of the living animals is always greater than that of the (relatively fresh) dead. It follows that relatively few vertebrate species specialize in carrion as an obligatory source of food. In the case of mammals or reptiles, carrion specialists are even completely unknown. Also known as scavengers such as the hyenas , as far as is known, eat more living than dead food and are therefore, at least to a considerable extent, predators. A group of bird species, the vultures, specializes at least predominantly in carrion . This is mainly explained by the great advantages of flight. A flying bird can search huge areas in a short time, whereby (in the case of gliding) the energetic costs are very low for it. In addition to the always very good eyesight, some, such as the New World vultures of the genus Cathartes , have also acquired an excellent sense of smell. "Vulture" is an ecological, not a systematic category: The birds named in this way are partly not related to each other, but have acquired the characteristic features such as the long, bare and flexible neck and the wide wings (for optimal gliding) convergent . Most of the other scavengers are predatory species that ingest carrion to a greater or lesser extent alongside live prey. There is no predator who would spurn a freshly dead specimen of a popular type of prey, which would not be a scavenger at least occasionally. Of course, this does not mean that predatory species use carrion indiscriminately or in equal proportions. Rather, there are a number of species that use carrion regularly and in fairly high proportions as part of the food spectrum. In dense forests and in arctic latitudes, where bird species are disadvantaged due to spatial resistance and poor thermals, mammal species can be more important than birds. Is known z. B. in Central Europe a high importance of carrion as a food source z. B. for red fox , buzzard and corvids , but also for sea eagles . Local buzzards have specialized strongly in victims of car traffic, so that you can often see them sitting along highways. Carrion can be essential for many of these species as part of the food source during times of starvation, especially in snowy winters. In regions where vultures are found, however, these are always the dominant scavengers. In a study in Panama , vultures found almost two thirds of animal corpses, mammals only about 5 percent.
Importance in forensics
Scavengers have become particularly important in connection with criminology in recent years . A separate area of forensics has developed there, known as entomological forensics . In this area, insects colonizing corpses are used to investigate deaths and decomposition .
- T. Mebs, D. Schmidt: The birds of prey in Europe, North Africa and the Middle East. Franckh-Kosmos, Stuttgart 2006, ISBN 3-440-09585-1 .
- Travis L. DeVault, Olin E. Rhodes Jr., John A. Shivik: Scavenging by vertebrates: behavioral, ecological, and evolutionary perspectives on an important energy transfer pathway in terrestrial ecosystems. In: Oikos. 102, 2003, pp. 225-234. (download)
- ^ DC Houston: The adaptations of scavengers. In: ARE Sinclair, MN Griffiths (Ed.): Serengeti, dynamics of an ecosystem. Univ. of Chicago Press, 1979, pp. 263-286.
- ^ RJ Putman: Energetics of the decomposition of animal carrion. Ph. D. thesis. University of Oxford, 1976.
- ↑ John A. Shivik: Are Vultures Birds, Snakes and Do Have Venom, Because of macro- and Microscavenger Conflict? In: BioScience. 56 (10), 2006, pp. 819-823. doi : 10.1641 / 0006-3568 (2006) 56 [819: AVBADS] 2.0.CO; 2
- ↑ SM Cooper, KE Holekamp, L. Smale: Aseasonal feast: long-term analysis of feeding behavior in the spotted hyaena (Crocuta crocuta). In: African Journal of Ecology. 37, 1999, pp. 149-160. doi: 10.1046 / j.1365-2028.1999.00161.x
- ↑ Nuria Selva, Miguel A Fortuna: The nested structure of a scavenger community. In: Proceedings of the Royal Society. Series B 274, 2007, pp. 1101-1108. doi: 10.1098 / rspb.2006.0232
- ^ LG Gomez, DC Houston, P. Cotton, A. Tye: The role of greater yellow-headed vultures Cathartes melambrotus as scavengers in neotropical forest. In: Ibis. 136, 1993, pp. 193-196. doi: 10.1111 / j.1474-919X.1994.tb01084.x