Taxonomic name: Ovis aries Linnaeus, 1758
Synonyms: Ovis aries musimon Pallas, 1762 , Ovis aries ophion Blyth, 1841 , Ovis musimon musimon Pallas, 1762 , Ovis musimon ophion Blyth, 1841 , Ovis musimon Pallas, 1762 , Ovis ophion Blyth, 1841 , Ovis orientalis Gmelin, 1774
Common names: mouflon, sheep
Organism type: mammal
Ovis aries (sheep) are an ungulate mammal believed to have originated in Europe. While humans have domesticated the majority of sheep, feral populations exist. These populations are causing impacts on the native diversity of plant species, especially on islands. The impact their grazing has on vegetation is known to cause declines in rare and endangered bird species and other native ungulate species.
There exist over 200 distinct breeds of sheep Ovis aries. The breeds differ in their physical characteristics. Female sheep tend to be smaller than males by a quarter to one third of male size- head and body lenght 1,200-1,800mm and shoulder height 650-1,270mm. O. aries have a vertical cleft and narrow snout completely covered with short hair except on the margins of the nostrils and lips. Wild O. aries have tails between 70-150mm but in domestic O. aries tails may be larger and used as a fat reserve, although these long tails are removed on most commercial farms. The skulls of domesticated O. aries differ from those of wild sheep in that the eye socket and brain case are reduced. The genus Ovis is characterized by the presence of glands situated in a shallow depression in the lacrimal bone, the groin area, and between the two main toes of the foot. These glands secrete a clear semi-fluid substance that gives domestic O. aries their characteristic smell. Selection for economically important traits has produced domestic O. aries with or without wool, horns and external ears. Colouration ranges from milky white to dark brown and black (Reavill, 2000).
agricultural areas, desert, natural forests, planted forests, range/grasslands, ruderal/disturbed, scrub/shrublands
Sheep (Ovis aries) are extremely versatile and exist in a wide variety of habitats worldwide ranging from temperate mountain forests to desert conditions (Grzimek 1990, MacDonald 1984 in Reavill, 2000).
Establishment of feral herbivores like sheep (Ovis aries) have had significant ecological impacts on island ecosystems. Island ecosystems are particularly vulnerable to herbivores as insular plants in these ecosystems evolved largely in the absence of large herbivores, therefore lacking in defences against them. Increased bare ground followed by increased erosion are some of the other impacts (Van Vuren and Coblentz, 1987). Van Vuren and Coblentz (1987) in their study on the ecological effects of feral sheep on Santa Cruz Island, California observe that feral sheep are forage generalists when compared to domestic sheep on mainland. Feral sheep diet include annual grasses, forbs and also a substantial quantity of shrubs. The authors summarise the ecological impacts of feral sheep: consumption of endemic species by feral sheep could potentially cause decline in their population levels; loss of vegetation due to trampling while grazing; compaction of the soil and therefore changes in the soil structure; soil erosion due to removal of vegetration and denudation of the soil; removal of hebaceous vegetation caused changes in the grassland community, reduction of litter and a decline in the recruitment of seedlings. Alteration in the plant community led to decrease in species diversity.
Grazing and browzing of herbaceous vegetation, and stripping of bark by feral sheep and other introduced mammals (cattle (Bos taurus), Mouflon sheep (Ovis musimon), and feral goats (Capra hircus)) have led to exposure of soil to erosion and degradation of forests on Mauna Kea (Scowcraft and Sakai 1983). Welsh (2002) adds that, "O. aries are extensive and destructive herbivores. They have been found to decrease populations of the mamane (Sophora chrysophylla), an endemic leguminous tree, by stripping the bark off thus facilitating damage from insects and and other disease causing organisms". Results of a study (Scowcroft and Giffen 1983) which evaluated the regeneration of vegetation and forests inside and outside sheep exclosures located in heavily browsed portions of the mamane forest of Mauna Kea, indicated feral sheep browsing suppresses regeneration of mamane and three other endemic species, Hawai‘ian bent, heu-pueo, and aheahea.
Liu and Jiang (2004) report that, "The most important food competitor of the critically endangered Przewalski's gazelle (see Procapra przewalskii in IUCN Red List of Threatened Species) is the domestic Tibetan sheep (O. aries) in the steppe and deserts around Qinghai Lake on the Qinghai-Tibet Plateau."
Kirby et al. (2004) state that, "The sheep tick Ixodes ricinus (L.) is an ectoparasite of major economic and pathogenic importance in Scotland. Its distribution in the Scottish uplands is assumed to be governed by the abundance and distribution of its definitive hosts (deer and O. aries) and climatic variables such as temperature and rainfall.
Reavill (2000) observes that, "Sheep (Ovis aries) is one of the most economically significant species on the planet. Since their domestication between 9000 and 11000 years ago they have been a source of meat, milk, wool and hides in nearly every country. In some cultures O. aries are considered highly useful as a sacrificial animal. The versatility of the species contributes to its economic significance as large herds of animals can be maintained in many environments at relatively low costs. Besides their usefulness in an agricultural sense, O. aries have become important as a tool for scientific research. Because of their large size and low maintenance costs they make an ideal model for a great deal of scientific research."
Native range: It is believed that sheep (Ovis aries) originated in Europe (Welsh, 2002).
Known introduced range: Sheep have been introduced and domesticated around the world.
Introduction pathways to new locations
Acclimatisation societies: The Rare Breeds Conservation Society of New Zealand (2003) states that, "New Zealand has no native wild land mammals but with the advent of European settlement a steady stream of animals was introduced, starting with Cook's visits in the 1770s and continuing until this day. Many were deliberately released into the wild, but a number of species of domestic livestock also escaped into the more inaccessible country, particularly in the earlier days of farming when good fencing was not widespread."
Preventative measures: Risk Assessment models for assessing the risk that exotic vertebrates could establish in Australia have been further explored by the Western Australia Department of Agriculture & Food (DAFWA) to confirm that they reasonably predict public safety, establishment and pest risks across a full range of exotic species and risk levels.
The Risk assessment for the Domestic Sheep (Ovis aries), has been assigned a VPC Threat Category of EXTREME.
Mammals and birds were assessed for the pest risk they pose if introduced to Australia, by calculating Vertebrate Pests Committee (VPC) Threat Categories. These categories incorporate risk of establishing populations in the wild, risk of causing public harm, and risk of becoming a pest (eg causing agricultural damage, competing with native fauna, etc). The 7-factor Australian Bird and Mammal Model was used for these assessments.
Physical: Management strategies for sheep (O. aries) include hunting and the use of fencing to keep animals out (Welsh, 2002). Due to the behavioural similarities between sheep and goats (see Capra hircus), management strategies and hunting techniques for goats work equally well for sheep, although some minor variations may be required for each technique (this is also the case with goats, depending on vegetation, terrain, naivety). Please see Campbell & Donlan, 2005; Parkes et al. 1996 and Daly & Goriup, 1987 for more details on management strategies and hunting techniques for goats. Trapping of sheep at waterpoints or other limited resources (e.g. salt licks in some areas) can be highly effective. Please see O'Dempsey, 1993 for methods.
The use of Judas sheep as a hunting method could be applied quite easily; sheep are highly social animals and will search for conspecifics when isolated. Techniques like sterilisation, termination of pregnancy and inducing a prolonged estrus in goats for increasing their efficacy as Judas goats could be adapted for sheep. Epididymectomy can be conducted efficiently in rams with the procedures indicted for male goats. Tubal occlusion could similarly be applied in ewes as described for does. Pregnancy termination in the ewe isn't as straight-forward as it is in goats. In the first 55 days of pregnancy, abortion can be induced with prostaglandins (6 mg PGF2alpha / 58kg body weight), after 55 days pregnancy termination with prostglandins is unlikely (Stellflug et al. 1997). Incorporating cesarean section with sterilisation procedures may be the most effective means of ensuring pregnancy is terminated prior to deployment of Judas sheep. The procedure for cesarean section on sheep is outlined by Mobini et al. 2002.
(Karl Campbell., pers.comm., September 2005).
Sheep (Ovis aries) are extremely hardy animals and can survive on a diet consisting of only cellulose, starch or sugars as an energy source and a nitrogen source which need not be protein. In general, O. aries feed mainly on grasses while in pastures and can be fed a wide variety of hays and oats. Considerable research has been done on sheep nutritional requirements, and feed substitution tables are present in Ensminger's 1965 "The Stockman's Handbook". Grazing O. aries ingest a large amount of food in a short time, then retire to rest and rechew the ingested matter. O. aries spend their day alternating between these periods of grazing and ruminating. O. aries has a large and complex stomach which is able to digest highly fibrous foods that can not be digested by many other animals. Its modest nutritional requirements contribute to its economic significance.(Hecker 1983, Ensminger 1965 in Reavill 2000).
Sheep (Ovis aries) breeds on a seasonal basis, determined by day length, with females (ewes) first becoming fertile in the early fall and remaining fertile through midwinter. Estrus cycles range between 14 and 20 days with 17 as the average. Females are in heat on average for 30 hours. Males (rams) are fertile year round and most domestic sheep breeders use 1 ram to 25 to 35 ewes. Gestation averages 148 days with most lambs born in mid spring. One or two lambs, which are able to stand and suckle within a few minutes of birth, are born to each ewe. Both male and female lambs reach sexual maturity within one year. (Ensminger 1965 in Reavill 2000).
Réale et al. (2000) states that, "Although humans have modified the rutting and lambing seasons of O. aries, some feral populations show highly synchronized estrus and lambing periods that relate to latitude (Jewell 1989 ). These herds were assumed to have recovered that synchrony because of the high adaptive value of spring lambing."
Reviewed by: Dr Dirk Van Vuren Professor and Department Chair Wildlife, Fish, & Conservation Biology University of California Davis USA
Principal sources: Van Vuren, D. and B.E. Coblentz. 1987. Some ecological effects of feral sheep on Santa Cruz Island.
Compiled by: IUCN SSC Invasive Species Specialist Group
Updates with support from the Overseas Territories Environmental Programme (OTEP) project XOT603, a joint project with the Cayman Islands Government - Department of Environment
Last Modified: Wednesday, 26 May 2010