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).
Location Specific Management Information
Some culling of Ovis aries has taken place in recent years (Ashmole and Ashmole, 2000 in Varnham, 2006). The Management Plan recommends a study to see if viable Prosopis seeds are found in sheep dung, and if so, that the feral flock be culled except for a few securely fenced captive animals (Pickup, 1999 in Varnham, 2006).
Campbell Is./Motu Ihupuku (sub-Antarctic) (New Zealand sub-Antarctic Islands)
The island was converted into a reserve in 1954 and a case was made to eradicate the sheep because they were thought to threaten nesting sites, the vegetation pattern, and some plant taxa. The island was divided into halves by a fence in 1970, and all sheep north of it were killed. The southern population continued to grow from 1970 to 1984. The southern half of the island was cleared of sheep in 1984 except for about 800 fenced off on a peninsula.
Results of a study (Meurk, 1982) conducted to assess the impact of the removal of sheep from the sheep-free side of Campbell island indicated that regeneration of most plant species was vigourous.
Damage to this vegetation by feral sheep, led to management for reduction of sheep populations from 1955. Sustained hunting kept the population below 5,000 and during the 1970's the population levels averaged 1500 animals. Continued threat to the habitat of the endangered palila led to the the United States District Court for the District of Hawaii ordered the State of Hawaii to remove feral goats and sheep completely and permanently from the areas of the mamane forest designated as critical palila habitat (the Mauna Kea Forest Reserve up to an elevation of 3,000 m, the Kaohe Game Management area, and the upper Waikii parcel). Eradication was completed in these areas by August 1981. However there have been influx of feral sheep from areas adjacent to the critical habitat which require periodic hunts to comply with the court order (Scowcroft and Giffin 1983).
Note: The palila is currently placed in the monotypic genus Loxioides, but in the past it was included with several other allied species in Psittirostra- (Psittirostra bailleui).
The authors (Carlile et al. 2003) of a review of four successful recovery programmes for threatened sub-tropical petrels state that recovery of nesting habitat and eradication of predators are the two most beneficial actions leading to the success of the programmes. Erosion of nesting habitat through overgrazing, and trampling by domestic stock (sheep Ovis aries and goats Capra hircus) are cited as current threats and reasons for the decline in populations of the threatened Zino's petrel (see Pterodroma madeira in IUCN Red List of Threatened Species). The endangered birds were restricted to small cliff ledges that are inaccessible to large mammals.
Zino's petrel occurs only on the heavily populated north Atlantic island of Madeira (32° 45' E, 16° 28' N) off the coast of North Africa, 900km from Portugal, to which the island belongs.
Santa Cruz Is. (US)
Ninety percent of Santa Cruz island was taken over by The Nature Conservancy which made sheep eradication its major priority. By June 1989, there were almost no sheep or cattle remaining on Conservancy lands. The National Park Service completed purchase of the eastern 10 percent of the island in 1998, removed the remaining sheep from the island's 6000-acre East End, trapping and shipping a total of about 9000 sheep to the mainland.
Klinger et al. (2001) conducted a study to monitor the response of herbaceous vegetation and endemic plant species to the eradication of the introduced herbivores. The authors state that, "Species diversity of herbaceous vegetation did not increase significantly, but total herbaceous cover increased and bare ground decreased after O. aries were eradicated from the island. New populations of two of the five rarest species on the island were discovered within seven years of the end of the eradication program, and abundance within most of the populations of these two species increased. Many of the other endemic species showed positive responses, and other studies on Santa Cruz Island indicate that communities on the island that are dominated by shrubs and trees appear to be showing rapid rates of recovery from O. aries impacts."
Socorro (Islas Revillagigedo)
In 1994, the Revillagigedo Islands were declared a biosphere reserve. There are plans to eradicate introduced mammals and conduct surveys on Clarión and Socorro.
1. Bellchambers, K., 2004. Improving the development of effective and humane trapping systems as a control method for feral goats in Australia.
2. BirdLife International 2006. Species factsheet: Puffinus auricularis. Downloaded from http://www.birdlife.org on 13/11/2006
Summary: The World Bird Database provides the information management tool through which the BirdLife Partnership manages, analyses and reports on the breadth of its scientific knowledge - Species, Important Bird Areas (IBAs) and Endemic Bird Areas (EBAs) – much of these data are available through the Data Zone. You can search for detailed information on Species, Sites and EBAs, see examples of recent analyses and download subsets of the database. Information on some 10,000 species of bird, over 8,000 IBAs and 218 EBAs is managed through the WBDB, together with BirdLife's spatial data, multimedia files, other documents and links. The database is available from: http://www.birdlife.org/datazone/index.html
This page is available from: http://www.birdlife.org/datazone/species/index.html?action=SpcHTMDetails.asp&sid=3938&m=0 [Accessed 10 September 2006]
3. Campbell, K.J & Donlan, C.J 2005, 'A review of feral goat eradication on islands', Conservation Biology, vol. 19, no. 5, pp. 1362-74.
4. Campbell, K.J, Baxter, G.S, Murray, P.J, Coblentz, B.E & Donlan, J.D in review, 'Development of a prolonged estrus effect for use in Judas goats', Applied Animal Behaviour Science.
5. Campbell, K.J, Baxter, G.S, Murray, P.J, Coblentz, B.E, Donlan, C.J & Carrion G., V in review, 'Increasing the efficacy of Judas goats by sterilisation and pregnancy termination', Wildlife Research.
6. Carlile, N., Priddel, D., Zino, F., Natividad, C and Wingate, D. B., 2003. A review of four successful recovery programmes for threatened sub-tropical petrels. Marine Ornithology 31: 185-192.
7. Daly, K & Goriup, P 1987, Eradication of feral goats from small islands, 17, International Council for Bird Preservation, Cambridge, England.
8. IUCN/SSC Invasive Species Specialist Group (ISSG)., 2010. A Compilation of Information Sources for Conservation Managers.
Summary: This compilation of information sources can be sorted on keywords for example: Baits & Lures, Non Target Species, Eradication, Monitoring, Risk Assessment, Weeds, Herbicides etc. This compilation is at present in Excel format, this will be web-enabled as a searchable database shortly. This version of the database has been developed by the IUCN SSC ISSG as part of an Overseas Territories Environmental Programme funded project XOT603 in partnership with the Cayman Islands Government - Department of Environment. The compilation is a work under progress, the ISSG will manage, maintain and enhance the database with current and newly published information, reports, journal articles etc.
9. Kirby, A. D., A. A. Smith, T. G. Benton, and P. J. Hudson. 2004. Rising burden of immature sheep ticks (Ixodes ricinus) on red grouse (Lagopus lagopus scoticus) chicks in the Scottish uplands.. Medical and Veterinary Entomology 18(1):67-70.
Summary: A study documenting the transmission of tick born diseases by sheep.
12. Meurk, Colin D., 1982. Regeneration of Subantarctic plants on Campbell island following exclusion of sheep. New Zealand Journal of Ecology 5: 51-58.
13. Mobini, S, Heath, A.M & Pugh, D.G 2002, 'Theriogenology of sheep and goats', in D.G Pugh (ed.), Sheep and goat medicine, W. B. Saunders Company, Philadelphia, pp. 129-86.
14. O'Dempsey, N 1993, Sheep self mustering - muster in your sleep, Information series QI93026. Agdex 430/75, Queensland Department of Primary Industries, Charleville, Queensland.
15. Page, Amanda; Win Kirkpatrick and Marion Massam, February 2009, Domestic Sheep (Ovis aries) risk assessment for Australia. Department of Agriculture and Food, Western Australia.
Summary: Models for assessing the risk that exotic vertebrates could establish in Australia have been developed for mammals, birds (Bomford 2003; Bomford 2006, 2008), reptiles and amphibians (Bomford 2006, 2008; Bomford et al. 2005). These Risk Assessment models have been further explored by 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. 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.
16. Parkes, J., Henzell, R. and Pickles, G. 1996. Managing Vertebrate Pests: Feral Goats. Australian Government Publishing Service: 129pp.
Summary: A comprehensive review of the history and biology of feral goats in Australia, the damage they cause, and community attitudes to feral goat management. A wide range of strategies for goat control are discussed and recommended.
17. Rudge, M. R., 1986. The decline and increase of feral sheep (Ovis aries L.) on Campbell Island. New Zealand Journal of Ecology 9: 89-100.
18. Tummons, P. 1999. Hunters, State Stir Up Legal Action Over Removal of Sheep from Mauna Kea. Environment Hawai`i, Inc. 10 (4) HOOF BEAT column.
Summary: A newspaper article documenting legal barriers and problems that occured in Hawaii eradicating populations of feral sheep.
19. U.S. Fish and Wildlife Service, undated. Determination of Endangered Status for Argyroxiphium kauense (Ka`u Silversword). U.S. Fish and Wildlife Service Division of Endangered Species: 50 CFR Part 17 RIN: 1018-AB42.
Summary: Official U.S. document placing Argyroxiphium kauense on the endagered species list. Includes the impacts sheep have had on the species.
20. Van Driesche, Jason and Roy Van Driesche, Fall 2000. Nature Out of Place: Biological Invasions in the Global Age by (Island Press, Fall 2000).
23. Youngquist (ed.), Current therapy in large animal theriogenology, 1st edn, W. B. Saunders, Philadelphia, pp. 594-8.
Results Page: 1