The Management of Brandt’s Vole in Mongolia: Toward an Ecologically Based Means of Control
Peter Zahler1, L. Dolgormaa2, Lyn A. Hinds3 and Andrew T. Smith4
1 Wildlife Conservation Society, P.O. Box 485, Ulaanbaatar 211238, Mongolia e-mail: email@example.com
2 WWF-Mongolia, Hydrometeorological and Environmental Monitoring Agency, Building Room 303, Ulaanbaatar-46, Mongolia e-mail: firstname.lastname@example.org
3 CSIRO Sustainable Ecosystems, GPO Box 284, Canberra, ACT 2601, Australia e-mail: Lyn.Hinds@csiro.au
4 School of Life Sciences, Box 874501, Arizona State University, Tempe, AZ 85287-4501, USA e-mail: email@example.com
The Brandt’s vole (Lasiopodomys [=Microtus] brandti) inhabits much of the Mongolian steppe and adjacent grasslands in China and Russia. This small rodent has a high reproductive capacity, and local populations may increase in numbers and reach periodic peaks, or outbreaks, that occur in cycles of between 3-14 years. Brandt’s voles live in family groups, store plant material for over-winter consumption, and show an annual cycle of abundance. The density and height of vegetation influence their habitat selection, with their preference being for areas where the grass is short, between 30-130 mm (Zhong et al. 1999). There is an over-winter decline in numbers of voles that is density-dependent, i.e., populations at a high autumn density decrease at a faster rate over winter than populations at low autumn density. During the breeding season, the rate of increase in the population is not density dependent; the rate of increase is a non-linear response to the height and cover of grass. Population growth rates are lowest in conditions of very short, sparse grass that provides insufficient food, and in tall, dense grass that probably disrupts social interactions and interferes with detection of predators (Zhang et al., 2003). Brandt’s voles are an eruptive species with outbreaks occurring episodically – for example there have been 17 severe outbreaks in Inner Mongolia in the last 50 years (Zhang et al. 2003). They have been considered a pest species because they compete with livestock, contribute to soil disturbance through their burrowing activities (and can therefore potentially influence grassland desertification), and are reservoirs for diseases such as bubonic plague. At high population densities, voles can negatively affect grasslands through their grazing. However, recent scientific studies have shown that Brandt’s voles are short-grass specialists, and that vole outbreaks are more likely if areas are overgrazed. The frequency of outbreaks has increased in the last 20 years compared to the previous 20 years, and this has coincided with an approximate 5-fold increase in livestock numbers (Zhang et al. 2003). At the same time, Brandt’s voles are a critical part of the steppe ecosystem, and may qualify as a “keystone species” – e.g., their occurrence may have a greater effect on ecosystem processes and general biodiversity than their numbers alone might suggest (Kotliar et al., 1999; Smith and Foggin, 1999; Lai and Smith, 2003). Brandt’s voles cycle and aerate soil through their burrowing efforts, and they affect vegetation around their colonies that can (during non-outbreak years) encourage a landscape mosaic of successional plant diversity (Samjaa et al., 2000). Brandt’s voles are also an important prey species for a wide range of carnivores, from foxes, polecats and Pallas’ cats to saker falcons, upland buzzards, and steppe eagles (Samjaa et al., 2000).
Management Issues: Bromadiolone In recent years the Mongolian Government has been spending between about US$300,000- $800,000 each year on poisoning campaigns against Brandt’s voles. The main rodenticide used in this campaign over the last few years is Bromadiolone. Unfortunately, this poisoning campaign has had little long-term effect on the target species, but it has had a serious negative effect on mammalian predators, raptors, cranes, various passerines, livestock, and even human health (Tseveenmyadag & Batbayar 2002). According to a report from the Ministry for Food and Agriculture in 2002, at least one person has died from this poison, and others have been hospitalized because of it. Additionally many livestock have died as well as significant numbers of birds and wildlife, including those that are the natural predators on voles. Also, current control efforts are often implemented during the height of outbreaks. This is inefficient as usually in the following winter, vole populations decrease naturally and without the need for control efforts. At the same time, poor safety methods involving processing and distribution of the poison have threatened the health of workers and community members involved in the poisoning campaign. There are three main classes of rodenticide in use today; acute poisons, first generation anticoagulants (e.g., warfarin) and second generation anticoagulants. Zinc phosphide, an acute poison, was used in Mongolia until 2000, when it was replaced by Bromadiolone. Bromadiolone is one of the ‘second-generation’ anti-coagulant rodenticides. The following are some facts related to Bromadiolone (WHO 1995):
- Bromadiolone is a vitamin K antagonist. The main site of its action is the liver. It functions as an anticoagulant and causes haemorrhaging. Bromadiolone may be absorbed from the gastrointestinal tract, from the skin, or from the lung. This means that it will act as a poison through ingestion, from contact with the hand or other body part, or through breathing in the material. Bromadiolone may accumulate in the liver and reach toxic levels over time with repeated exposure.
- In the case of humans, the main features of Bromadiolone poisoning are excessive bruising, nose and gum bleeding, and blood in urine and faeces in the less severe cases. Bleeding from several organs within the body can lead to shock and possibly death in the more severe cases. The onset of the signs of poisoning may not be evident until a few days after ingestion.
- Poor placement of Bromadiolone may allow poisoning of non-target species, primary poisoning through consumption of bait and secondary poisoning through consumption of poisoned rodents. This may negatively affect the natural predators of Brandt’s voles, as well as endangered wildlife, livestock, and children and other people who may not be aware of the danger.
- At the present time, Mongolia is still using fixedwing aircraft for aerial application. However, because of the highly toxic nature of Bromadiolone and its ability to poison a wide class of animals including humans, the World Health Organization (WHO 1995) strongly recommends against aerial application.
1. Stop Bromadiolone use in pastures by 2005 Stop using Bromadiolone for eradication of Brandt’s vole in open pastureland by the end of 2005.
2. Use Bromadiolone based only on WHO Guidelines After 2005, use Bromadiolone only in enclosed spaces and only based on requirements of the World Health Organization (WHO 1995).
3. Re-allocate government funds for the development and implementation of nonchemical control methods Spend the government budget presently used for purchase and application of Bromadiolone for a non-chemical control program to control Brandt’s voles. These government funds should be spent in the following manner: a) Pilot field projects: Organize contracted work and provide financial support to
i. Field-test various non-chemical methods of control of Brandt’s voles,
ii. Field-test combined herd management and pest control to create grassland conditions that minimize outbreaks of Brandt’s voles, and
iii. Apply the most successful combination of herd management and non-chemical methods for Brandt’s vole control over broader areas.
b) Identify appropriate sites for control Use non-chemical methods for Brandt’s vole management only at locations identified by local government inspectors as potential problem areas, such as populated locations or water sources.
c) Identify appropriate timing of control Use non-chemical methods of Brandt’s vole management only during relevant in proper seasons, before the increase in population growth, rather than at peak periods, as shortly after peak periods (during winter) voles die off by themselves with no need of management action.
4. Raise awareness of the problems with use of Bromadiolone Advertise widely to the public the dangers related to and reasons for not using Bromadiolone and other toxic chemicals in the pasture.
5. Train local people Using researchers and professionals, organize training for local people in efficient and effective use of non-chemical management methods for Brandt’s voles.
6. Encourage natural controls Actively encourage natural controls including wildlife and birds that feed on Brandt’s voles to maintain the natural balance of the steppe, including:
a) Stop hunting of carnivore species including foxes, falcons, etc. and use methods that minimize the impact of rodent control on non-target species.
b) Plant trees and bushes or construct artificial nests for raptor species that feed on Brandt’s voles; monitor these sites and perform experimental studies to determine if they are successful in controlling Brandt’s voles.
7. Develop a grassland management plan Create an organized grassland use and management plan by identifying livestock carrying capacity but maintaining flexibility in herd management to maintain grassland biomass and species composition, taking into account betweenyear variability in climate (and perhaps climate shifts); alternating, saving and restoring grassland areas; and by identifying potential areas to grow animal feed.
8. Work with local herders Train and work with local herders to assist them in implementing sustainable grassland management plans; consider creating herder cooperatives to collectively manage grasslands.
9. Create soum grassland managers Create full time-grassland managers at soum levels to ensure reasonable numbers of productive livestock and avoid overgrazing.
10. Create yearly soum Grassland Survey and Management Plan Ensure that each soum performs a yearly survey and assessment of grassland in their region and plans grazing schemes according to an agreed schedule.
11. Restore degraded grasslands Restore degraded land into grassland, re-grow unused roads for grassland use, and restore and re-grow the post mining sites. The workshop also developed a suite of recommendations for Mongolian research agencies and non-government and international organizations:
12. Initiate field research program Support government actions against Brandt’s voles through the study of international methods of prevention of Brandt’s vole’s population outbreaks and implement those methods as pilot field projects at specific locations.
13. Create long-term monitoring program Organize a long-term monitoring program to identify locations with increased Brandt’s vole populations and develop a method to predict years of vole outbreaks.
14. Study alternative vole uses Study ways and technologies to use Brandt’s vole biomass productively.
15. Organize management and training Increase grassland management activities and organize educational training workshops on how to manage Brandt’s vole populations.
16. Increase awareness Publish booklets and information brochures to educate the public on prevention of Brandt’s vole population outbreaks.
17. Promote results Promote, organize and implement practical results of pilot projects and research studies.
The International Brandt’s Vole Workshop was funded by the Wildlife Conservation Society, WWFMongolia, the United States Agency for International Development, the UNDP-GEF Sustainable Grassland Management Project, and the UNDP-GEF Eastern Steppe Biodiversity Project. Special thanks must go to the Mongolian Ministry of Agriculture and the Mongolian Ministry of Nature and Environment for their participation and encouragement. We would also like to express our gratitude to A. Laurie, J. Chimeg, D. Negue, T. Damdin, B. Battur, D. Galbadrakh, Borgil, N. Batsaikhan, B. Lhagvasuren, R. Risebrough and the many other workshop participants for providing their expertise and enthusiasm in developing these recommendations.
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