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RESEARCH ARTICLE
Contents Vol 37(3)

Demography of feral horses (Equus caballus): a long-term study in Tornquist Park, Argentina

Alberto L. Scorolli A B and Andrea C. Lopez Cazorla A
+ Author Affiliations
- Author Affiliations

A Departamento de Biología, Bioquímica y Farmacia, Universidad Nacional del Sur, San Juan 670, 8000 ICN, Argentina.

B Corresponding author. Email: scorolli@criba.edu.ar

Wildlife Research 37(3) 207-214 https://doi.org/10.1071/WR09059
Submitted: 15 May 2009  Accepted: 11 March 2010   Published: 18 May 2010

Abstract

Context. All over the world, invasive alien mammals present conservation problems. Feral horses are invasive in many countries and their management is challenging.

Aims. To determine the demography of feral horses in Tornquist Park, Argentina, so as to develop a quantitative basis for their management.

Methods. Ground counts of individually identified female horses were conducted monthly from 1995 to 1997 and from 2000 to 2002, and seasonally in 1998 and 1999. We calculated the age structure, foaling and survival rates of mares and analysed the effects of adult density and rainfall on demographic parameters. The population trend was calculated by fitting a logistic equation to annual adult mare counts.

Key results. The foaling rate averaged 0.55 annually and the survival rate in females averaged 0.89 for adults, 0.91 for juveniles, 0.87 for yearlings and 0.94 for foals. We found adult density, rainfall and the previous year’s rainfall to have a significant effect on fecundity but no effect on adult, juvenile and foal female survival rates. Adult density had a significant negative effect on female yearling survival; however, the effect is probably trivial. The logistic equation parameters gave r = 0.327 and carrying capacity (K) = 240 adult mares.

Conclusions. A density-dependent response is suggested. The population growth is mainly limited by low fecundity, with the reduced adult female survival probably also playing a minor role.

Implications. It is expected that the present long-term demographic study will contribute to the understanding of feral ungulate ecology and improve the management of feral populations.


Acknowledgements

We are grateful to the ranger staff at Tornquist Park, in particular Daniel Porte and Facundo Casale Pintos, for their logistical support. Thanks are due to the Ministry of Agrarian Affairs of the Province of Buenos Aires for allowing the research to be carried out and for providing facilities in the reserve. Dr Scorolli thanks Dr Michelle Walter for her constant help and encouragement during the study period. Dr Nélida Winzer and Valdemar Delhey provided key bibliography on R software and GLM/GLMM analysis. We thank Drs Lee Boyd and David Forsyth and M.Sc. Laurent Tatin for their comments on an earlier version of this work. Thanks go to Drs Lee Eberhardt, Sophie Grange and Wayne Linklater for their advice on analyses and other aspects of the manuscript. This study was financed by grants (PGI 24B/074 and 24B/110) from the Secretaría de Ciencia y Tecnología of the Universidad Nacional del Sur, Argentina.


References

Beever E. A. , and Brussard P. F. (2000). Charismatic megafauna or exotic pest? Interactions between popular perceptions of feral horses (Equus caballus) and their management and research. In ‘Proceedings of the 19th Vertebrate Pest Conference’. (Eds T. P. Salmon and A. C. Crab.) pp. 413–418. (University of California: Davis, CA.)

Berger J. (1986). ‘Wild horses of the Great Basin, Social Competition and Population Size.’ (The University of Chicago Press: Chicago, IL.)

Berman D. McK. (1991). The ecology of feral horses in central Australia. Ph.D. Thesis, University of New England, Armidale, NSW.

Boyd L. (1979) The mare foal demography of feral horses in Wyoming’s Red Desert. In ‘Symposium on the Ecology and Behavior of Wild and Feral Equids’. (Ed. R. H. Denniston.) pp. 185–204. (University of Wyoming: Laramie, WY.)

Bradshaw, C. J. A. , Field, I. C. , Bowman, D. M. J. S. , Haynes, C. , and Brook, B. W. (2007). Current and future threats from non-indigenous animals species in northern Australia: a spotlight on World Heritage Area Kakadu National Park. Wildlife Research 34, 419–436.
| Crossref | GoogleScholarGoogle Scholar | Burgos J. (1968). El clima de la Provincia de Buenos Aires en relación con la vegetación natural y el suelo. In ‘Flora de la Provincia de Buenos Aires’. (Ed. A. L. Cabrera.) pp. 33–100. Colección Científica del INTA 4 (1). (INTA: Buenos Aires.)

Burnham K. P. , and Anderson D. R. (2002). ‘Model Selection and Multimodel Inference: A Practical Information-theoretic Approach.’ 2nd edn. (Springer Verlag: New York.)

Cabrera A. (1945). ‘Caballos de América.’ (Editorial Sudamericana: Buenos Aires.)

Cabrera A. L. (1976). Regiones Fitogeográficas Argentinas. In ‘Enciclopedia Argentina de Agricultura y Ganadería’. Tomo 2, Fascículo 2. (Ediciones Acme: Buenos Aires.)

Cameron, E. Z. , Linklater, W. L. , Minot, E. O. , and Stafford, K. J. (2001). Population dynamics 1994–1998, and management of Kaimanawa wild horses. Science for Conservation (Wellington) 171, 1–165.
Crawley M. J. (2005). ‘Statistics: An Introduction Using R.’ (John Wiley and Sons: Chichester, UK.)

Crawley M. J. (2007). ‘The R Book.’ (John Wiley and Sons: New York.)

Dawson M. J. , Lane C. , and Saunders G. (2006). ‘Proceedings of the National Feral Horse Management Workshop.’ (Invasive Animals Cooperative Research Centre: Canberra.)

Dobbie W. R. , Berman D. McK. , and Braysher M. L. (1993). ‘Managing Vertebrate Pests: Feral Horses.’ (Australian Government Publishing Service: Canberra.)

Douglas C. L. , and Leslie D. M. (1996). Feral animals on rangelands. In ‘Rangeland Wildlife’. (Ed. P. R. Krausman.) pp. 281–292. (The Society for Range Management: Denver, CO.)

Duncan P. (1992). ‘Horses and Grasses. The Nutritional Ecology of Equids and Their Impact on the Camargue.’ Ecological Studies 87. (Springer Verlag: Berlin.)

Eberhardt, L. L. (1977). Optimal management policies for marine mammals. Wildlife Society Bulletin 5, 162–169.
Fowler C. W. (1987). A review of density dependence in populations of large mammals. In ‘Current Mammalogy’. (Ed. H. H. Genoways.) pp. 401–441. (Plenum Press: New York.)

Frangi, J. L. , and Bottino, O. J. (1995). Comunidades vegetales de la Sierra de la Ventana, Provincia de Buenos Aires, Argentina. Revista de la Facultad de Agronomía (La Plata) 71, 93–133.
Lever C. (1994). ‘Naturalized Animals.’ (Poyser Natural History: London.)

Linklater, W. L. , Cameron, E. Z. , Minot, E. O. , and Stafford, K. J. (2004). Feral horse demography and population growth in the Kaimanawa Ranges, New Zealand. Wildlife Research 31, 119–128.
| Crossref | GoogleScholarGoogle Scholar | Long J. L. (2003). ‘Introduced Mammals of the World. Their History, Distribution and Influence.’ (CSIRO Publishing: Melbourne.)

Loydi, A. , and Zalba, S. M. (2009). Feral horses dung piles as potential invasion windows for alien plant species in natural grassland. Plant Ecology 201, 471–480.
| Crossref | GoogleScholarGoogle Scholar | National Research Council (1980). ‘Wild and Free-roaming Horses and Burros: Current Knowledge and Recommended Research.’ (National Academy of Science: Washington, DC.)

Parkes, J. , and Murphy, E. (2003). Management of introduced mammals in New Zealand. New Zealand Journal of Zoology 30, 335–359.
Scorolli A. L. (1999). Demografía y áreas de actividad de una población de caballos cimarrones en el Parque Tornquist. Magister Thesis, Universidad Nacional del Sur, Argentina.

Scorolli A. L. (2007). Dinámica poblacional y organización social de caballos cimarrones en el Parque Provincial Ernesto Tornquist. Doctoral Thesis. Universidad Nacional del Sur, Argentina.

Scorolli, A. L. , Lopez Cazorla, A. C. , and Tejera, L. A. (2006). Unusual mass mortality of feral horses during a violent rainstorm in Parque Provincial Tornquist, Argentina. Mastozoología Neotropical 13, 255–258.
Sinclair A. R. E. (1989). Population regulation in animals. In ‘Ecological Concepts’. (Ed. J. M. Cherrett.) pp. 197–241. (Blackwell Scientific Publications: Oxford, UK.)

Siniff, D. B. , Tester, J. R. , and Mc Mahon, G. L. (1986). Foaling rate and survival of feral horses in western Nevada. Journal of Range Management 39, 296–297.
| Crossref | GoogleScholarGoogle Scholar | Walter M. J. (2002). The population ecology of wild horses in the Australian Alps. Ph.D. Thesis, University of Canberra, Australia.

Welsh D. A. (1975). Population, behavioral and grazing ecology of the horses of Sable Island, Nova Scotia. Ph.D. Thesis, Dalhousie University, Halifax, Canada.

White, P. , Ford, A. E. S. , Clout, M. N. , Engeman, R. M. , Roy, S. , and Saunders, G. (2008). Alien invasive vertebrates in ecosystems: pattern, process and the social dimension. Wildlife Research 35, 171–179.
| Crossref | GoogleScholarGoogle Scholar | Witmer G. W. , Pitt W. C. , and Fagerstone K. A. (Eds) (2007). ‘Managing Vertebrate Invasive Species: Proceedings of an International Symposium.’ (USDA–APHIS: Fort Collins, CO.)

Wolfe, M. L. (1980). Feral horse demography: a preliminary report. Journal of Range Management 33, 354–360.
| Crossref | GoogleScholarGoogle Scholar | Zuur A. F. , Ieno E. N. , Walter N. J. , Saveliev A. A. , and Smith G. M. (2009). ‘Mixed Effects Models and Extensions in Ecology with R.’ (Springer: New York.)