Journal of Ethology

, Volume 24, Issue 2, pp 147–154 | Cite as

Predictors of biting fly harassment and its impact on habitat use by feral horses (Equus caballus) on a barrier island

  • David M. PowellEmail author
  • David E. Danze
  • Michael A. Gwinn


Feral horses on Assateague Island, Maryland, were observed in June and August 2000 to determine what behavioral and ecological factors affect the intensity of biting fly harassment and whether habitat use by horses was influenced by biting flies. Fly counts and frequencies of comfort movements (i.e., movements designed to dislodge insects) were recorded during focal animal samples, as well as data on sex, group size, habitat type, temperature, humidity, wind speed, and behavior. Seasonal habitat use patterns were assessed using 7 years of monthly census data on the horses. The number of biting flies on the horse was affected by horse sex, habitat, temperature, and group size. The number of comfort movements a horse showed was affected by habitat, temperature, wind speed, group size, and number of horses within one body length of the focal. The number of comfort movements made by a horse was found to be highly correlated with fly numbers. Though marshes were used most throughout the year, the pattern of use of dune, scrub, and human-altered habitats reflects a pattern of biting fly avoidance and refuge-seeking by the horses.


Horses Fly Barrier Island Habitat use Harassment 



We would like to thank Carl Zimmerman, Jack Kumer, and Alison Turner of the National Parks Service for their assistance with this research. Edward Barrows (Georgetown University) also provided helpful comments and assistance. The manuscript was improved by comments from two anonymous reviewers. This research was approved by the Georgetown University Animal Care and Use Committee.


  1. Altmann P, Dittmer D (1968) Metabolism. Federation of American Societies for Experimental Biology, Bethesda, MDGoogle Scholar
  2. Duncan P, Cowtan P (1980) An unusual choice of habitat helps Camargue horses to avoid blood-sucking flies. Biol Behav 5:55–60Google Scholar
  3. Duncan P, Vigne N (1979) The effects of group size in horses on the rates of attack by blood-sucking flies. Anim Behav 27:623–625CrossRefGoogle Scholar
  4. Espmark Y, Langvatn R (1979) Lying down as a means of reducing fly harassment in red deer (Cervus elaphus). Behav Ecol Sociobiol 5:51–55CrossRefGoogle Scholar
  5. Hamilton WD (1971) Geometry for the selfish herd. J Theor Biol 31:295–311CrossRefPubMedGoogle Scholar
  6. Hargrove JW, Holloway MTP, Vale GA, Gough AJE, Hall DR (1995) Catches of tsetse (Glossina spp.) (Diptera: Glossinidae) from traps and targets baited with large doses of natural and synthetic host odour. Bull Entomol Res 85:215–227Google Scholar
  7. Hart BL (1990) Behavioral adaptations to pathogens and parasites: five strategies. Neurosci Biobehav Rev 14:273–294CrossRefPubMedGoogle Scholar
  8. Hart BL (1994) Behavioural defense against parasites: interaction with parasite invasiveness. Parasitology 109:139–151PubMedGoogle Scholar
  9. Hughes RD, Duncan P, Dawson J (1981) Interactions between Camargue horses and horse flies (Tabanidae). Bull Entomol Res 71:227–242Google Scholar
  10. Keiper R, Berger J (1982) Refuge-seeking and pest avoidance by feral horses in desert and island environments. Appl Anim Ethol 9:111–120CrossRefGoogle Scholar
  11. Knox P, Hays K (1972) Attraction of Tabanus spp. (Diptera: Tabanidae) to traps baited with carbon dioxide and other chemicals. Environ Entomol 1:323–326Google Scholar
  12. Mooring M, Hart B (1992) Animal grouping for protection from parasites: selfish herd and encounter-dilution effects. Behaviour 123:173–193Google Scholar
  13. Mooring MS, Fitzpatrick TA, Fraser IC, Benjamin JE, Reisig DD, Nishihira TT (2003) Insect-defense behavior by desert bighorn sheep. Southwest Nat 48:635–643CrossRefGoogle Scholar
  14. Morgan N, Lee R (1977) Vegetative barriers influence flight direction of saltmarsh greenheads. Mosq News 37:263–268Google Scholar
  15. Rockel E, Hansens E (1970a) Emergence and flight activity of salt-marsh horseflies and deerflies. Ann Entomol Soc Am 63:27–31Google Scholar
  16. Rockel E, Hansens E (1970b) Distribution of larval horseflies and deerflies of a New Jersey saltmarsh. Ann Entomol Soc Am 63:681–684Google Scholar
  17. Rubenstein DI, Hohmann ME (1989) Parasites and social behavior of island feral horses. Oikos 55:312–320Google Scholar
  18. Rutberg A (1987) Horse fly harassment and the social behavior of feral ponies. Ethology 75:145–154Google Scholar
  19. Smythe R, Goody P (1972) The horse. JA Allen, LondonGoogle Scholar
  20. Tashiro H, Schwardt H (1949) Biology of the major species of horse flies of central New York. J Econ Entomol 42:269–272Google Scholar
  21. Tashiro H, Schwardt H (1953) Biological studies of horseflies in New York. J Econ Entomol 46:813–822Google Scholar
  22. Tyler SJ (1972) The behaviour and social organization of the New Forest ponies. Anim Behav Monogr 5:85–196Google Scholar

Copyright information

© Japan Ethological Society and Springer-Verlag 2005

Authors and Affiliations

  • David M. Powell
    • 1
    Email author
  • David E. Danze
    • 2
  • Michael A. Gwinn
    • 3
  1. 1.Department of MammalogyWildlife Conservation Society, Bronx ZooBronxUSA
  2. 2.Administrative Management Systems Support Branch, Office of the Chief Technology OfficerSmithsonian InstitutionWashington DCUSA
  3. 3.Department of BiologyGeorgetown UniversityWashington DCUSA

Personalised recommendations