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Influences of immunocontraception on time budgets, social behavior, and body condition in feral horses

By J. I. Ransom, B. S. Cade, N. T. Hobbs

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Managers concerned with shrinking habitats and limited resources for wildlife seek effective tools for limiting population growth in some species. Fertility control is one such tool, yet little is known about its impacts on the behavioral ecology of wild, free-roaming animals. We investigated influences of the immunocontraceptive porcine zona pellucida (PZP) on individual and social behavior in bands of feral horses (Equus caballus) in three discrete populations and used 14 hierarchical mixed effect models to gain insight into the influences of PZP treatment on feral horse behavior. A model of body condition was the strongest predictor of feeding, resting, maintenance, and social behaviors, with treated females allocating their time similarly to control females. Time spent feeding declined 11.4% from low condition to high condition females (F1,154=26.427, P<0.001) and was partially reciprocated by a 6.0% increase in resting (F1,154=7.629, P=0.006), 0.9% increase in maintenance (F1,154=7.028, P=0.009), and 1.8% increase in social behavior (F1,154=15.064, P<0.001). There was no difference detected in body condition of treated versus control females (F1,154=0.033, P=0.856), but females with a dependent foal had lower body condition than those without a foal (F1,154=4.512, P=0.038). Herding behavior was best explained by a model of treatment and the interaction of band fidelity and foal presence (AICc weight=0.660) which estimated no difference in rate of herding behavior directed toward control versus treated females (F1,102=0.196, P=0.659), but resident females without a dependent foal were herded 50.9% more than resident females with a foal (F3,102=8.269, P<0.001). Treated females received 54.5% more reproductive behaviors from stallions than control mares (F1,105=5.155, P=0.025), with the model containing only treatment being the most-supported (AICc weight=0.530). Treated and control females received harem-tending behaviors from stallions equally (F1,105=0.001, P=0.969) and agonistic behaviors from stallions equally (F1,105 <0.001, P=0.986). Direct effects of PZP treatment on the behavior of feral horses appear to be limited primarily to reproductive behaviors and most other differences detected were attributed to the effects of body condition, band fidelity, or foal presence. PZP is a promising alternative to traditional hormone-based contraceptives and appears to contribute few short-term behavioral modifications in feral horses.

Date 2010
Publication Title Applied Animal Behaviour Science
Volume 124
Issue 1/2
Pages 51-60
ISBN/ISSN 0168-1591
DOI 10.1016/j.applanim.2010.01.015
Author Address U.S. Geological Survey, 2150 Centre Ave., Bldg. C, Fort Collins Science Center, Fort Collins, CO 80526, USA.ransomj@usgs.gov
Additional Language English
Cite this work

Researchers should cite this work as follows:

  1. Animal behavior
  2. Animal ecology
  3. Animal nutrition
  4. Behavior and behavior mechanisms
  5. Biological resources
  6. Birth
  7. Body condition
  8. Contraception
  9. Ecology
  10. Effect
  11. Feeding
  12. Feral animals
  13. Fertility.
  14. Habitats
  15. Horses
  16. Mammals
  17. Meat animals
  18. models
  19. peer-reviewed
  20. Pigs
  21. population growth
  22. predictions
  23. predictors
  24. Reproduction
  25. Social behavior
  26. Swine
  27. Wild animals
  28. wildlife
  29. Zoology
  1. peer-reviewed