Importance of observer experience in finding desert tortoises

  • Freilich J
  • Larue E
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Abstract

Because surveys for the desert tortoise (Gopherus agassizii) are usually conducted by experienced observers, we conducted 2 experiments in which observers of differing experience levels searched for desert tortoises and tortoise ''sign'' (burrows, seat) in replicated 1-ha plots. Each plot was seeded with a known number of tortoise seat, realistic-looking tortoise burrows, and 9 lifelike styrofoam tortoises of 3 size classes. When observers were divided into 2 groups, experienced and inexperienced, the groups did not differ (P greater than or equal to 0.17) in their ability to find tortoises of several size classes, total tortoises, seat, or burrows. Additional analyses divided experience into novice, beginner intermediate, and advanced levels based on previous survey experience. Again, tortoise-finding was unaffected tn experience level (Ps > 0.15). Observers overestimated numbers of burrows, mistakenly counted holes made by other animals, and consistently found fewer tortoises and seat than were actually seeded in plots, Tortoise-finding skill is probably part inclination and part aptitude, We cannot say which factors may affect a person's ability to find tortoises, but previous experience, in these experiments, did not.

Author-supplied keywords

  • 1998
  • BEHAVIOR
  • Gopherus
  • agassizii
  • bias
  • desert
  • design
  • experience
  • observer
  • sampling
  • survey
  • tortoise

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Authors

  • J E Freilich

  • E L Larue

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