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Reining in the Wild Horses

Reining in the Wild Horses. Data & story from DASL Reference: Eagle, Asa, Garrot et al. (1993). Wildlife Society Bulletin, 21(2), 116-121. Research Question: Will sterilization of the dominant male in a wild horse herd reduce foaling (birth) rates for 2 or more years?. Background.

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Reining in the Wild Horses

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  1. Reining in the Wild Horses • Data & story from DASL • Reference: Eagle, Asa, Garrot et al. (1993). Wildlife Society Bulletin, 21(2), 116-121. • Research Question: Will sterilization of the dominant male in a wild horse herd reduce foaling (birth) rates for 2 or more years?

  2. Background • December 1985: Dominant male in wild horse bands from two Herd Management Areas vasectomized. Control group male left untreated • June 1986 – July 1988: aerial survey of bands 3-4 times a year to record number of adults and foals in the treated and untreated bands

  3. Data Analysis • Data entered into SPSS • Explore command used to produce descriptive statistics for treated and untreated groups • Clustered Bar graphs created to display findings.

  4. Program Effectiveness • Mean number of foals in the sterilized bands was 5 (range of 1 to 17) compared to a mean of 26 (range of 16 to 39) in the untreated bands • Treatment effect was observed in both herds

  5. Adjustment for Herd Size • Mean number of adults differed in the treated and untreated groups (M(trt) = 46 adults vs. M(untrt) = 174) • Calculate number of foals/number of adults to adjust for this

  6. Conclusions • Sterilization of dominant male in herd reduced average number of births by 21 foals per season (26 down to 5) • Adjusted for herd size, this represents a decrease from 1 foal per 15 adults (0.15) down to 1 foal per 10 adults (0.10) • Over time, this decrease in birth-rate will improve herd health and grazing land condition

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