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

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

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.

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

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

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