Shawave Follow-Up

The roundup yielded 594 studs and 757 mares.  The sex of the foals was not given.

Do these numbers look like they came from a herd that’s 50% males and 50% females?

The total number of adults is 1,351, with 44% studs and 56% mares.  The expected range of variation can be found from basic statistical formulas, where n = 1,351 and p = .50.

Lower limit = .50 – 3 × Sqrt[.50 × (1 – .50) ÷ 1,351] = .459 = 45.9%

Upper limit = .50 + 3 × Sqrt[.50 × (1 – .50) ÷ 1,351] = .541 = 54.1%

The percentage of studs (or mares) in the total should fall between 45.9% and 54.1%, assuming they were gathered at random from a herd that’s 50% males and 50% females.

The observed percentages fall outside these limits, so one or more assignable causes should be sought.

Perhaps the pre-gather composition of the herd was not 50% males and 50% females.

Another possibility is that the contractor targeted family bands.  Leaving bachelor bands on the range would skew the sex ratio of the herd in favor of males, slowing population growth and reducing the impact on other mandated uses of public lands.

Can you think of other explanations?