The Park Service said in a news release today that 117 horses were living on the barrier island at the end of 2020, up from 111 at the end of 2019. The growth rate was 5.4%.
The average lifespan was eleven years and no mares were treated with contraceptives in 2020, according to the annual report.
The herd was 38% male and 62% female.
The expected range of variation, based on rudimentary statistical formulas with n = 117 and p-bar = .50, is 36% to 64%.
The observed percentages fall within those limits so they could be attributed to chance, the result of a simple random process centered at 50% males / 50% females.
Subject-matter knowledge may suggest otherwise.
