There were 21 males and 57 females in the herd this month, according to a report posted today by WMDT-47 in Salisbury, MD. Sounds about right, what’s the problem?
Well, the proportion of males seems low. Alternatively, the proportion of females seems high.
The expected proportion of males is .50. Ditto for females. But those are properties of herds that are indefinitely large.
For herds of 78 animals, the observed proportions should fall within calculated limits, namely, .50 plus or minus an amount attributable to random variation.
Using p-chart limits, with n = 78 and p = .5, the proportion of males (or females) in the herd should fall between .33 and .67. The observed proportion of males is 21 / 78 = .27, which is assignably low. The observed proportion of females is 57 / 78 = .73, which is assignably high.
What is happening to the Assateague ponies? A special cause should be sought.
Bands of free-roaming stallions might be bad for tourism so maybe they are the subject of an outplacement program.
Could it be that the fertility control program is screwing up the herd by interfering with natural breeding patterns? Why would mortality favor males?
What might this portend for other herds where PZP is administered?