As is my habit when I encounter something new, I did a little research after seeing the jackrabbit a few days ago. What I found out is, as usual, interesting (at least to me!).
First of all, finding one in an overgrazed pasture is not unusual at all. They like shorter grasses that they can see over, since they are preyed upon by a wide variety of raptors and by a few mammals. What I haven't been able to find out is how common they currently are in Sedgwick County. Prairiewolf says he used to see them when he was quite young, but that by the time he was in high school, they seemed to have disappeared from the area. This was the first one he had seen in Sedgwick County since his childhood.
The species we saw was the black-tailed jackrabbit, Lepus californicus melanotis. It's actually a hare, and its young are precocial, meaning they are born fully furred, with their eyes open and ready to leave the nest shortly after birth.
Jackrabbits became a major agricultural pest during the Dust Bowl days of the 1930's. At a time when there was little vegetation at all because of drought, their numbers actually peaked, probably because of warm winter weather and subsequent low mortality. The attitude of "kill any predator you see on sight," prevalent at the time, certainly wouldn't have helped much either. The jackrabbits literally started competing with cattle and other livestock for what little grass was available. (One site, the Internet Center for Wildlife Damage Management, states that hares can eat 1/2 - 1 pound of green vegetation every day, so you can see that large numbers of jackrabbits would definitely have an effect on vegetation.) Jackrabbit roundups were held to try to decrease their population, but these were of limited success. Their numbers seemed to decline naturally over the years, with a particularly sharp decline occurring in the late 50's/early 60's.
While I was unable to find definitive statistics about their current abundance in Sedgwick County, the concensus seems to be that recent changes in farming practices have decreased their numbers overall, especially in eastern Kansas. There seems to be little concern about jackrabbits reaching agricultural pest status again any time soon.
So I think I can enjoy my jackrabbit sighting with little or no concern...knock on wood!