ArlNow.com reports it's part of a regional bunny boom:
“It is indeed a boom year for rabbits in the county,” [Arlington County Parks spokesman Nathan] Spillman said, “Rabbit populations here are cyclical and about every seven or eight years you see a large spike in the population followed by a relatively steep (and quick) decrease as the boom attracts predators like foxes and hawks which bring the population down… It’s likely the decline will start to become noticeable as early as this November.”
According to a just-released inventory of wildlife in Arlington (PDF), the rabbit population in Arlington (made up mostly of Eastern Cottontails, pictured) typically moves in cycles with the population of its primary predator, the fox.And they're quite accustomed to people. The photo above was the second one I took - the first one I accidentally had the flash on. The bunny in the foreground didn't run away at the flash, just perked up its ears for a minute, then went back to munching clover.