This year’s survey of our subway stations by the Straphangers Campaign showed a 3 percent drop in rats observed. One reason might be a new-for-2013 weapon in the rodent war: birth control. Working with the company SenesTech on a research project, the MTA introduced ContraPest, a bait that gradually leaves the females sterile. Official analysis hasn’t been released yet, but “anecdotally, it definitely has been successful,” says the MTA’s Kevin Ortiz.