My birds are eating about a quarter to a third less of their feed than normal right now thanks to free-ranging, so it is a possibility! You have to keep in mind, though, that the area they free-range over matters a lot when it comes to how much forage they can get off of it. Here, my birds range through a mixed wooded area with lots of different species of greens to peck at, shed leaves to dig through, low wet areas with lots of bugs to hunt, etc. If free-ranged on a trimmed lawn of just grass and not much else, they aren't going to pick up nearly as much forage.