There is a sort of new rash of chicken feeders that works by a feed box being locked up until a chicken jumps on a pedal to unlock it. I've heard many labels but Treadle Feeders seems to be the most commonly used to describe them. They work simply by weight which the chicken supplies by stepping on a pedal step and some kind of door raises up or swings open. I have investigated or reviewed a fair amount of these types. The ones which opens a door straight upwards works with the weight of the chicken essentially is counter-balanced by the actual door which has to defy gravity greatly to raise up. The ones that just open a flat horizontal lid to a gravity fed feed tray, works pretty well if the "lid" only moves up with a down force the same weight as the chicken. The pedal has a few "elbow arms" that transfer the pedal going down with linkage to make the door go up. The weight of the chicken only will make the door open if it completely steps on it. The chicken cannot use it's beak to raise the door up thus neither can mice, rats, birds or anything that weighs less than a chicken. The door raises up and back out of the way. It happens so fast that the chicken doesn't even register it. There is one situation where opening a flat horizontal "lid" up creates a potentially fatal problem. Chickens like to stand in their feed dishes and of course they will be bending over to eat. Once they climb inside the door closes on them possibly trapping them such they don't know enough to open it back up if they are smaller than a full grown hen such as teens or grow-outs. I had one die from that. If you put a chicken in the dark suddenly they go inert and dormant. In most cases other chickens will come and let it out but it still is a serious risk I don't like to play odds with. The solution for that situation is easy. The door needs to be a vertical door (like a roll top desk) and only "raise a window" into the feed tray. The chickens can only put their heads inside to eat while standing on the pedal. You only have to rotate the lid design 90 degrees. The swing door kinds of treadle feeders are probably the worst design of these two types for one simple reason. It takes a couple pounds of chicken to move the pedal down to make the door swing back but a small animal can simply push the door in with little weight and crawl inside. The way it is designed is the door is not the counter weight to the pedal but just set up so that the chicken's weight is needed to make the pedal move independent of the swing door. Another Linkage bridged off that weight and separate counterweight design then only needs a little force to "swing" it in. Most of these types swings back and up in a quarter circle motion. The reason it is very easy to understand in engineering concepts. You can push the door with hardly any weight due to reverse leverage. The pedal to the door ratio is about 8 to 1 but going the other way it is 1 to 8, means a lot of weight is needed to open the door with the pedal but a little weight is needed to push the door to make the pedal go down. The weight factor is neutralized by the separate counterweight. What little weight is on the door only is swinging easily do to the rod it swings from. A little rotation of the rod moves the door a lot. Even putting more weight on the bottom of the door does not change this reverse leverage ratio. A rat with a wedged nose with his quarter pound weight behind him or what extra force he applies using his legs will easily just push the door open (where he will go to first). The funny part is that even if the rat gets trapped, a hungry chicken will come along and set the rat free. Whoever bought that feeder for their chickens will teach their chickens AND the rat how to use it and probably never know it is happening. There is a solution to this issue as well. The pedal needs to have an auxillary linkage that "unlocks" the door initially before the pedal makes the door open. It is a complex solution because of needing to create a delay of opening so the door can be unlocked in the first quarter inch of movement of the pedal. The linkage needs to be attached to the front edge of the pedal and extended back to the door to use the full range of down motion. The pedal is rotating down, not dropping down. There is little movement down where the pedal is close to door. The pedal is a cantilever of length. Such an un-locker linkage would be thrown out of calibration (bent) easily with chickens jumping on the pedal so often. There are two well advertised versions of this type of chicken auto swing feeder out there. i have them both and found the fatal flaw almost right away. I have tried to fix them with small success but I think they are basically useless out in the open as a sure fire preventative to any hungry scavenger getting fed. The pedal moving weight has to be counterbalanced by the door's weight. It should take the same force to move either the pedal or move the door manually. Chickens understand the pedal and learn it. Rats learn the door and use it. Which one is going to empty the tray first?