Here is my estimate on your feed use per day if it was just chickens eating. You have 24 birds, bump it up to 26 due to the two ducks, a quarter pound of feed per day per hen or 6.5 pounds per day for all 24 (26)birds. Twenty days of feeding would be 130 pounds of feed. Twenty five days of feeding would be 162.5 pounds of feed.
Someone already mentioned ten pounds per day is what you are feeding so something is stealing 3.5 pounds of feed or 70 pounds in 20 days or 85.7 pounds every 25 days.
Now, you have freshly dug holes showing up. Someone already pointed out the variety of vermin that dig holes into coop and you mentioned there are no chickens missing. That leaves out the smaller predators and suggests rats doing the digging. And most likely stealing the feed.
I assume you don't have a lot of wild birds getting into the coop? Very nice coop BTW.
Figure 105 pounds of feed loss per month x the cost per bag, and most of us are glad you are now feeding only a commercial ration, and that is your cost per month for not dealing with the feed theft. I'd guess in two to three months you would more than pay for a decent treadle feeder plus prevent a lot of disease and pests from coming into your coop.
From your picture none of the feeders are rodent proof. And the wasted feed is from feed being raked out by hens searching for goodies. If you recently switched from grains mixed with pellets the hens will keep searching for a month or two out of habit.
You don't have to go with a treadle feeder but it is the most efficient way to stop the feed theft. And make sure it is a treadle feeder with an inner lip, at least 1/2" wide projecting into the feed bin to stop most feed raking. The feed should set one to two inches below the top of the feeder front/feed lip, if too much feed is flowing down it will over fill and even the feed lip doesn't help. Make sure the treadle feeder has an optional feeder lip extension to raise the front of the feeder, rarely needed, 95% of hens will stop spilling feed with the normal feeder lip.
There are three main methods to deal with rodents, assuming you have mostly medium to large hens and only a few bantams if any and don't have poults or chicks in the same coop. If you do have some smaller hens they will learn to eat when the larger hens eat but be sure and block off the side of the feeder with gallon jugs of dirt to force them to come in from the front. But never, never, use treadle feeders with poults or chicks.
The first method of stopping vermin from stealing feed is sanitation. Bulk feed in steel barrels with tight lids, the coop feed in a proper rat proof chicken feeder, and clear up the paths that the rodents use to get to and from the coop to their burrows. That forces them out in the open so natural predators can thin out the population.
What is a proper rat proof chicken feeder? It is a treadle feeder, inward swinging door, spring loaded door to prevent rats from just pushing the door open (nearly all treadle feeders do NOT have this feature, only one that I am aware of), a distant and narrow treadle, not a wide treadle step, you want the rodents far enough away they cannot reach the feed if they overwhelm the treadle. And no plastic parts or wood parts other than maybe a treadle step. You will find only two or three treadle feeders that meet most of the specifications, all but one have to be imported, and only one treadle feeder that meets all of the needed specifications. Pay close attention to the negative reviews on all products, most people buy a chicken feeder not because they have rats. The rats and more so the squirrels really test the performance of a feeder and without those springs pre loading the door it is impossible to keep rats or squirrels out of a feeder.
Once you lock the vermin out of the feed the colony will collapse within days unless there is another man made food source or unless you are feeding scraps to the chickens and walking away before the scraps are eaten.
The second method is exclusion, building a Ft Knox coop. Hardware cloth has already been mentioned and the removal of the concrete, rats can chew through concrete. This would cost a fortune with your coop but it will work if you have small breeds of birds or mix poults and feathered out chicks which shouldn't have access to any treadle feeder. Or consider putting these smaller birds in their own small hardware enclosed coop.
The third method is elimination; trapping, shooting, and poisoning. Short term it can help until the rodents wise up to the traps and poisons. But it never works for long term and requires constant work and expense if you use poison. However, the traps and poisons can be effective IF you have done the sanitation process, with them locked out of their normal food they will be come desperate and be more likely to take the baits. Risks with poison are domestic animals being secondary poisoned or the natural predators being poisoned. IF you could clean out a rat colony and didn't do the sanitation work, a new population would find the empty territory eventually and you are back to losing feed.
Good luck with getting this under control.
