A half a dozen chickens should eat about 50 lb a month in feed.
A lighter weight hen will eat about 1/4 lb of feed per day.
If they eat grass they will eat less feed (free ranging) than if penned. Take all these factors and try to figure your feed consumption - what they should be eating.
My coop with 17 hens in it goes through about 6 lb per day of feed- sometimes a bit less. This is about a horse scoop and a half. Of course the weather is a bit cold now. They will need less in summer also when the forgage is more tempting.
If the feed consumption is way too high then consider rodents. Or squirrels/sparrows.