So... it's about that time of year when all chickens try to give their owners a minor heart attack.
It might go something like this:
You sleepily wander out to the coop one morning in late summer/early fall, expecting to do your usual check-in/feeding/watering and you open the coop to find feathers EVERYWHERE! You immediately panic and start doing The Count to see who's ok and who got attacked by some vicious creature and find...
Everyone present and accounted for.
You count again... and again find everyone to be utterly hale.
(And looking at you very curiously because they're not quite sure why you're freaking out.)
Now that you can breathe normally again, you may notice that all the feathers seem to be from a particular bird or two and, upon closer inspection, you see that they seem to be wearing a lighter-season jacket than usual (they're not quite as thick-and-fluffy).
This, my feather-loving friends, is what's called MOLTING. It happens approximately once a year, when all birds gradually shed their year-old, worn-out feathers and replace them with shiny new ones (check those two links for pics of slightly less-gradual molts). In your typical migratory wild birds, this happens so they have fresh, strong feathers to carry them the thousands of miles they need to travel to get to their wintering grounds. In non-migratory birds, it happens so they have fresh, complete, un-worn feathers to create efficient insulation and keep them warm for the winter. In chickens, it happens so we have a treasure trove of feathers with which to make ART, of course. (Except that many of them will be worn/broken/messy/otherwise unusable, in which case they're just there for the initial scare-factor.)
Ponder this: in nature, many physical structures are intended to be temporary. Bird nests are only made to last a season, feathers break down over the year and get replaced, plants grow entire structures that only last a few months, we all continuously shed-and-replace hair, skin, the cells in our stomach lining, etc. And all of this "waste" becomes "fuel" or "materials" for something else to eat or use. The cycle of breakdown and regrowth is necessary and efficient. Let the cycle happen and let things go.
~~End philosophical interlude~~
There are other not-so-okay reasons that one of your girls might lose feathers, including external parasites or disease, or if they are getting picked on by other members of the flock. Generally they will lose feathers in a sequence starting with the head and neck, then progressing to sections of the body, and finally ending with the wings and tail. If instead of this pattern you are noticing loss of feathers only around the vent or chin check for lice and mites, if the missing feathers are only on the top of the head/neck check for aggressive flockmates, and if there are any other accompanying symptoms such as lethargy or lack of appetite or a general case of NQR (Not Quite Right) then you likely have an issue that is somewhat unrelated to molting.
In general, you don't need to change anything about your daily routine to accommodate the molting process, but given that they will be putting a lot of their body's resources into growing new feathers they tend to lay less frequently during this time. If you'd like to help support their systems during the process, you can either switch to a higher-protein food, or supplement your regular food with high-protein fats, oils, bugs, etc. in the form of higher-protein commercial feeds, sunflower seeds, mealworms, yogurt, or cooked egg and meats. Here's a great BYC thread with more info on feeding for molting and a brief post (not mine) about the fact that chickens are not vegetarian.
I'll leave you with a not-so-minor aside...
If part of the reason you are keeping or want to keep your own chickens is to do some small part to remove yourself and your family from our current large-scale commercial food system, then GREAT! Kudos.
If you hadn't considered this aspect before, then here's one of a gabillion reasons that growing crops and raising food animals on an industrial scale just isn't working: it is a common practice in the commercial egg production industry to induce forced molting in the entire operation at once by withdrawing food for a week or more.
From the linked article, "Natural molting is stimulated by shortening day lengths combined with
stress (of any kind). Before confinement housing with artificial lights
were the norm, the fall molt caused a fall scarcity of eggs and high
market prices. Farmers attempted to pamper their flocks to prevent the
molt as long as possible, to take advantage of the high prices. Modern
controlled-environment confinement housing has the opposite problem; the
hens are not normally presented with sufficient stress or cues to go
into molt on their own. However, after laying continuously for nearly a
year, their rate of egg production declines, as does the quality of the eggshell and the egg contents. In addition, the hens are seriously overweight."
So yes, the reasoning for it is understandable, but that's only once you get past the precursor that "modern controlled-environment housing... [doesn't present hens] with sufficient stress or cues to go into molt on their own". In my opinion, THAT's the cause. We've been trying to take the "natural" out of nature so we can control it. Forced molting is simply treating a symptom of the system, when it's the system itself that's flawed.*
(And if this is true for them, can you imagine what our own controlled-environment housing is doing to us? Get outside. Eat seasonally. Move your body. Get dirty.)
Next up... To light or not to light: prep for winter.
*This opinion is addressed in the "Critiques" section of the article, where it says that the practice of controlling the molting process predates the development of an industrial egg production system. Sure, but you're still trying to control a system (nature) that took eons to develop, just so a very few people can produce eggs (that they're barely getting paid for) for everyone else to have every morning without seasonal interruption. The technology is useful and wonderous, but we've swung the pendulum too far.