Choose the black ones
Yes, chickens can eat sunflower seeds, and the bag to reach for is black oil sunflower seed — the small, dark seed sold for wild birds. Its shell is thin enough for a hen to crack without effort, and the kernel inside is oil-rich, which is precisely what makes the seed both valuable and rationed. The big striped seeds in their woody shells are harder work and less rewarding per peck; hens manage them, but black oil seed is the flock-keeper's standard for good reason.
Oil, feathers and the moult
The oil in a sunflower kernel is the point of the treat. Feathers are built and maintained in a world of fats and oils, and a modest sunflower ration through the autumn moult supports a flock growing its new coat — keepers have sworn by a handful of black oil seed in moult season for as long as there have been backyard hens. The same richness shows up in body condition, which is the caution wrapped inside the benefit: sunflower seeds are among the most calorie-dense items on the treat list, and a flock poured seeds daily will fatten quietly while its egg output thins.
Portions you can see
Scatter, do not pour. A tablespoon or two of seed per hen, thrown wide across the run floor, turns a calorie-dense treat into ten minutes of scratching and searching; the same amount in a dish is gone in seconds and mostly into the boldest two birds. Shelled sunflower hearts are fine too and suit bantams and older hens whose beaks are less forceful, but hearts concentrate the calories further, so the handful shrinks accordingly. Seeds belong in the day's treat budget alongside everything else rich the flock gets — mealworms and sunflower seeds on the same afternoon is a feast, not a routine.
Storage decides safety
Sunflower seed keeps well in a cool, dry, sealed bin — and badly almost everywhere else. Damp seed moulds, and mouldy oilseed is genuinely dangerous: the toxins produced by moulds on stored grains and seeds hit birds quickly and hard, and there is no version of blowing the dust off that makes a musty bag safe. Buy seed that smells sweet and nutty, store it off the ground away from condensation, and bin any bag that smells musty, shows webbing, or has been got at by mice. Cheap is no saving if the flock pays for it.
A working treat, not just a snack
Sunflower seeds earn a final role: they are heavy for their size and hens know the sound of them, which makes a small tin of seed an excellent recall lure and a handy reward when you are teaching a new rescue hen that people predict good things. Used that way — tiny amounts, high value — a bag lasts the season.
Because sunflower seed is potent stuff, it rewards planning: the moult-season boost and the daily scatter both belong on the record in KinsLe's Care Teams, so the flock's richest treat stays measured whoever is feeding.