Start with the breathing itself
The earliest signs of respiratory illness in chickens are sounds and small changes you can catch on a quiet morning visit to the coop. A healthy hen breathes silently with her beak closed, so sneezing that repeats through the day, a wet or bubbly discharge at the nostrils, and watery or foamy eyes are your first clues. Listen for a rattle, wheeze or whistle as the bird breathes, and watch for the tail bobbing with each breath, which tells you she is working harder than she should to move air. Head shaking, stretching the neck out to breathe, and breathing with the beak held open all suggest the airways are narrowed or irritated. A swollen face or swollen sinuses around the eyes, and a comb that turns dusky or blue, are later and more serious signs that the bird is struggling.
The changes that show up around the coop
Breathing signs rarely travel alone. A hen who feels unwell in her airways usually goes quiet, stands fluffed in a corner with her eyes half closed, and loses interest in scratching and feeding. Laying hens commonly drop off lay or stop altogether, eggs that do arrive may be thinner-shelled, and the water drinker empties more slowly because the flock is drinking less. Check the droppings too: a bird that is eating less passes less, and any change running alongside the breathing signs is worth noting. Weighing a bird in your hands helps as well, because a hen who has been quietly unwell often feels lighter across the breastbone than she did a week ago.
One bird or the whole flock: why the pattern matters
Whether one chicken is affected or many changes what the signs are likely to mean, and it is the first thing a vet will ask. A single bird with a sneeze may have inhaled dust or a grass seed, or be reacting to ammonia building up in damp litter, while the same signs appearing in bird after bird across a few days point towards something infectious moving through shared air and shared drinkers. Chickens share everything, so a problem that spreads is managed very differently from a problem in one bird. Note which birds show signs, in what order they appeared, and whether any new birds joined the flock recently, because that timeline is genuinely useful evidence.
What you can do today while you watch
Move the worst-affected bird into a separate pen or crate somewhere warm, dry and out of draughts, with her own food and water, so you can watch her closely and slow any spread. Check the coop's ventilation: chickens need fresh air moving above head height, but a draught blowing directly across the roost makes breathing harder, and damp, strong-smelling litter should be forked out and replaced. Offer plain fresh water and tempting feed, and spend ten minutes simply watching the flock at rest, because breathing effort is easiest to judge when the birds are settled rather than stirred up by your arrival. Write down what you see with times attached rather than relying on memory.
The point at which a vet needs to be involved
Breathing problems in chickens can have many different causes, from dusty housing to viral and bacterial infections, and the signs overlap so much that only an examination, and sometimes testing, can sort one from another. Do not wait if a bird is gasping, breathing with her beak wide open, has a blue or purple comb, or cannot be roused to eat and drink; those are same-day calls. Call promptly, too, when several birds develop signs together, when a bird dies unexpectedly, or when a mildly affected hen is no better after a short period of separation and clean air. Keeping those dated observations in KinsLe's Pet Passport means the flock's whole story is in one portable packet when the vet asks what happened, and in what order.