Hello & welcome, I am Dr. B, a licensed veterinarian and I would like to help you with your wee ones today. My apologies that your question wasn't answered before (I suspect the system had a glitch since the question only appeared to me just now).
Now if your birds are appearing to vocalize or yawn without a sound, I would be concerned that they may actually be gaping to try to clear their throats and get a good breath. If you can post a video of what they are doing, I'd be happy to have a peek at what they are doing. Still in the meantime, to just to give you an example of what I suspect you are seeing you can peek at an example HERE.
Now as you will see from the video's title, we do have at least one differential to consider and address here. That said, we do have others to consider (which I will touch on in a moment). But before I do so, I do want to note that having multiple birds does raise concerns for infectious disease differentials here. Therefore, first thing, is to isolate these affected birds from the others and make sure they are not able to spread this infectious agent into the communal airspace (because airborne pathogens can spread within the airspace quite easily)
Now when birds demonstrate respiratory signs of this nature, we do have a range of agents to consider. This includes Infectious Coryza, Acute Fowl Cholera (Pasteurella multocida), Influenza, ILT IRT, infectious bronchitis, Chlamydiosis, and mycoplasma (Mycoplasma gallisepticum). Furthermore, we can see localized throat based disease due to Trichomoniasis (canker), Fowl pox (wet form causes canker lesions in the throat) and Syngamus trachea (gape worm) infestations. So, there are a number of issues that could cause this as a early stage signs.
Therefore, if you are comfortable handling your birds, then you can potentially narrow down a few of these differentials at home. If you are comfortable doing so, then one at a time, you may consider having a peek down her throat to rule out you gapeworms. If you look down the throat, you may be able to see them or one of the other causative agents (ie the plaques of Fowl Pox or discharge of canker). If you can't see anything, since you can only look down a chicken throat so far, then you can try the "Q-tip test". To do this, you need to place the bird in your lap, gently open her beak, and swab a Q-tip down her throat (twirl it as you do this). Twirl as you bring it back up, and if she's got gapeworm, you'll see thin, red strings on the q-tip. This way you will know if this is the cause. But if you end up with a cheesy discharge then canker or pox would be higher on the differential list. If there is any other discharge, the bacterial causes would be suspect. And once you have identified what is present, you will be in a better position to know if you are treating them appropriately.
As well or alternatively, you can start treating them to rule out potential suspect (not ideal since you will be treating in the dark but an option). First, if the birds have not been wormed, then you could consider worming them all at this stage to ensure parasitic differentials are addressed and ruled out. Make sure to use a good quality wormer that will address gapeworms (ie Flubenvet).
If you prefer to know what is present before broad spectrum worming, you can consider pooling fecal samples from affected birds and submitting this sample to your vet to analyze. Or if you are keen and have a microscope, some owners do check fecal samples themselves, and this may be an option for you to see if there is any sign of gape worm (or other worms) eggs to help you diagnose or rule out the gape worms. You can find a good Fecal Sample Evaluation Guide here. Depending on the findings here, you will be able to treat appropriately. And if the sample is free of eggs, then you can focus on the other potential causes for their signs.
Otherwise, for further measures to pinpoint the causative agent and increase your treatment success, you do want to consider involving your vet. They can listen to their lungs, examine their airway, and help you determine the disease focus and therefore rule out some of these agents. Furthermore together you can collect some respiratory secretions from one of the birds to be cultured. This will tell you what agents are present and what treatment will actually clear them.
Furthermore, once you have samples for culture, you can consider a broad spectrum treatment to try and tackle as many of the bacterial causes as possible. There are a range of options that would include, erythromycin, oxytetracycline, or macrolides. Other options may be tilmicosin, tylosin, spiramycin, or fluoroquinolones (especially useful if Mycoplasma is suspected).
Further to this, supportive care will be a key facet that we need to make sure to address. It does sound like these birds are early stage (but chickens are tricky since they will fake like all is well until disease is too advanced to hide), but once you have them isolated you do want to keep a close eye on them. If there is any appetite or drinking decline, they may need your assistance. Or if you think they sound congested, then you can consider using a bit of steam treatment (either in steamy bathroom or if you make a steam tent with a cat carrier + humidifier under a thin bed sheet). How intensive your supportive care will need to be will depend on how severely the birds are affected but hopefully as you sound to have picked this up early, it can just be nipped in the bed and settled before you have a flock outbreak.
Overall, silent squawking/yawning tends to be a hint of respiratory disease arising. That said, it isn't specific for what kind is afoot. Therefore, you do want to take some of the above diagnostic steps to narrow down causes and avoid having to treat for everything. Otherwise, you can consider supportive care, worming and covering them with a broad spectrum antibiotic to start; but the sooner we know what is behind their signs, the sooner you can address it effectively and economically and take steps to protect the flock.
I hope this information is helpful.
If you need any additional information, do not hesitate to ask!
All the best,
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