Hello & welcome, I am Dr. B, a licensed veterinarian and I would like to help you with your wee one today. I do apologize that your question was not answered before. Different experts come online at various times; I just came online, read about your wee one’s situation, and wanted to help.
I must say I am quite concerned about your wee bird, especially if he is showing signs of breathing issues. This heavy breathing suggests that he may not be able to exchange oxygen as well as he normally has been able to do. So, as his breathing is abnormal, it is prudent to have him seen as soon as possible. Because if he is struggling to breath, then this is a red flag of urgency and he may need a local vet (even non-avian since they at least will have oxygen and the basics to treat a bird) to put him on oxygen to stabilize while addressing what is causing his respiratory disease (ie bacteria, fungus, parasitic, nutritional, and viral agents).
Now the reason why his heavy breathing is so important to pay attention to is because the problem I am sure you will appreciate with birds to that they do a very good job of covering up when they are sick. This is because as a prey species, attention to your illness will make you a target for predation. Therefore he is hardwired to pretend he is fine. Still his being quiet (less activity/singing = less oxygen requirement = easier to manage on his compromised respiration) and give us a clue to just how serious this is for him on top of those respiratory signs. So, if we are even seeing him like this then we need to pay attention and address this aggressively before it can become an even more serious issue. Too often we are the last to know when our birds are sick. And too often we only see signs of struggling when their condition is just too advanced for them to hide any longer. Therefore, bird instinct puts us human owners at a disadvantage for catching things early, and makes addressing the signs we are seeing now even more important.
Now you will unfortunately be limited in what you can do at home if there is a problem within his respiratory system. The over the counter treatments are rubbish at best and with respiratory struggles of this nature we do not want to waste precious time for him. So, I will just touch on the nutritional causes for his condition but we'd want him evaluated by his vet to rule out the others I noted above and get him on appropriate treatment before he gets to a point where he cannot breathe.
In regards ***** ***** induced respiratory disease, this is quite often linked to a deficiency in vitamin A. Vitamin A deficiency tends to be characterized by sneezing, wheezing, nasal discharge, crusted or plugged nostrils, lethargy, depression, diarrhea, tail-bobbing, thinness, poor feather color, swollen eyes, ocular discharge, anorexia, gagging, halitosis and a "slimy mouth". This is quite common in pet birds since many diets are imbalanced or many birds will selectively graze and fill up on wrong foods (ie. sunflower seeds). If he is on an imbalanced or all see diet, then you may need to consider converting him to a pellet diet, supplementing his diet with vitamin A or try to tempt him to eat some veggies or fruit. You can try leafy dark greens and vegetables (i.e. kale, squash, celery, carrots, corn), as well as fruits (i.e., bananas, grapes, apples, grapes, pears, etc). They can also have seeding grass, and dandelion (flowers, roots and leaves). So, this is something to keep in mind while ruling out infectious agents and something to address for his long term health.
Otherwise, we would want a local vet to examine him, have a listen of his chest and determine if there is a respiratory infection (and if so, to what extent). Depending on the vet’s exam findings, they will be able to advise you on which causative agent might be present, and guide you on diagnostics and treatment steps to get him well.
Overall, his heavy breathing is a serious concern here that we don't want to leave to linger. If he is struggling to breathe, then we do have to consider having him seen by a vet as soon as possible to get him help and address this respiratory disease. This will give you the best chance of helping him and getting him back to breathing comfortably.
Just to make sure there are no avian vets in reach you aren't aware of, I'd note that these databases may be of use: AAV (http://www.aav.org/search/), Avian web(http://www.beautyofbirds.com/recommendedvets.htm) or Birdsnway(http://www.birdsnways.com/birds/vets.htm).
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