I'm so sorry this is happening, but yes, it does sound like he is going to die without medical intervention immediately. You need to get him to the nearest 24/7 animal hospital (depending on where you are in the world, it's Sunday in the US right now so all Vets are typically closed except for the 24/7 hospitals)...He needs to be put into an Incubator at a hospital that will provide him pure Oxygen and heat, while they try to figure out what is going on with him...
****You need to separate your other bird (who I'm assuming is not acting like he/she is sick as well, correct?) into a totally different room than the sick bird right away. I would put the sick bird into a small box or a small cage/travel carrier, line it with folded towels, and if you have an electric heating pad you need to put in underneath the box/carrier/cage and put it on low/medium to keep him warm and quiet, and totally separate from any other birds, in a different room behind a shut door...
You'll also need to completely disinfect the Aviary, because if the sick bird has an infectious disease or infection, you need to do everything you can to protect your other bird from also becoming sick. You'll have to use some type of disinfectant to soak all of the bowls/dishes and plastic toys/perches, basically everything inside of the Aviary that is NOT WOODEN in, along with scrubbing down the entire Aviary, including the walls, bars, floor, etc., then rinse it very well until you can no longer smell Bleach, then do not put your healthy bird back inside until it's dry...THROW AWAY ANY AND ALL ITEMS IN THE AVIARY MADE OF WOOD OR ANY OTHER POROUS MATERIAL LIKE WOOD, STONE/ROCK, ETC. So you need to just throw away any toys, perches, etc. that are made of wood or stone, along with all Cuttlebones, Mineral Blocks, and any food/treats, etc. Do not try to disinfect any toys or perches or anything else that are made of wood or stone, as bacteria, fungi, parasites, and Viruses will continue to live inside the wood or stone even if you attempt to soak them in Bleach. Just be safe and pitch them...
***Did your bird just suddenly start acting like this, like he/she was totally fine one minute and then like this the next? Or has he/she been acting like they may be sick prior to today? The reason I'm asking is that the symptoms you're describing, if they just suddenly started out of nowhere, sound like it may be due to some type of toxicity or poisoning....Is there anything that your bird could have eaten that would be potentially poisonous, such as plants, insects, household cleaners/chemicals, or any new foods you fed her right before this started? Were you cooking with pots/pans/bakeware right before your bird became sick? Or were you using any small appliances inside of your house (anywhere inside of your house, even if far away from the Aviary) just before he/she started acting this way? Any new small appliances at all in your household, such as any kitchen appliances (griddles, George Foreman Grill, Toasters, Ovens, self-cleaning Oven setting, etc.), or hair dryers, space heaters, air purifiers, etc.?
I'm so sorry, it doesn't sound good, but you need to do everything you can to prevent this from happening to your other bird as well...
