Birds have a tendency to hide sicknesses until it can't any longer. This is a self preservation behavior built in so that when a predator shows up, they don't look like the weaker slower easier meal.
My bird had a respiratory problem due to some work being done on the house. Turns out that the dust, alongside the cold air coming in gave the poor thing pneumonia and we had to take it to a bird hospital for anti-biotics. Bird's back to being fine and singing again as usual.
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-=[ Merlocke ]=-
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