Sounds like one of the upper respiratory diseases . Mycoplasma gallisepticum and even infectious bronchitis will cause symptoms like sinus infection , swollen eyes and rattling when they breath. Have you introduced new birds recently ?
http://edis.ifas.ufl.edu/ps044
Either way the treatment is pretty much the same , 5 days of erythromycin or gentamicin , if you can find some.
Thanks will try to source.
First fatality. One buttercup dead when I got home. I was worried the young ones wouldn't be strong enough.
Yes I have introduced birds. They were quarantined for 6weeks. Do you know the incubation period?
Edited to add: I just checked and the antibiotic I ordered today will treat it. Vetafarm triple C. It will be available to collect at 2pm.
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