What are the signs and symptoms of bird flu in chickens?

[Lawrence]

Infection causes a wide spectrum of symptoms in birds, ranging from
mild illness to a highly contagious and rapidly fatal disease resulting
in severe epidemics.

Decrease in activity
Drastic decline in egg production
Facial swelling with swollen and bluish-violet colored combs and
wattles
Hemorrhages on internal membrane surfaces
Virus isolation needed for definitive diagnosis
Gasping for breath
Muscle
Weakness/paralysis
Diarrhea
Sudden deaths (mortality that can reach 100%)