I went back over chapters 98 - 118 and duly noted every "bird" appearance. This is speculation for speculation's sake, but unless Fuji simply has a boner for birds - these bird appearances may serve a greater purpose to the narrative. That purpose obviously being that Nayuta can borrow the hearing of lesser life forms. Hypothetically, if Nayuta was "present" at each scene: how much would she know?

>Ch. 99.
Birds over school as Asa eats ice cream
>Ch. 100
Birds fly over the school as “Asa” announces wanting to go to find and kill Chainsaw Man, giving “herself” back her body if “they” beat Chainsaw Man
>Ch. 106
Birds fly over the alley as “Asa” talks to herself about killing Yuko at school tomorrow and how her goal is to beat Chainsaw Man. Birds then apparently observe Yuko as she walks to school the following morning.
>Ch. 109
Birds flying over the school as Yuko wrecks havoc
>Ch. 110
Birds soaring over the city as people gossip about Yuko turning into a devil and attacking the school.
>Ch. 111
The birds flying above the area where the False Chainsaw Man slaughters Yuko.
>Ch. 118
The birds flying away just as Yoru attempts to turn Denji into a weapon

It would be interesting if this were the case. She would know Asa is a threat to Denji (even heard her attempt to turn him into a weapon.) She would also know there is a Fake Chainsaw Man on the loose. Anyone think Fuji will deliver, or he just really likes drawing birds?