Ya if they're set on calling animal control then just call them and be done with it.Do not talk to him. Do not offer to buy the birds. If you do he will know you are the one who called Animal Control. If you let Animal Control handle it they will not only take the animals, they will probably do follow ups to make sure he doesn't get any new birds. If necessary, they will take him to court and a judge can forbid him from owning any pets/livestock.
I don't really know the situation but if those D Uccles are the worst case then idk if that's grounds for neglect or abuse.
Idk I guess I'm old school and still believe in getting some facts before calling in the authorities. The birds are crowded but don't look in horrible shape or anything.