If you're willing to go there, you can have the birds spread disease or toxins! As the birds operate differently with their biology, you can do things that make them little to not affected at all.
Why the birds if you have such weapons? The birds have human level intelligence. They can go somewhere and specifically target the enemy. The disease or chemical can then be made to affect only a tiny area/a few persons/one person. That prevents uncontrollable spread, which is one reason you would never want to do biological warfare in normal circumstances.
Alternatively the birds can be very secret. You give them something that can be dropped and fire something deadly at close range, or the biological/chemical attack again. You then just keep killing high ranking officers and politicians with these secret assassins until they are in chaos/give up/change political stance. It is hard to defend against them. Part of the high ranking might go in hiding if a ton of them started dying, but then you'll kill anyone that is still high ranking but not in the bunkers yet.
If you want them as soldiers and not assassins or biological weapons handlers, they likely will be used as support. They can be great spotters. They are incredibly difficult to detect and can relay enemy positions, allowing you to shell it with smart weapons or prepare ambushes. They are perfect for any reconnaissance for people or material that can't normally be detected by radar and the like. Wielding weapons is difficult, but only one shot weapons/bombs in special conditions would really make a difference. Valuable, but maybe not good as a constant tactic.