If a wild budgie catches a cold then what will it do to try and heal itself? There has got to be some other trick rather than getting antibiodics?

Umm well if its a healthy budgie with a strong immune system it will naturally fight it, if not it may die. That's what natural selection is all about. In WA many of the herbivorous native animals are naturally immune to the chemical used in 1080 (fox bait) because over there it occurs naturally in many of the native plants and they have evolved to tolerate it. Animals from this side of Aus aren't able to tolerate it and would be poisoned if they ate those plants.