Well, there are several things here that are not being told and one is that ball pythons are a ground dwelling species for the most part and they are very secretive. They certainly are at home in a termite mound, burrow , or hole until they defecate inside of it or shed their skin and sense that they may be detected by their prey and then they venture out seeking a new place to set up camp. They climb if they have to, but are more comfortable and secure in the confines of a tunnel, excavated area, depression in the ground or even under rocks. As far as the birds are concerned, what these articles aren't stating is that there are quite a few ground dwelling birds, birds that make their nests in the ground and also underground. Most birds, even if they are airborne come to the ground in search of seeds and insects and generally to feed and its probably then that they become vulnerable to the attack of a ball python. Ball pythons are a very thigmotactic species and seek out the comfort and mainly the security of tight fitting spaces. If they are climbing its a in transit to their next secure spot and if they encounter a meal on their travelling mode you know how opportunistic they are. Justin Kobylka chronicles their behavior and has written about this in his travels to Benin, Ghana Africa in the past.