Thank you (and 'your source') so much for the extensive explanation. Very interesting information about the behaviour of these beautiful birds. This was the first time we saw more than one Bateleur in one place. Other sightings were always individuals and most of them adults. Next time we spot one we will look closely and see if we can find more of them in the area and observe their behaviour.
Since I'm Dutch I have no problem reading Afrikaans. For the non-afrikaans/dutch speaking forumites who are also interested, I've translated it in English:
The three subadult Bateleurs, seen together in one tree, are interesting. The Bateleur is an inter-Africa vagrant until it reaches adulthood at about seven years. During this period they migrate across the continent to places where food sources are available at a certain moment. In this way large numbers of these vagrant (mostly subadult) Bateleurs are seen in the southern Kalahari from time to time, mostly in late summer and dry wintermonth. For instance, 30 Bateleurs, most of which were subadults, have been spotted at a natural waterhole near Jan se Draai in the winter of 1992. On 1 july 1988 I counted 66 individual Bateleurs from Nossob to Twee Rivieren. Most of them were juvenile birds but there were also quite some adult birds. In 1989 two adult Cream-backed Bateleurs were shortly seen in the Nossob camp area. They then disappeared again. None of the 13 resident pairs of Bateleurs I've studied had such a white back. Since all chicks have been colour ringed these juvenile birds must have come from elsewhere. Without exception Bateleurs have been breading in the Camel Thorn trees along the Nossob and Auob. I have never found any pairs in the dunes. So these juvenile birds could not have been of any pair in the surrounding area, but must have come from elsewhere.
In Zimbabwe it has been noticed by Carl Vernon that concentrations of mostly subadult birds sometimes occurred at certain locations. Carl has speculated that these concentrations occurred in areas with a sudden local abundance of food in areas which are normally unsuitable habitat for Bateleurs (like in the Kalahari). Concentrations of Bateleurs have also been seen in other parts of Africa like Zambia, Kenya and Kruger National Park. It has also been noted that recorded numbers of Bateleurs have peaked at different times and different places, indicating long distance migrations (vagrancy).
Long story. But to return to the tourist's observation, the juvenile birds that have been spotted together could have been part of such a concentration, or just juvenile birds of the almost 500 breeding pairs (according to Watson, I think there are fewer pairs) in the Kruger National Park, that gathered near a food or water source. The behaviour of one Bateleur attacking the other could have been aggression at a food soure. I've seen such aggression between young Bateleurs at a carcass. (Bateleurs can also eat termites flying in large numbers after a rainshower. They walk on the ground near the opening of the termite nest picking up the termites).
Thanks again Jannie, for your help
(I have more questions about observed animal behaviour for you, both from Kruger and Kgalagdi, but will leave it for later. Don't want to 'overload' you