The picture here shows an old Miller fluid head on wooden legs. Used and abused by students at Newport Film School, the head leaked grey grease and the legs jammed when they were wet. For wildlife cameraman work with long lenses it was rubbish, but when all you have is rubbish you make do. Tripod heads have moved on somewhat.
This link to Tripod Heads will open a pdf of an excellent document by wildlife cameraman Steve Phillips. Steve is well known for not only being an excellent cameraman, but for his extensive knowledge of filming equipment, particularly when it relates to filming wildlife. There is no substitute for testing equipment yourself, and when your own particular usage is as demanding as following small, erratically moving creatures on a 600mm (or more) lens, you need to know you have the best kit for the job. Steve has field tested just about all of the practical long lens heads and shares his experiences of using them here.
For any wildlife cameraperson (camera person), this is essential reading whether you’re hiring or buying.