Hello johnnyblues,
I do not know what the industry standard is but I tip 10% of the whole cost I paid to the Safari company, not counting my air fares, any before and after hotel bills, etc) in US Travelers Checks.
Then over and above that, I like to give special gifts to special people like the trackers, skinners, etc.
Wrist watches, binoculars (Used/Tasco, etc), battery lamps that clip onto a baseball cap, soccer ball, wrist rocket sling shot, T-Shirts/socks/tennis shoes (new, in the package).
For the Laundry Crew, Kitchen Staff and such: fancy scarves (wall-Mart, etc), lapel pins of parrots, or other tropical animals, earrings, necklaces, etc.
Regarding the extra gifts, beware that if you give one staff member a necklace and another a scarf, there will be an argument so, make your choice of gifts to be the same if you can.
Same for the trackers and such.
I usually give the PH a bit extra money or whatever I think he can use, within reason.
Cheers,
Velo Dog.