Decide what animals you want to feature in your documentary, and where. A crew can film a wildlife documentary anywhere. You can find fascinating animals on a prairie in Minnesota as well as in the wilds of Africa. Key in on your favorite fascinating creatures and study the habitat by making trips in your local area, or scout out locations in the Amazon or the Australian outback.
Contact nature organizations if you want to film in exotic locations. Call groups like Afriscreen Films, based in Botswana, for African productions or the International Association of Wildlife Filmmakers for resources on all types of wildlife documentaries.
Secure proper equipment. You'll need cameras for aerial photography if you're filming a wildebeest herd in Africa, or underwater video camera housings if you're filming a documentary about sea life. Some companies offer custom built underwater cameras.
Assemble your production team. Find cameramen, assistants, sound technicians and others with an interest in animals and wildlife in addition to their film production skills. A fearless sense of curiosity helps too, especially if you're filming cobras, lions or other dangerous creatures.
Add post production graphics and titles when you're back in the studio. Contact a post-production house in your area or use software like Apple's Final Cut Studio 2 for smaller projects.