From the Canon Digital Learning Center:
Using two or more Canon Speedlites is a tremendously effective way to make exquisite wildlife images. My journey in wildlife photography began with multiple Speedlites four decades ago. The key is setting the exposure, placing the lights for the best lighting, and getting them to all fire instantly.Read the entire article on the Canon Digital Learning Center.In the beginning, I wired photoelectric triggering devices to each flash, and then advanced to using PC sync cords to wire all the Speedlites and camera together. Both systems were fraught with problems. Then optical wireless systems became available and things improved considerably. And with the new radio controls, it is the best time for working with multiple Speedlites. It is so easy today with modern flash gear, so I hope you will take advantage of it.
B&H carries Canon Speedlite Flashes.