The collective noun for a group of jaguars is "jamboree". The word "shadow" has also been identified to be in use when calling a group of these animals.
Jaguars are the largest of South America's big cats. They once roamed from the southern tip of that continent north to the region surrounding the U.S.-Mexico border. Today significant numbers of jaguars are found only in remote regions of South and Central America—particularly in the Amazon Basin.
These beautiful and powerful beasts were prominent in ancient Native American cultures. In some traditions the Jaguar God of the Night was the formidable lord of the underworld. The name jaguar is derived from the Native American word yaguar, which means "he who kills with one leap." - National Geographic
Check out more collective nouns for the big cat species on animalsandenglish.com and bigcats3.tripod.com.