In order to photograph wildlife, you generally need telephoto lenses with a focal length between 300mm and 800mm. These lenses are also heavy, especially when carrying around on foot. The charts and table on this page may help you decide which telephoto lens to buy, if the weight plays a major role.
For more details read my article Canon vs Nikon Telephoto Lenses on photographylife.com
It is kind of frustrating that the Canon lenses are about half to a full kilo lighter (because of the fluorite lenses) than the Nikon ones if you are an owner of Nikon equipment like me. For the weight of a Nikon 500mm you get a Canon 600mm...
Note: The column headings of the table below are sortable. Just click on them.