Here's why:
* Common nouns refer to general categories of people, places, or things.
* Proper nouns are specific names for people, places, or things.
"Red panda" describes a type of animal, not a specific individual. It's a common noun just like "dog", "cat", or "bird".
However, if you were referring to a specific red panda with a name, like "Rusty", then "Rusty" would be a proper noun.