Question

Do we say mode of nutrition in herbivores to be herbivorous or herbivore?

Answer 1

Both are correct, as long as the organism in question consumes plants, it is herbivorous or a herbivore.

Explanation:

A herbivore or herbivorous organism, is an organism which gets its prime nutrition from the consumption of plants.

https://en.wikipedia.org/wiki/Cattle
An example of a organism which is herbivorous or a herbivore is a cow

If an organism gets nutrition from plants life and animal life, it is what we call an omnivore or omnivorous.
https://en.wikipedia.org/wiki/Chimpanzee
An example of a organism which is omnivorous or an omnivore is a chimpanzee

If an organism gets its prime nutrition from the consumption of animal life, it is what we call a carnivore or carnivorous.
https://en.wikipedia.org/wiki/Barracuda
An example of a organism which is carnivorous or a carnivore is a barracuda

Hope this helps!
-Charlie