In 'large herds of elephant and buffalo', why elephant not elephants?

I found the following expression in dictionary.

large herds of elephant and buffalo

A herd must be more than one, why using singular not plural?


Solution 1:

Elephant can be plural, like deer.

See the Merriam-Webster entry for elephant:

el·e·phant noun, often attributive \ˈe-lə-fənt\

plural elephants also elephant

Buffalo also can be plural, like deer (and elephant).

See the Merriam-Webster entry for buffalo:

buf·fa·lo noun, often attributive \ˈbə-fə-ˌlō\

plural buf·fa·lo or buf·fa·loes also buf·fa·los