* Kiwis is the more common and general plural form, referring to multiple birds of the species *Apteryx*.
* Kiwi can also be used as a plural, especially when referring to the fruit, *Actinidia deliciosa*. This is more common in contexts where the word "kiwi" is used as a shorthand for "kiwi fruit."
Ultimately, the correct spelling depends on the context and the intended meaning.