Originally Posted by
Keravath
In terms of summoning, the Druid specifies how many creatures and what CR they will be as per the spell. The DM can then decide the shape that the spirits take.
However, it is important for the DM to note that, like find familiar, conjure animals and several other “summoning” spells do NOT summon actual creatures of the specific type, the spells conjure fey, fiend or celestial spirits (type chosen by the caster) that take on the form and stat block of the specific species.
There is no requirement that the form of the conjured creature actually exists in the local environment somewhere. The DM has latitude in what form the spirits take because it is possible that the game world doesn’t contain all possible beasts, fey or other forms. However, whether or not the creature exists locally is not a requirement for the spell or what forms the spirits take.