Maybe it's up to your DM to decide if your new form is smart enough to know what you are in fact a druid concentrating on a spell?

But if you are polymorphed whilst Calling Lightning, its unclear whether you can call those bolts down in your new form. So I could see ruling that if you become polymorphed while you are concentrating on Fly, the target of your Fly spell can still fly. A bolt of lightning flashes down from the cloud to that point.' Is a mouse capable of 'choosing a point'? But, let's take Call Lightning as an example - 'When you cast the spell, choose a point you can see under the cloud. E.g., by it's nature, a mouse can't speak a command word, sure. The polymorph spell says = 'The creature is limited in the actions it can perform by the nature of its new form, and it can't speak, cast spells, or take any other action that requires hands or speech.' That by the nature of its new form is doing some heavy lifting. However, if the thing you are concentrating on requires you to take an action to do something with it, can you take that action in your polymorphed form? So if you become polymorphed whilst concentrating on a spell, Sage Advice has said you maintain that concentration.

I imagine this question has already been done to death, but I can't find exactly what I need. Phandelver and Below: The Shattered Obelisk Mordenkainen Presents: Monsters of the Multiverse

Call lightning 5e questions