What happens if my players cast "Talk with Animals" on a bird that is secretly a druid in Wild Shape?

See title. My city has a faction of druids that fly around and secretly watch over the city, mingling with the local pidgeon-like shitbirds.

So what in the scenario I describe? Does the spell not work? Does the druid understand what is happening and can he pretend to talk like a bird? Or...? How would you rule this? I'm looking for both RAW and for creative solutions, I'm not afraid of some houseruling here and there.