Bird that sounds like a frog? (Video)

I’ve been hearing this “ribbeting” sound from various trees around my garden, I don’t think it’s anything rare but I’m not sure what it is!

I live in South Wales, so along with the typical garden birds (tits, sparrows, finches etc), I also get plenty of Nuthatches, Woodpeckers, Dippers in the river behind my house, Kites (pretty sure they’re not the culprit!) and a pair of Mandarin Ducks that have recently appeared.