Thank you all for you comments.
As I said, my first idea was a croaking, and still I think it can be (thick bill, head seems streaked). However, I have to recognize that cisticolas in south africa are very difficult to differentiate (at least for me: too many species and all of them very similar).
Picture was taken at iZindondwe Pan, at the Eastern shores of Isimangaliso. May it is helpful to identify the bird.
Last edited by arodris : Saturday 26th October 2019 at 22:11.