I trust you saw my quick reply earlier today. The bird is a 99% safe Brown Shrike, not an Isabelline. I have looked again at the two photographs and can add also these three characters pointing the Brown Shrike way: (i) narrow tail-feathers, (ii) not a trace of a pale primary patch near primary-coverts, which a young male Isabelline would show in vast majority of cases, and (iii) extensive and strong scalloping of underparts, which is good for Brown but of course shared by a minority of the most marked Isabelline.
But safest Brown Character is that all (at any case longest two) tertials have solidly dark centres with strongly contrasting pale edges. A young Isabelline would have a pattern more like in young Red-backed, with some pale irregular pattern also inside dark subterminal margins. The prominent supercilium in combination with dark 'mask' further supports the identification.