Note marked undertail-coverts, like in Eastern Orphean Warbler. Shown and pointed out as unmarked in Svensson’s, Mullarney’s and Zetterström’s good field guide.

Geir, on many pictures of Arabian warbler (including Birds of Israel and Lars's and Hadoram's WP handbook), some Arabian warblers do show some markings on the undertail coverts. I am sure that this is a 100% safe identification clincher.

Furthermore, the undertail pattern of this bird, as well as the very short primary projection on this bird (and those on the other two pictures) are good pointers for Arabian warbler and do not suggest (Easter) Orphean warbler.

Geir is pointing out that the Svensson guide mistakenly shows the undertail coverts of Arabian Warbler as unmarked (which is highlighted in the picture in the book).

He uses this and other photos as examples that the undertail coverts actually are marked.

Well, on many pictures of Arabian warbler, the undertail-coverts are (or seem) unmarked. It is simply a variable character. Curious to learn why Killian included this pointer!

Point taken by Jan Hein. My criticism was to Svensson et al. and not the ID of the bird in the picture. I noted this character in Oman in 2005 and told Lars and Dan about it. They were, however, not keen to change text nor painting.