Further to the thread focussing on Willow Warblers and Chiffchaffs with 'combination songs, I'm launching the following as a new thread, as it seems better to give a title with specific ref to ibericus.
Yesterday (April 27th) I encountered yet another Willow Warbler using a 'combination song'. This one again juxtaposed some rapid Chiffchaff-like notes to normal WW song but also gave occasional song phrases very like the usual advertising song of Iberian Chiffchaff. Details have been added to my webpage on mixed singing. Scroll down or hit the bookmark marked to 'Example 4'.