Again a wonderful and complete article on Identification of Iberian Chiffchaff, is possible to see in Ornithomedia.
With a reference to the post of Birds in the North of Spain on the Song of Iberian Chiffchaff.
“The Iberian Chiffchaff Phylloscopus ibericus was previously referred to erroneously as P. brehmii and until recently was treated as conspecific with P. collybita and P. canariensis; It has been elevated to rank of full species on basis of bioacoustics, morphology and molecular biology.
It breeds in South-western France, Northern and Western Spain, in Portugal and very discontinuously in Southern Spain, Northern Morocco, Northern Algeria and North-western Tunisia; non-breeding range is not well known, includes North-western Africa (principally Tunisia), but main area appears to be farther South, in tropical Western Africa.
Several birds were reported during Mid-April 2010 in French departements (Vendée, Loiret, Indre) situated quite far from the Pyrénées. We present you a list of features to identify this recently-recognized species.”