Common Chiffchaff, Mosquitero común

Description:

It is a migratory passerine which winters in southern and western Europe, southern Asia and north Africa. Greenish-brown above and off-white below, it is named onomatopoeically for its simple chiff-chaff song. It has a number of subspecies, some of which are now treated as full species. The female builds a domed nest on or near the ground, and assumes most of the responsibility for brooding and feeding the chicks, whilst the male has little involvement in nesting, but defends his territory against rivals, and attacks potential predators.

Habitat:

Rocks over Tagus river. Parque nacional de Monfragüe

Notes:

There is a iberian endemism, Phylloscopus ibericus, but it is very difficult to differentiate from P. collybita. The way they sing it is a bit different but this guy was not singing at the moment it was spotted. I identified it as P. collybyta but it is not unrealistic to consider that I could be wrong