Spotting

No Common Starlings in Portugal in summer, only the Spotless Starling.
Black Redstarts have prominent red sides to a straight tail.
This is almost certainly a very young Blackbird as it has a large partly fanned tail and a clear gape line.
Starlings have much shorter tails.

I'm positive this is not a young starling. They are paler, have smaller heads and less proportionate eyes. Their bills are longer and thinner. Plus, they normally have white throats.
That said, I'm not experienced with juvenile Portugal birds, so I can't say what this is, but being all too familiar with starlings, I can say that this is not one.

I think the bill and color of it are right for a starling, if you search juvenile black birds you will see that they are more brown with streaks on the chest.

Bill shape and overall coloration are wrong for juvie Starling here. Not 100% sure what this individual is, but I'm thinking maybe a juvenile Common Blackbird.

When they are young they are all grey, i have rehabilitated tons of them here's a link to one of my photos :) in your photo it's much younger thank mine :)
http://www.projectnoah.org/spottings/661...