"Bird" has added the numeral 1 to his name. There is a certain commonality to be found in gang nicknames and apparently there was more than one "Bird" within the Florencia gang, thus the footnote style identifier.
In any event, "Bird1" was obviously very talented at what he did and he did a lot of it. His work was so prolific and spread over such a vast geographic area that he could be considered one of the original taggers. This piece appears to be marker rather than spray paint and is dated "'71".