 Birds from Fair Isle , St Kilda and the Outer Hebrides are intermediate in size between S. v. zetlandicus and the nominate form , and their subspecies placement varies according to the authority . The dark juveniles typical of these island forms are occasionally found in mainland Scotland and elsewhere , indicating some gene flow from faroensis or zetlandicus , subspecies formerly considered to be isolated . 
 Birds from Fair Isle , St Kilda and the Outer Hebrides <a href='drop_aux' title='1'><mark>are</mark></a>intermediate in size between S. v. zetlandicus and the nominate form , and their subspecies placement varies according to the authority . The dark juveniles typical of these island forms are occasionally found in mainland Scotland and elsewhere , indicating some gene flow from faroensis or zetlandicus , subspecies formerly considered to be isolated . 
Birds from Fair Isle , St Kilda and da Outer Hebrides intermediate in size between S. v. zetlandicus and the nominate form , and their subspecies placement varies according to the authority . The dark juveniles typical of these island forms r occasionally found in mainland Scotland and elsewhere , indicating some gene flow from faroensis or zetlandicus , subspecies formerly considered to be isolated .