The Blue Tit , Cyanistes caeruleus , is a passerine songbird in the family Paridae . It is 10.5 to 12 cm ( 4.2 to 4.8 inches ) long . The Blue Tit , Cyanistes caeruleus , is a 10.5 to 12 cm ( 4.2 to 4.8 inches , ) long passerine bird in the tit family Paridae .