The bird order Passeriformes is not only the most recent order of birds to appear, it is also the one which possesses the greatest number of modern families and species.  More than half the species of modern birds belong to this order.  They can be found in virtually the entire world (except Antarctica and a few islands).  This group is often referred to as the “perching birds” because of modifications of the foot (such as toes on the same level and a large rearward facing toe) which are adaptations for perching.  None are truly aquatic.  Most passerine birds are small, with the largest members being crow-sized.  One of the modifications which is most evident in this group is a syrinx which is especially adapted for song production. 

     In the Order Passeriformes, there are two suborders, Tyranni (suboscines) and Passeri (the oscines).  The syrinx of suboscines is generally not as specialized for song production as that of oscines.  Virtually all suboscines occur in North and South America and the greatest number live in the tropics.