THE ARTISTS BIRDS. 193 



are summer visitors to our islands, and all are 

 remarkable for their gregarious habits and dexterity 

 of aerial movement. These four species possess 

 the following characteristics in common. They 

 have a black cap, extending on to the nape, and 

 the colour of the upper parts is French gray, 

 darkest on the quills and wing coverts. The wings 

 are long and pointed, the tail is acutely forked, the 

 outermost feathers being remarkably long and 

 narrow, whilst the beak is long and slender and 

 nearly straight from the base to the tip. The 

 largest and rarest of these species, the Sandwich 

 Tern (Sterna cantiaca), is characterized by its size, 

 its black beak tipped with yellow, proportionately 

 less acutely forked tail, and pure white under 

 surface. The Common Tern (Sterna hirundo) and 

 the Arctic Tern (Sterna arctica] are very similar in 

 appearance, but peculiarities of the former species 

 are its orange-red beak tipped with black, and very 

 pale French gray (almost white) underparts, the 

 beak of the latter species being rich crimson, and 

 the underparts a much darker tint of gray. The 

 Lesser Tern (Sterna minuta) is the smallest Euro- 

 pean species, and is further distinguished by its 

 white forehead, yellow beak tipped with black, and 

 white underparts. We need only make a passing 



