THE BIRDS OF ALGERIA. 3 



effectually isolated from the remainder of Africa as 

 if the sea itself divided them. Indeed, the barrier 

 of desert sand that surrounds them on the south 

 and east has proved even more effectual in barring 

 the spread of bird-life northwards, so that their avi- 

 fauna shows much more affinity with Europe than 

 with the Ethio[Han region. North Africa from 

 Morocco to Barbary is as completely an island as 

 if the Mediterranean surrounded it, and in many 

 respects its resident avifauna is of a strictly insular 

 character. We find numbers of European or 

 Atlantic island species represented by peculiar 

 forms, and tliese again in many cases are replaced 

 by desert races, as we proceed southwards into the 

 Sahara, The variety in the physical aspect of this 

 region is very great, consequently the avifauna is 

 of an equally diversified character. The great chaiu 

 of the Atlas, whose highest peaks are upwards of 

 7,500 feet above sea-level, retaining a snowy mantle 

 until June, runs from east to west throughout the 

 northern portion of the entire region, and has a 

 considerable influence on its avifauna, climaticallv 

 and otliervvise. The region is divided into three 

 very distinct areas, each of which is characterizetl 

 by a more or less specialized fauna. From the 

 coast southwards to the Atlas we have the region of 



