PANAMIC-PACIFIC PELECYPODA J7 



zone is due entirely to presence of the Peruvian Current. A cessation of the 

 flow of this stream or of the submarine upwellings which accompany it, 

 would permit the southward invasion of much warmer waters from the 

 west or the open Pacific and from the north. The Peruvian fauna would 

 be forced to retreat southward and the more aggressive, Panamic-Pacific 

 species would move in to take its place. This faunal shift, back and forth, 

 has occurred repeatedly. 



THE PAITA BUFFER ZONE WITH A LIST OF ITS PRINCIPAL SPECIES 

 As seen from the previous discussion, the northern or Panamic-Pacific 

 and the southern or Peruvian faunas meet and to a certain extent inter- 

 mingle along the coast of northwestern Peru between Cabo Blanco at the 

 south end of the Gulf of Guayaquil and Punta Aguja at the western tip of 

 the Bay of Sechura. This is an overlap region of about two degrees of lati- 

 tudinal spread or about 120 nautical miles. The marine species of this 

 overlap region belong properly neither to the Panamic or the Peruvian 

 faunal provinces, hence the name of the "Paita Buffer Zone" is here pro- 

 posed, its name taken from the city or bay of Paita located in its central 

 portion. Both on land and in the sea, this is truly a transitional region. 

 At Tumbez, and throughout most of southwestern Ecuador, the country is 

 covered with a good growth of small trees, bushes, and cacti. Along the 

 banks of the many esteros or inlets, there are stands of tall mangrove, a 

 flora maintained by a fairly heavy and regular rainfall during the summer 

 months. Further south in Peru, this zone of semiarid vegetation retreats 

 deeper inland, following the base of the Amotape Mountains or retained 

 only on some of the higher hills. In the vicinity of the coast, the climate, 

 tempered by the winds blowing in from a colder sea, are dry and dessicating, 

 the rainfall sparse and irregular in normal years. Beyond Cabo Blanco, 

 desert conditions set in rapidly and plant growth becomes less plentiful or 

 confined largely to river and quebrada bottoms where some moisture re- 

 mains in the subsoil. At Paita, Sechura, and points further south, desert 

 conditions become more strongly intensified. 



Interesting accounts of the bird life along this transitional zone in 

 northwestern Peru have been given by R. C. Murphy in several papers 

 and books. Some of the northern or tropical sea birds which find their 

 southern limits of range in the Paita Buffer Zone are: The West Indian 

 ?e\ican( Pelecanus occidentalis), the Caribbean Man-O-War bird (Fregata), 

 the Roseate Spoonbill, and several others. The common gannet in the 

 Paita Buffer Zone is the Blue-Footed Booby (Sida nebouxii) but which 

 ranges somewhat further south, nesting in large numbers on the islands of 

 Lobos de Tierra. Regular visitors in the Paita Buffer Zone from the south, 

 especially in the early months of the year, are the large Peruvian pelican 

 (Pelecanus thagus), a strictly marine species, the Piquero (Sula variegata), 

 the White-breasted Cormorant or Guanay (Phalacrorax bougainviUei) , and 

 the Kelp Gull (Larus dominie anus) . The Peruvian Penguin {Spheniscus 

 humboldti) is rare in the Paita Buffer Zone but has been observed in the 

 Bay of Sechura. The sea lion (Otaria juhata) was formerly common at 



