400 PERCY SLADEN TRUST EXPEDITION 



The ocean currents in the neighbourhood are both uniform in direction and strong 

 (2 — 4 knots) ; they run from east to west, varying slightly to the north or south according 

 to the seasons, which are respectively those of the S.E. Trades and of the N.W. Monsoon 

 or calm season. The S.E. Trade winds blow strongly from May to October, and the 

 season is one of drought, during which the vegetation on the islands becomes parched, 

 trees lose their leaves, and life generally seems at a standstill. Owing to the partial 

 coincidence of wind and ocean current, the latter is at its strongest during this season. 

 In November the S.E. Trades break and the calm season sets in, for, though sometimes 

 called the season of N.W. Monsoons, the latter winds rarely extend to such southern lati- 

 tudes. The rainfall is very heavy, and, as a rule, a dead calm prevails, though at times 

 heavy squalls may spring up from any point of the compass, and very occasionally a 

 cyclone is experienced. The temperature is higher than that of the S.E. Trades, and often 

 stands for long periods at or over 100° F., while the atmosphere is almost saturated. The 

 calm season is the one of activity on the islands both for animals and plants. My visit 

 lasted from August 1908 to February 1909, and both seasons were experienced. 



With this introduction I now turn to Aldabra, taking this, the most important, 

 island first. 



II. ALDABEA. (Plates 22—27.) 

 A. Physical Features. (Plate 22.) 



Aldabra is situated in latitude 9° 22' 35" South and in longitude 46° 14' 41" East, 

 and thus lies 240 miles from Cape Amber and 600 miles from the Seychelles, while the 

 African coast is distant only some 400 miles. In form the island is an atoll measuring 

 25 miles long and from 4 to 10 miles wide, the long axis running approximately east 

 and west. In total area the atoll perhaps measures 120 square miles, of which some 60 

 are land, though, owing to the presence of numerous islands in the lagoon and of a 

 large area of mangrove swamp, half land half water, this estimate cannot be considered 

 accurate. 



The land consists of the land-rim, forming the circumference of the atoll, and of the 

 various small islands in the lagoon. The former is unusually perfect, and is divided by 

 narrow passes into four main islands, named respectively Picard, Polymnie, Malabar, and 

 Main or South Island. Picard is a small island situated in the north-west, measuring 

 about 2 square miles, and is divided from Polymnie by the Grande Passe, 750 yards wide, 

 of which about 400 yards are deep channel. Polymnie. another small island about 1 square 

 mile in area, may really be considered part of the larger Malabar Island, from which 

 it is divided by a shallow pass, the Johnny Channel. Malabar itself is some 9 miles long, 

 and averages £ mile in width ; it is divided from Main Island by Passe Houareau, a 

 large pass 400 yards wide, though the actual channel is narrower. Main island varies 

 greatly in width, in the east measuring as much as 5 miles, while at one place in the south 

 it is only ^ mile from the lagoon to the sea : it forms at least two-thirds of the total 

 circumference of the land rim, extending from the north-east round the south of the atoll 

 to the west near Picard Island, from which it is divided by the western channels, a series 



