Of the islands of coral origin, the atolls have been studied in some detail at the beginning of the century, especially in the Maldives (bibliography in Stoddart and a t Cocos-Keeling, on which Darwin worked and which has been studied more recently by Gibson-Hill (bibliography in Sachet and Fosberg 1955).Most of the similar high limestone islands in the Pacific have been destroyed for guano (Ocean Island, Nauru, and Makatea being the worst examples), and those that remain (such as Henderson and Vostok) a r e s o f a r from continental land a s to be biologically impoverished.
PREVIOUS INVESTIGATIONS
Second, it is oceanic, in the sense that there is no evidence of any previous terrestrial connections with continental areas, so the living organisms must have arisen by normal processes of dispersal; but at the same time the relative proximity of Africa, especially Madagascar and the Comoros, means that the likelihood of successful colonization from these sources was high. Due to the devastation of nearby islands that originally had very similar ecosystems, Aldabra is of such special importance in the raised coral atoll category.
PRESENT INVESTIGATIONS
This bulletin was designed to summarize the knowledge of Aldabra as part of the work done during the 1966 expedition by Gaymer during his two visits as a member of the Bristol Seychelles expedition on the natural history of birds, again with reference to land birds. .
ACKNOWLEDGMENTS
Finally, in January to March 1968, the third part of the expedition, a wet season group will concentrate on terrestrial flora and vegetation and terrestrial zoology. Mr Daniel Labworth very kindly gave permission to quote parts of the commercial lease for Aldahra, signed in 1955, used in Chapter 2.
Chapter 2
LOCATION AND REGIONAL SETTING
Little do I know of the c r u s t a l s t r u c t u r e north of the Comoros, or between Aldabra and Farquhar and Madagascar and the Amirantes. Aldabra lies northwest of the Indian Ocean belt of tropical cyclones, but it is occasionally affected.
GEOMORPHOLOGY AND GEOLOGY
Coastal Morphology (a) Seaward side
The upper part of the rock ramp is deeply and intricately dissected by holes in the salt spray solution. Much of the lagoon floor is covered by a thin layer of calcium carbonate mud overlying a n i r e g u l a r rock floor.
Surface Morphology (a) Geneva1 featuves
Aerial photographs indicate a watershed between the Main Channel and the East Channel, as evidenced by bottom sediment patterns, 4-5 miles west of the latter. The bottoms of the holes are round on top and flat, and at lower levels contain salt water.
Origin of Aldabra Landforms
The nature of the platinum s u r f a c e is highly variable, with facies changes in the back-reef deposits. In the case of platinum, we need to know the relationship between i t s near-equilibrium surface and tidal levels.
FLORA AND VEGETATION
The central part of the island is formed by a relatively undissected ridge that rises to more than 30 feet. Of the 68 species, Hemsely considered 18 to be endemic to Aldabra itself (forming about 10 percent of the total flora), and 13 to be restricted to the Aldabra group (Assumption, Cosmoledo, Astove, St P i e r r e, Gloriosa).
Mixed Scrub
Pemphis Thicket
In these transition zones, Pemphis is most dense around the edges of large sinkholes, where it can be almost impassable except by emergency work. The flatness of the ground is coupled with a uniform height (10-15 ft) of vegetation, which makes travel, except by compass, very difficult; and Wharton vividly describes the difficulty of traversing the I'emphis-covered champignons, when he states that "the walking of Aldabra is the most laborious and slow part of movement that I ever undertook: and nothing less than patience, persistence, and a general disregard of time the turtle tribe can make a pleasant abode.
Mangrove Communities
Psammophilous Communities
Man-induced Vegetation
The most common decorative flowering plant, planted around most of the houses in the settlement. T o r t o i s e s and goats crop the lower vegetation, including g r a s s e s , mills and the lower leaves of trees and shrubs, especially in the more open Mixed Scrub.
TERRESTRIAL FAUNA
The common weed Stachytarpheta indica is only found in the West Island settlement and near abandoned fisheries, but on the west side of the East Channel. Birds must have a significant direct effect on leaves and branches and an indirect effect on soil and phosphorus cycling, particularly in large Middle Island breeding colonies, and this also needs further study.
Mammals
Birds
Ti Aldabra ket addaan pay kadagiti naisangayan a porma ti Kestrel Falco newtoni aldabranus, ti Comoro nga Asul a Kalapati nga Alectroenas sganzini minor, ti Madagascar Coucal Centropus e u insularis, ti Madagascar Bulbul Hypsipetes madagascariensis rostratus, ken ti. Ti kababalin ti pannangan dagiti tumatayab iti igid ti baybay kadagiti patad ti lagoon ken ti panagpannurayda kadagiti di naadal nga awan durina nga ayup ket mangsubad iti detalyado nga imbestigasion.
Land Reptiles
Second, environmental disruption, especially through vegetation clearing and the spread of agriculture, such as in the Galapagos, forced the tortoises into more marginal environments, especially on the high islands. Many of the pools, when nearly dry, are green with organic matter, and this results in the formation of concentric drying patches of green or blue around the edges of the pools and on the necks of the turtles.
Insects
Other groups
MARINE BIOTA 1. Turtles
By the end of the l st century (Spurs 1892) the numbers of t u rt l e rapidly declined, and Hornell for the ultimate extinction of exploration continued under the l e s e system without any attempt at conservation.
Other groups
The administrator of the Seychelles opined that "the government is fortunate in having s e c u r e d M r Spurs for a tenant; as it will be gathered from his report. One of the Western channels, P a s s e s , however, may go to one of the Lanier be called.leading Seychelles guano companies.
Introduced Animals and Plants
D'Emmerez de Charmoy became tenant, with James Spurs as manager; and his administration became notorious for the wasteful and inefficient exploitation of the turtle industry (Hornell 1927). It is therefore remarkable that the effects of introduced species on Aldabra have so far been so limited; although the possible effects of the s p r e a d of the large p r e d a t o r s and competitors already present in the South Island to other parts of the atoll must not be ignored.
Exploitation and Conservation
That the l e s e e shall be the guardian and protector of all wild life and all the r e s o u r c e s of the Islands and of the surrounding seas. All the conservation measures discussed so far remain in force, despite the change in the status of Aldabra.
A NOTE ON PLACE NAMES
With the British Territory Order in Council in 1965, Aldabra was separated from the Seychelles colony to form a new Territory together with Farquhar, Desroches and the islands of the Chagos archipelago.
Main islands Polymnie
These names were created before the existence of the settlement, so there is no case for using the name Island of the settlement.
Channels
Land names
- ASSUMPTION g046's., 46O31'E
- ASTOVE 10°06'S., 47O45'E
- GLORIOSA 11°34's., 45O13'E
- COSMOLEDO 9°41'S., 47'35'E
- ST PIERRE 9°19'~., 50'43'~
- PROVIDENCE g014'S., 5 1 ° 0 2 ' ~
- Chapter 4
For the information on insects I have relied on the summary by Scott (1936) r e - rather and no special s e a r c h has been made of the papers in the Percy Sladen Expedition Reports. The dunes are covered with Suriana on the windward side, and with Scaevola and Tournefortia up to the sky. A deciduous s c r u b covers the s u r f a c e on the wider parts of the eastern side, with regular Pisonia trees.
Stachytarpheta indica is the most common of the herbs that live on soil residues.
- HISTORICAL INTRODUCTION
- ACKNOWLEDGMENTS
- SYSTEMATIC LIST
- ASSUMPTION g046's., 46031fE
- ASTOVE 10°06'S., 47'45'E
- GLORIOSA 11°34's., 45'13'E
- COSMOLEDO g041'S., 47'35'E
- ST PIERRE g019'S., 50'43'~
Goodwin for examining material from the turtledove Streptopelia picturata with me at the British Museum. For the information on insects I have relied on Scott's summary (1936) and no special research has been done on the papers in the Percy Sladen Expedition Reports. A deciduous thicket covers the surface of the wider parts of the eastern side, with Pisonia trees frequent.
The center of the island is close to sea level and has a small tidal pool.
SYSTEMATIC LIST
According to Gaymer (1966), about fifty flamingos live in the southeast of the atoll and probably breed there. In the British Museum is another such (unsexed) specimen collected at Aldabra in October 1906, part of the bequest of Howard Saunders. In view of the above, it is remarkable that due to the visit of H.M.S.
Collected by Abbott at Aldabra and breeding by thousands on small i s l e t s in the lagoon (Ridgway 1895, 527).
TRENDS O F VARIATION Status
Due to lack of development, Aldabra has none of the following four introduced species that occur on Grand Comoro and quite common in the Comoros as a whole: Numida meleagris, Agapornis cana, Acridotheres. Aldabra also has none of the 10 African-derived species found on Grand Comoro, and mostly generally on the Comoros, no doubt because it is more distant from Africa. Of the f i r s t four species listed from Aldabra in Table 9, only Butorides striatus is on the Grand Comoro list.
Report of a research visit to St. P i e r e, Astove, Cosmoledo, Assumption and the Aldabra Group of the Seychelles.
Chapter 5
- G E N E R A L OBSERVATIONS
- Mixed Scrub on Platin
- Pemphis Thicket on Champignon
- The Settlement
Probably the most common are Sun, Fody, Bulbul and White Eye. Most land birds are common here, with the exception of the Pied Crow and the White-throated Rail, the latter of which is restricted to mangroves, Pemphis s c r u b and the beaches of Middle Island and Polymnie. Where mixed forest is close, the Sunbird and the White-eye are sometimes seen and at least the f o r m e r may nest.
Both species also take advantage of the many Casuarina trees along the beach, and Fody breeds in the lower branches.
In the Comoros, Benson (1960) collected a female of this species containing an almost fully developed egg on November 2nd, while in Madagascar Rand (1936) noted that A. madagascariensis breeds from July to March. In the Comoros, Benson (1960) had evidence of this species breeding from August to November, while in Madagascar Rand (1936) found that the season probably extended from at least July to October. The breeding season probably lasts from November to January, although in the Comoros Benson (1960) gives evidence that breeding begins as early as September, and in Madagascar Rand (1936) gives a season that lasts at least from September to January.
Males sing loudly in the breeding season, which is prolonged, lasting at least from September to January (Abbott in Ridgway 1895).
- Breeding Species
- ACKNOWLEDGEMENTS
- REFERENCES
- Chapter 6
Flocks of up to several hundred feed on exposed sand and mud over the west reef and in the lagoon. The following species occur in large numbers in the creeks and pools of the mangroves around Bras Takamaka and elsewhere, and sometimes around the outer coast and in the lagoon at low tide: Turnstone Arenaria interpres, Whimbre l Numenius phaeopus, Sanderling Crocethia alba. I would also like to express my appreciation for the invaluable Preliminary Field Guide to the Birds of the Indian Ocean by Watson, Z u s i and Storer (1963).
Abbott in the Seychelles, Amirantes, Gloriosa, Assumption, Aldabra, and adjacent islands, with notes on habits, etc., by the collector.
The land birds of the Seychelles and the Aldabras, with a note on the giant tortoise of Aldabra Atoll. A revision of recent colonial Astraeidae that have a variety of corallites (based on material from the Indo-Pacific Ocean and the collections of Paris, Berlin, Vienna, Copenhagen, London and Glasgow). A bibliography of published works relating to the natural history of Seychelles and the neighboring archipelagos.
