D. R. S t o d d a r t , C . W. Benson, and J . F. Peake
I n t r o d u c t i o n
Because o f t h e i r rugged t e r r a i n and l a c k o f s u r f a c e w a t e r , e l e v a t e d r e e f - l i m e s t o n e i s l a n d s a r e o f t e n u n s u i t a b l e f o r human s e t t l e m e n t . A s a r e s u l t o f g r e a t e r environmental d i v e r s i t y and p o s s i b l e g r e a t e r age t h a n t h e sand cays o f s e a - l e v e l c o r a l a t o l l s , such i s l a n d s f r e q u e n t l y p o s s e s s l a r g e r and more d i v e r s e faunas and f l o r a s . Yet because many p o s s e s s l a r g e r e s o u r c e s o f phosphate d e r i v e d from b i r d guano, t h e y have o f t e n been s u b j e c t e d t o a d e g r e e of human i n t e r f e r e n c e uncommon on i s o l a t e d i s l a n d s b e f o r e t h e development o f a i r f i e l d s and s i m i l a r i n s t a l l a t i o n s . Examples o f e l e v a t e d r e e f i s l a n d s where such major m o d i f i c a t i o n h a s t a k e n p l a c e i n c l u d e Makatea i n t h e e a s t P a c i f i c , Nauru, Niue and Ocean i n t h e c e n t r a l P a c i f i c , and Christmas i n t h e e a s t e r n I n d i a n Ocean.
The r e s u l t s of massive mining d i s t u r b a n c e on i s l a n d ecology a r e o f i n t e r e s t , s i n c e t h e y may p r o v i d e a g u i d e t o t h e r e s u l t s o f o t h e r k i n d s of major h a b i t a t d i s t u r b a n c e , i n c l u d i n g t h e c o n s t r u c t i o n o f a i r f i e l d s and m i l i t a r y b a s e s . Such c o n s t r u c t i o n work i n v o l v e s t h e c l e a r i n g o f n a t i v e v e g e t a t i o n and d e s t r u c t i o n o f h a b i t a t s , and a l s o t h e p r e p a r a t i o n of new h a b i t a t s f o r c o l o n i s a t i o n by i n t r o d u c e d p l a n t s and a n i m a l s . We know l i t t l e o f t h e long-term r e s i l i e n c e of i n d i g e n o u s b i o t a s on i s l a n d s , i n c l u d i n g t h o s e s u b j e c t t o such major i n t e r f e r e n c e , except t h a t changes i n v o l v i n g e x t i n c t i o n a r e i r r e v e r s i b l e ( S t o d d a r t 1968a, 1968b, MacArthur and Wilson 1967, Mayr 1 9 6 5 ) .
Assumption I s l a n d , 27 km s o u t h e a s t of Aldabra, p r o v i d e s an example o f t h e e c o l o g i c a l e f f e c t s of s u r f a c e p h o s p h a t e mining over t h e l a s t s i x t y y e a r s (Baker 1963). With a f a u n a and f l o r a s i m i l a r t o t h o s e o f Aldabra, though s m a l l e r , b e f o r e mining began, i t p r o v i d e s d a t a on t h e c a p a c i t y o f p l a n t s and animals t o s u r v i v e v e g e t a t i o n c l e a r a n c e and human s e t t l e m e n t , and on t h e i n v a s i o n s and c o l o n i s a t i o n s which have taken p l a c e s i n c e s e t t l e m e n t began. Assumption was v i s i t e d by a p a r t y from t h e Royal S o c i e t y E x p e d i t i o n t o Aldabra on 15-16 September 1967, and t h i s p a p e r r e c o r d s t h e o b s e r v a t i o n s made and compares them w i t h p r e v i o u s a c c o u n t s , mostly from pre-mining t i m e s . F a m i l i a r i t y w i t h t h e fauna and f l o r a o f Aldabra meant t h a t maximum advantage c o u l d b e t a k e n o f t h i s s h o r t v i s i t .
Apart from h y d r o g r a p h i c s u r v e y s i n 1823 and 1878, Assumption was f i r s t v i s i t e d by W . L. Abbott, who c o l l e c t e d b i r d s , p l a n t s and i n s e c t s
A t o l l Research B u l l e t i n No. 136: pp. 121
-
145, 1970I
. . . W i n d w a r d p e r c h e d sand b e a c h C h o m p i g n o nI
0 m i l e
I
L..d____]I
F i g . 6. Assumption
i n September 1892. The o r n i t h o l o g i s t M. J . N i c o l l s p e n t 12-13 March t h e r e , and was followed by R. Dupont ( b i r d s , i n s e c t s , p l a n t s ) , 19-21 September 1906, and by J. C . F. F r y e r (geology, g e n e r a l o b s e r v a t i o n s , i n s e c t s ) , 6-13 September 1908. The i s l a n d was u n i n h a b i t e d u n t i l J u n e 1908, when a guano-mining s e t t l e m e n t was e s t a b l i s h e d on t h e n o r t h w e s t c o a s t : t h e o b s e r v a t i o n s o f t h e s e e a r l i e r workers t h u s r e c o r d e d t h e p r e - mining s t a t e o f t h e i s l a n d b i o t a . Table 12 l i s t s t h e s e and l a t e r
Table 1 2 . S c i e n t i f i c S t u d i e s a t Assumption I s l a n d Date
-
Study-
Reference1756 Aug. 15 Nicholas de Morphey, g e n e r a l Horsburgh (1809) 1823 Richard Owen, h y d r o g r a p h i c s u r v e y Adm.Ch.718(1878) 1878 W . J . L . Wharton, h y d r o g r a p h i c Adm.Ch.718(1879)
s u r v e y
1892 S e p t . W . L. Abbott, b i r d s Abbott (1893),
Ridgway (1895) 1901 Oct. 13 H . A ' C . Bergne, g e n e r a l Bergne (1901)
1906 March 12-13 M. J. N i c o l l , b i r d s N i c o l l (1906, 1908) 1906 S e p t . 19-21 R . Dupont, b i r d s , i n s e c t s , p l a n t s Dupont (1907)
1908 S e p t . 6-13 J . C . F. F r y e r , geology, i n s e c t s Fryer (1911) 1910 R . Dupont, i n s e c t s , p l a n t s
1916 R . Dupont, p l a n t s Hemsley (1919)
1937 L. D . E . F. Vesey-FitzGerald Vesey-FitzGerald
v e g e t a t i o n , b i r d s (1941, 1942)
1956 H. Legrand, L e p i d o p t e r a Legrand (1965)
1956 W . T r a v i s , underwater o b s e r v a t i o n s T r a v i s (1959) 1959 H. Legrand, M. Gerber, L e p i d o p t e r a Legrand (1965) 1960 Oct. 13-16 B. H. Baker (geology) and C . J . Baker (1963),
P i g g o t t ( s o i l s ) P i g g o t t (1961, 1968)
1964 H.M.S. Owen, Cdr D .
-
W . Haslam: Bourne (1966)s u r v e y , b i r d s
1964 R. E . Honegger, b i r d s , r e p t i l e s Honegger (1966) 1964 Nov. 10 B r i s t o l S e y c h e l l e s E x p e d i t i o n : T h i s r e p o r t
M. J. Penny, M. Penny, R . Gaymer and o t h e r s , b i r d s
1965 Oct. 3 R. G a p e r , b i r d s This r e p o r t
1967 March J . F. G . L i o n n e t , H. A . Beamish, i n s e c t s ; H. A. H i r t h , t u r t l e s
1967 S e p t . 15-16 Royal S o c i e t y p a r t y : D . R . S t o d d a r t T h i s r e p o r t (geomorphology, p l a n t s ) , C . W.
Benson ( b i r d s ) , J . F. Peake ( l a n d i n v e r t e b r a t e s ) , J . H. P r i c e (marine a l g a e ) , J. M. Boyd, E . N . Wright
( b i r d s )
1967 Oct. 8 M. D . Gwynne, D. Wood, I . S . C . Fosberg and Renvoize P a r k e r , p l a n t s and b i r d s (1970), P a r k e r (1970) 1968 J u l y 31 Royal S o c i e t y p a r t y : J. F r a z i e r
R. Hughes, J . Gamble, R. Lowery
s c i e n t i f i c i n v e s t i g a t i o n s . The Royal S o c i e t y p a r t y i n September 1967 c o n s i s t e d of D. R . S t o d d a r t (geomorphology, p l a n t s ) , C . W . Benson ( b i r d s ) , J . F . Peake (land i n v e r t e b r a t e s ) , J . H. P r i c e (marine a l g a e ) , J . Morton Boyd, and E . N. Wright ( b i r d s ) . A f u r t h e r Royal S o c i e t y p a r t y , comprising R . Lowery, J . Gamble, 3 . F r a z i e r and R. Hughes, made a b r i e f v i s i t on 31 J u l y 1968.
Topography
Assunlption ( F i g u r e 6) i s a r a i s e d r e e f - l i m e s t o n e i s l a n d , probably s i m i l a r i n o r i g i n t o Aldabra b u t without a c e n t r a l lagoon. I t i s 6 km long, n o r t h e a s t t o s o u t h w e s t , and 0 . 6 t o 1 . 6 km wide, w i t h an a r e a o f 1 0 . 5 sq km (compare t h e l a n d a r e a o f Aldabra, 155 s q km). The l i m e s t o n e r i s e s t o a maximum h e i g h t of about 6 m above s e a - l e v e l , and forms c l i f f s a l o n g t h e n o r t h e r n h a l f o f t h e e a s t c o a s t . As on t h e s o u t h c o a s t o f Aldabra, t h e c l i f f s a r e topped by a perched beach up t o 1 . 8 m t h i c k and 18 m wide, which a t t h e head of s m a l l coves d e v e l o p s i n t o low dunes
3 - 4 . 5 m t h i c k . The perched beach approaches c l o s e t o t h e c l i f f - t o p a l o n g t h e c e n t r a l p a r t o f t h e c o a s t , b u t moves i n l a n d towards t h e n o r t h , r e - v e a l i n g a c l i f f - t o p p l a t f o r m o f p i n n a c l e d l i m e s t o n e . The c l i f f s a r e u n d e r c u t o n l y i n coves, and when f a c i n g seaward a r e more ramp-like; t h e y overlook a r o c k - c u t a b r a s i o n p l a t f o r m 90-200 m wide ( P l a t e s 20 and 2 1 ) . T h i s p l a t f o r m l a c k s growing c o r a l s , and towards i t s o u t e r edge h a s i n p l a c e s mushroom r e s i d u a l s of a s u r f a c e a t l e a s t 0.6 m h i g h e r ( P l a t e 2 2 ) . S e v e r a l high dunes, t h e i r s t e e p e r s l o p e f a c i n g i n l a n d , a r e found a l o n g t h e s o u t h e a s t c o a s t ; t h e i r h e i g h t s range from 14-28 m above s e a - l e v e l . The s m a l l e r h i g h dunes have a s i m p l e o u t l i n e , b u t t h e l a r g e r ones a r e c u t by v a l l e y s on t h e i r seaward s i d e and may be e r o d i n g . Most o f t h e west c o a s t c o n s i s t s o f a narrow s a n d - f l a t with low dunes, banked a g a i n s t a p r e v i o u s l y eroded c l i f f - l i n e . The c o a s t below b o t h t h e h i g h dunes and t h e w e s t e r n s a n d - f l a t i s formed by a wide sand beach.
The main body o f t h e i s l a n d c o n s i s t s o f a d e e p l y - p i t t e d and eroded champignon, with t i d a l s o l u t i o n h o l e s up t o 6 m deep and g e n e r a l l y s t e e p - s i d e d . Round t h e margins of t h e i s l a n d t h e r e i s a h i g h e r r i m w i t h a l e s s d i s s e c t e d and much smoother s u r f a c e s t a n d i n g 1 . 2 - 1 . 8 m above t h e
champignon. T h i s s u r f a c e may b e compared t o t h e pav; o f Astove, and t o t h e s u r f a c e o f t h e Aldabra 8 m r i d g e , where u n d i s s e c t e d , r a t h e r t h a n t o t y p i c a l Aldabra p l a t i n . Baker (1963, 101) s u g g e s t s t h a t t h e s l a b b y lime- s t o n e a s s o c i a t e d w i t h t h i s smoother s u r f a c e i s formed from l i t h i f i e d c a r b o n a t e s a n d s . Phosphates have accumulated b o t h on t h e s u r f a c e , where l a r g e q u a n t i t i e s have now been s c r a p e d away, and i n t h e s o l u t i o n h o l e s , many o f which a r e l a r g e r below ground t h a n a t t h e s u r f a c e . More
i n f o r m a t i o n on mining a c t i v i t i e s would be needed b e f o r e a t t e m p t i n g an e x p l a n a t i o n o f t h e p r e s e n t s u r f a c e topography on Assumption.
P i g g o t t (1961, 1968) d i v i d e s t h e s o i l s o f Assumption i n t o t h r e e t y p e s : p h o s p h a t i c Desnoeufs S e r i e s on t h e l i m e s t o n e s , now l a r g e l y dug f o r
phosphate; Farquhar S e r i e s on t h e dunes; and v a r i a b l e Shioya S e r i e s e s p e c i a l l y on t h e leeward sand f l a t .
Climate
R a i n f a l l r e c o r d s have been maintained a t t h e S e t t l e m e n t s i n c e November 1964. The t o t a l f a l l f o r 1965 was 813 mm, f o r 1966 920.5 mm, and f o r 1967 ( t o 16 September only) 724.1 mm (Table 1 3 ) . R a i n f a l l i s c o n c e n t r a t e d from December t o March, b u t i s r a t h e r v a r i a b l e from y e a r t o y e a r . September and October a r e almost r a i n l e s s . S e v e r a l heavy f a l l s have o c c u r r e d d u r i n g t h e p e r i o d o f r e c o r d : 51.3 mm on 15 A p r i l 1965,
105.9 mm on 17 J a n u a r y 1966, 102.6 mm on 5 March 1966, 59.2 mm on 29 A p r i l 1966, 113.8 mm on 30 A p r i l 1966, and 8 1 . 3 mm on 14 December 1966.
I n 1966 t h e heavy f a l l s on t h e f o u r days mentioned accounted f o r 42 p e r c e n t of t h e t o t a l annual r a i n f a l l . As a t Aldabra t h e p e r i o d of t h e S o u t h e a s t Trades (June-November) i s t h e d r y s e a s o n , t h a t of t h e n o r t h - w e s t e r l i e s and calms (December-May) t h e wet s e a s o n . No t e m p e r a t u r e r e c o r d s have been k e p t .
V e g e t a t i o n
The v e g e t a t i o n o f Assumption can be d e s c r i b e d , b a s e d on b r i e f r e c o n n a i s s a n c e o n l y , i n terms o f e i g h t communities:
1. perched beach community 2 . h i g h dune community
3 . Pemphis community o f t h e c l i f f s 4 . west c o a s t sand beach community
5 . mixed s c r u b community o f t h e champignon
6 . h e r b s and g r a s s e s community of t h e pave' o r p l a t i n 7. s o l u t i o n - h o l e community
8 . s e t t l e m e n t v e g e t a t i o n Perched beach community ( P l a t e 23)
The narrow zone o f sand perched on t o p o f t h e seaward c l i f f s a l o n g t h e e a s t c o a s t c l o s e l y r e s e m b l e s t h a t on t h e s o u t h c o a s t o f Aldabra, except t h a t t h e c l i f f - l i n e i s more i r r e g u l a r . The beach i s s u b j e c t t o c o n s t a n t s p r a y d u r i n g t h e Trades and t o wave-swash a t e x c e p t i o n a l t i d e s . A s a r e s u l t a r e a s on t h e seaward s i d e o f t h e perched beach l a c k
v e g e t a t i o n c o v e r . The v e g e t a t i o n c o n s i s t s o f a mosaic o f d i s c r e t e a r e a s o f Sporobolus v i r g i n i c u s and S c l e r o d a c t y l o n macrostachyum, bounded
s h a r p l y i n l a n d by a t r a n s i t i o n t o t h e r o c k - s u r f a c e c o v e r o f Sarcostemma v i m i n a l e and Plumbago a p h y l l a . The dominant Sporobolus turf-
d e n s e r and l o n e e r (uu t o 230
- .
A mml than a t Aldabra. where it i s c l o s e - cropped by t o r t o i s e s . Few o t h e r p l a n t s a r e p r e s e n t : s m a l l p a t c h e s of Stenotaphrum clavigerum, inconspicuous i n d i v i d u a l s o f Launaea sarmentosa and S i d a p a r v i f o l i a , and i n f r e q u e n t s h r u b s o n l y where s m a l l dunes have developedT a b l e 1 3 . Monthly r a i n f a l l a t ~ s s u m ~ t i o n '
Jan Feb Mar APT May J u n e J u l y Aug Sep Oct Nov Dec T o t a l
1964 2 6 . 6 7 47.75
1965 1 5 1 . 6 4 44.96 9 2 . 7 1 1 7 0 . 9 4 4 6 . 4 8 6 0 . 7 1 31.50 47.50 3 . 8 1 6.35 7 0 . 6 1 8 6 . 3 6 813.56 1966 204.72 5 9 . 1 8 1 9 2 . 2 8 1 9 8 . 8 8 3 2 . 7 7 20.07 1 8 . 2 9 9 . 9 1 1 3 . 4 6
-
1 9 . 8 1 1 5 1 . 1 3 920.50 1967 1 3 6 . 4 0 1 8 4 . 9 1 9 3 . 9 8 1 3 6 . 9 1 1 4 . 6 1 1 1 . 9 4 46.74 59.20 1 . 2 7 2S o u r c e : S e t t l e m e n t Manager, Assumption
1. F i g u r e s i n nun c o n v e r t e d from i n c h e s and t e n t h s 2. To 1 6 September o n l y
High dune community ( P l a t e s 24-27)
The h i g h dunes o f t h e s o u t h e a s t c o a s t have a c o m p a r a t i v e l y g e n t l e b u t i r r e g u l a r seaward s l o p e and a s t e e p landward s l o p e . V e g e t a t i o n on t h e seaward s l o p e i s v a r i a b l e , some a r e a s being dominated by g r a s s e s
(Sporobolus . v i r g i n i z u s
- - - - - -
a n d S c l e r o d a c t y l o n macrostachyum), o t h e r s with s h r u b s , but t h e c h a r a c t e r i s ' t i c f ~ a t u r s s of t h i s comn~unitv a r e t h e l a r g e a r e a s b f b a r e and sometimes mobile s a n d . I n t h e a r e a s dominated by-
g r a s s s p e c i e s t h e d e n s i t y o f t h e v e g e t a t i o n i s f r e q u e n t l y s o low t h a t l a r g e a r e a s of b a r e sand a r e v i s i b l e . The dominant s h r u b s a r e low wind- trimmed Scaevola t a c c a d a and bushy S u r i a n a m a r i t i m a , w i t h o c c a s i o n a l T o u r n e f o r t i a a r g e n t e a . The ground under t h e s h r u b s , and t h e w a l l s and f l o o r s o f t h e t r a n s v e r s e v a l l e y s , a r e l a r g e l y b a r e , w i t h clumps o f
F i m b r i s t y l i s cymosa and s c a t t e r e d Euphorbia i n d i c a 30-60 cm t a l l . On t h e c r e s t and backslope of t h e dunes, T o u r n e f o r t i a i s t h e dominant s h r u b , w i t h F i m b r i s t y l i s and p a t c h e s o f P o r t u l a c a s p . and
-
S i d a p a r v i f o l i a . A t t h e f o o t o f t h e h i g h dunes on t h e seaward s i d e t h e r e i s a narrow sand f l a t with S u r i a n a and T o u r n e f o r t i a , and a ground c o v e r o f Ipomoeap e s - c a p r a e e x t e n d i n g o n t o t h e beach. I n t h e s h e l t e r e d a r e a immediately
-
landward of t h e high dunes t h e r e i s a f l e s h y mat o f P o r t u l a c a o l e r a c e a and a narrow b e l t of s t u n t e d T h e s p e s i a populneoides woodland. Some o f t h e shrubs on t h e dunes a r e overgrown with Cassytha f i l i f o r m i s , and on i s o l a t e d lower dunes t o t h e n o r t h T o u r n e f o r t i a and S c a e v o l a bushes a r e s o h e a v i l y overgrown t h a t t h e y a r e almost i n v i s i b l e .C l i f f s
-
C l i f f s l a c k i n g a perched o r s e a - l e v e l sand beach occur a t t h e n o r t h e r n end of t h e i s l a n d , where t h e r e i s a s m a l l clump o f Pemphis
a c i d u l a . Thomasset ( i n Hemsley 1919) n o t e d Pemphis a s "common", b u t -1911, 433) found o n l y "a few t r e e s . . . n e a r t h e west c o a s t . . .(which) do n o t u n i t e t o form bush". Dupont (1907) mapped Pemphis n e a r i t s
p r e s e n t p o s i t i o n . The p r e s e n t d i s t r i b u t i o n i s c l e a r l y a s m a l l r e l i c o f a more e x t e n s i v e c o v e r , though w i t h t h e absence o f s u i t a b l e h a b i t a t probably l e s s e x t e n s i v e t h a n on Aldabra.
West c o a s t sand beach community ( P l a t e s 28 and 29)
This h a s c e r t a i n l y been much a l t e r e d by man, e s p e c i a l l y on t h e s i t e s of t h e p r e s e n t and former s e t t l e m e n t s . Shrubs a r e common a l o n g t h i s sand s t r i p , s p e c i e s i n c l u d i n g S c a e v o l a t a c c a d a , S u r i a n a m a r i t i m a and
T o u r n e f o r t i a a r g e n t e a a l o n g t h e s h o r e , and Clerodendron glabrum 3-5 m t a l l a s h o r t d i s t a n c e i n l a n d . Sophora tomentosa i s o r e s e n t b u t n o t common. I n t h e n o r t h , n e a r t h e o i d s e t t l e m e n t , t h e r e a r e some r a t h e r bushy t r e e s of ~ o r d i a - s u b c o r d a t a , which were i n flower i n September 1967.
The ground cover between t h e s h r u b s l a r g e l y c o n s i s t s of a t h i c k c a r p e t of Cassytha f i l i f o m i s , with Pennisetwn p o l y s t a c h i o n , Amaranthus v i r i d i s and Melanthera b i f l o r a . C a n a v a l i a r o s e a i s an escape from c u l t i v a t i o n n e a r t h e former s e t t l e m e n t . The s a n d - s t r i p v e g e t a t i o n t h u s c o n s i s t s of a
-
m i x t u r e o f n a t i v e and i n t r o d u c e d s p e c i e s .
Mixed s c r u b community
The mixed scrub on t h e e l e v a t e d l i m e s t o n e h a s c l e a r l y been much a l t e r e d by man, and now p r e s e n t s such a d i v e r s e form t h a t any g e n e r a l i - s a t i o n s a r e d i f f i c u l t t o make. Before mining began i t was p r o b a b l y comparable t o t h e more open mixed s c r u b a r e a s of Aldabra. Abbott (1893, 763) n o t e d t h a t t h e s u r f a c e was "not s o d e n s e l y covered w i t h s c r u b a s Aldabra", while N i c o l l (1908, 107) found it " l e s s t h i c k l y covered t h a n G l o r i o s a . The c e n t r a l p a r t i s almost b a r e of v e g e t a t i o n , t h e o n l y growth b e i n g a few low bushes ( h i b i s c u s [ T h e s p e s i a ? ] ) , and a t h i n wiry g r a s s which s p r i n g s from t h e c r a c k s and f i s s u r e s i n t h e c o r a l " . F r y e r (1911,433) s t a t e d t h a t "the v e g e t a t i o n o v e r t h e m a j o r i t y of t h e i s l a n d c o n s i s t s of a t a n g l e d network o f Plumbago (P. a p h y l l a s p . ? ) , Astephanus
(A.
a r e n a r i u s s p . ? ) and numerous low bushes-not i d e n t i f i e d . Small t r e e s such a s Euphorbia A b b o t t i , banyan ( F i c u s s p . ? ) were n o t uncommon, w h i l e Dracaena (D. - r e f l e x a s p . ? ) o c ~ u r r e d ~ ~ a n o - f i l l e d p i t s " .From t h e f l o r i s t i c r e c o r d s of Dupont (1907) and Hemsley (1919), it appears t h a t t h e s c r u b c o n s i s t e d o f T h e s p e s i a p o p u l n e o i d e s , G u e t t a r d a s p e c i o s a , P i s o n i a g r a n d i s , Euphorbia a b b o t t i i , Ficus nautarum, F i c u s P a l d a b r e n s i s and Dracaena r e f l e x a , w i t h a ground cover of C o l u b r i n a a s i a t i c a , Lomatophyllum borbonicum, Solanum a l d a b r e n s e , Capparis c a r t i l a g i n e a , g r a s s e s , sedges and h e r b s . A number of common
c h a r a c t e r i s t i c t r e e s o r s h r u b s o f t h e Aldabra mixed s c r u b have, however, n o t been r e c o r d e d on Assumption, and were n o t s e e n i n 1967: t h e s e
i n c l u d e t h e t r e e s Grewia s a l i c i f o l i a , Ochna c i l i a t a , Vernonia
a l d a b r e n s i s , T e r m i n a l i a b o i v i n i i , and T r i c a l y s i a c u n e i f o l i a , and t h e s h r u b s Mystroxylon aethiopicum, S i d e r o x y l o n inerme, Maytenus
---
s e n e g a l e n s i s , Tarenna s u p r a - a x i l l a r i s , Apodytes d i m i d i a t a and E h r e t i a cymosa. Some may have been p r e s e n t i n former t i m e s b u t were n o t c o l l e c t - ed and a r e perhaps now e x t i n c t on Assumption.
Guano-mining l e d t o l a r g e - s c a l e v e g e t a t i o n c l e a r a n c e . Vesey- F i t z G e r a l d r e p o r t e d i n 1937 t h a t " t h e c e n t r a l a r e a
. . .
has been l a r g e l y c l e a r e d o f v e g e t a t i o n .. . .
A t h i c k secondary mat of Plumbago now c o v e r s t h e whole o f t h i s country" (Vesey-FitzGerald 1942, 1 2 ) . There a r e now v e r y few t r e e s o r t a l l s h r u b s on t h e champignon. In t h e s o u t h t h e r e a r e small t r e e s of Euphorbia a b b o t t i i , and i n h o l e s some bushy F i c u s nautarum, b u t few o t h e r shrubs a r e t a l l e r t h a n 2 m , and t h e n on-wards t h e s o u t h . Between t h e s e t t l e m e n t and t h e high dunes t h e c e n t r a l p a r t of t h e i s l a n d i s dominated by Gossypium hirsutum with a t h i c k ground cover o f Plumbago a p h y l l a and Sarcostemma v i m i n a l e . Shrubs c o l l e c t e d i n t h i s s e c t o r i n c l u d e Clerodenrum glabrum (1.6 m), Acalypha c l a o x y l o i d e s(1-1.3 m), Abutilon f r u t i c o s u m ( m e c a m o n e f r y e r i ( 0 . 6 - 1 m), and Capparis c a r t i l a g i n e a . Ficus a l d a b r e n s i s and G u e t t a r d a s p e c i o s a , n o t e d by Dupont, were n o t seen i n 1967. and t h e l a t t e r mav be e x t i n c t on t h e ~ -~
i s l a n h ; o n l y one almost l e a f l e s s - ~ i s o n i a g r a n d i s w a s s e e n n e a r t h e northwest c o a s t ( P l a t e 3 0 ) .
I n c o n t r a s t t o t h e p o v e r t y o f t h e shrub l a y e r , t h e ground v e g e t a t i o n i s d i v e r s e , but p a t c h y . ^ A p a r t . from Plumbago, Sarcostemma and ~ a s s ~ t l h a ,
- -
~ d t h e i n t r o d u c e d g r a s s Panicum maximum were n o t seen i n 1967, an - - - Capparis and Lomatophyllum a r e uncommon. Close t o t h e s e t t l e m e n t t h e mixed s c r u b i s being invaded by such common weeds a s S t a c h y t a r p h e t a j a m a i c e n s i s and Catharanthus r o s e u s . Dried Nostoc commune was t a k e n from b a r e rock pavement i n t h e c e n t r e o f t h e i s l a n d . I n g e n e r a l t h e v e g e t a t i o n i s s o low o v e r t h e s o u t h e r n p a r t o f Assumption t h a t v i s i b i l i t y i s l i m i t e d more by t h e i r r e g u l a r i t y of t h e ground than by t h e h e i g h t of s h r u b s and t r e e s .
The p a t c h i n e s s o f t h e v e g e t a t i o n needs t o b e s t r e s s e d , a s a r e s u l t o f t h e c o l o n i s a t i o n o f workings of d i f f e r e n t a g e s . There i s a mosaic of p l a n t communities v a r y i n g i n t h e i r s t r u c t u r e , age and s p e c i e s composition;
t h e s e d i f f e r e n c e s can p o s s i b l y b e a s s o c i a t e d w i t h p e r i o d s of human
a c t i v i t y . Shrubs a r e u s u a l l y found on t h e s m a l l a r e a s t h a t have escaped such a c t i v i t y , on i n a r e a s o f o l d e r workings.
~ a v & o r p l a t i n community ( P l a t e 31)
The n o r t h e r n p a r t o f t h e i s l a n d has a much l e s s d i s s e c t e d s u r f a c e and l a c k s shrubby growth. Along t h e seaward s i d e i t i s covered w i t h a dense mat o f Plumbago and Sarcostemma, b u t f u r t h e r i n l a n d and towards t h e n o r t h l a r g e a r e a s o f ground a r e b a r e , except f o r s c a t t e r e d g r a s s e s and sedges (Dactyloctenium, F i m b r i s t y l i s ) , weeds such a s Achyranthes, and long t r a i l e r s o f orange v i n e C a s s y t h a f i l i f o r m i s . I n c r e v i c e s and h o l e s it i s p o s s i b l e t o f i n d a few f l o w e r i n g Hedyotis s p . and S i d a p a r v i f o l i a , c h a r a c t e r i s t i c on Aldabra of t h e most exposed and almost u n v e g e t a t e d champignon o f t h e s o u t h e a s t c o a s t . This a r e a h a s probably been worked o v e r f o r phosphate, and t h e v e g e t a t i o n may be a p i o n e e r one o f t h e b a r e rock pavement which h a s r e s u l t e d .
S o l u t i o n - h o l e community
S o l u t i o n h o l e s i n t h e champignon now c o n t a i n t h e largest: t r e e s on Assumption, a p a r t from c o c o n u t s and C a s u a r i n a . I n t h e c e n t r e and south o f t h e i s l a n d Ficus nautarum i s c h a r a c t e r i s t i c o f s o l u t i o n h o l e s , a s on Aldabra: Dracaena r e f l e x a , s a i d t o occur i n h o l e s by F r y e r , was n o t s e e n by u s . No f e r n s have p r e v i o u s l y been recorded from Assumption, though Acrostichum aureum i s common i n shallow h o l e s a t t h e e a s t end o f Aldabra.
S h r i v e l l e d Acrostichum was found i n s e v e r a l h o l e s a t t h e n o r t h end o f Assumption i n 1967, t o g e t h e r w i t h , i n one c a s e , a f e r n n o t t h e n r e c o r d e d b u t s i n c e found on Aldabra, Nephrolepis b i s e r r a t a ( P l a t e 3 2 ) .
One h o l e n e a r t h e n o r t h p o i n t a l s o c o n t a i n s s e v e r a l t a l l t r e e s o f Ceriops t a g a l , though no mangroves have been p r e v i o u s l y r e c o r d e d from Assumption -hey do n o t occur on t h e c o a s t . Local i n f o r m a n t s s t a t e d t h a t t h i s was t h e o n l y s o l u t i o n h o l e w i t h mangroves. I n F r y e r ' s
manuscript j o u r n a l ( F r y e r 1908), however, h e r e c o r d s s e v e r a l such p i t s w i t h mature mangroves up t o 12 m t a l l , m o s t l y Bruguiera though i n one c a s e w i t h C e r i o p s . He was u n a b l e t o u n d e r s t a n d how mangroves came t o c o l o n i s e such i n l a n d h o l e s , a t l e a s t h a l f a m i l e from t h e s e a , and thought t h e y were f o r m e r l y more e x t e n s i v e . Most o f t h e s e i n l a n d
mangroves have probably d i s a p p e a r e d through b e i n g c u t f o r t i m b e r s i n c e 1908. One h o l e n o r t h of t h e s e t t l e m e n t i s now used a s a p o o l f o r k e e p i n g c a p t i v e t u r t l e s .
S e t t l e m e n t v e g e t a t i o n
Before permanent s e t t l e m e n t t h e r e were "a few c a s u a r i n a t r e e s , and i n one s p o t on t h e s h o r e t h r e e coconut palms" on t h e west c o a s t ( N i c o l l 1908, 1 0 7 ) ; S e b e r t Baty i n 1895 had found a t o t a l of s i x coconut palms [Berene 19001
. - .
A t t h e s i t e o f t h e f i r s t s e t t l e m e n t ( P l a t e 33) , ..
n o r t h e r n p a r t o f t h e west s h o r e , t h e r e i s a clump o f t a l l C a s u a r i n a , a coconut, two massive t r e e s of T e r m i n a l i a c a t a p p a , a p a t c h o f C a e s a l p i n i a bonduc, and s p r e a d i n n o u t o v e r t h e b a r e p l a t i n behind t h e beach a conspicuous a r e abf
~ ~ a v e . A t t h e p r e s e n t s e t t l e m e n t t h e r e i s a woodland b f mature C a s u a r i n a n e a r t h e manager's house, w i t h , t o t h e s o u t h , a coconutp l a n t a t i o n o f s e v e r a l hundred t r e e s . A t t h e s e t t l e m e n t i t s e l f t h e r e a r e c u l t i v a t e d t r e e s (Moringa o l e i f e r a , C a r i c a papaya) and o t h e r p l a n t s
(Catharanthus r o s e u s , Datura m e t e l , Gossypium h i r s u t u m , Ipomoea b a t a t a s , Leonotis n e p e t i f o l i a , Momordica c h a r a n t i a , P e d i l a n t h u s t i t h y m a l o i d e s , Solanum lycopersicum and Solanum nigrum), t o g e t h e r with weeds
(Achyranthes a s p e r a , Boerhavia e l e g a n s , Cleome s t r i g o s a , Dactyloctenium aegyptiwn, Enteropogon s e c h e l l e n s i s , Hypoestes a l d a b r e n s i s ,
S t a c h y t a r p h e t a j a m a i c e n s i s , Vernonia c i n e r e a ) . Between t h e s e t t l e m e n t and t h e s e a t h e r e i s a narrow hedge o f Scaevola t a c c a d a , with some T o u r n e f o r t i a a r g e n t e a and S u r i a n a m a r i t i m a , and a ground c o v e r o f
C a n a v a l i a r o s e a . Two i n t r o d u c t i o n s mentioned by Dupont i n 1907 were n o t seen i n 1967: Abrus p r e c a t o r i u s and A l b i z i a f a s t i g i a t a .
F l o r a
-
The f l o r a o f Assumption h a s n e v e r been p r o p e r l y worked up from t h e e a r l i e r c o l l e c t i o n s , though Dupont (1907) p u b l i s h e d a l i s t of s p e c i e s i n h i s t a b l e of i s l a n d p l a n t s , and Hemsley (1919) i n c l u d e d s p e c i e s c o l l e c t e d by F r y e r , Fox, Dupont and Thomasset i n h i s "Flora o f Aldabra". Gwynne
and Wood (1969) r e c o r d 8 s p e c i e s , f o u r of them s i g h t r e c o r d s . A l i s t of p l a n t s c o l l e c t e d i n 1967 i s given i n a l a t e r paper by Fosberg and
Renvoize (1970), and t h e f l o r a i s b e i n g i n c l u d e d i n t h e r e v i s i o n of t h e Aldabra f l o r a now being u n d e r t a k e n .
The p u b l i c a t i o n s o f Dupont and Hemsley l i s t about 63 s p e c i e s from Assumption; with t h e c o l l e c t i o n s made i n 1967, t h i s i s i n c r e a s e d t o about 100, o r roughly h a l f t h e number of s p e c i e s found on Aldabra.
Among t h e s p e c i e s conspicuously a b s e n t from t h e e a r l i e r r e c o r d s a r e t h e mangroves ( s p e c i e s of Avicennia, B r u g u i e r a , Rhizophora, Lumnitzera, S o n n e r a t i a , Ceriops and Xylocarpus, a l l found on A l d a b r a ) , Pandanus, and t h e f e r n s ; one mangrove and two f e r n s have s i n c e been c o l l e c t e d . Of t h e a d d i t i o n a l s p e c i e s c o l l e c t e d i n 1967, perhaps 16 r e p r e s e n t i n d i g e n o u s s p e c i e s p r e s e n t b u t u n c o l l e c t e d a t t h e time of t h e e a r l i e r v i s i t s ( e . g . s p e c i e s of Acalypha, Acrostichum, Boerhavia, C e r i o p s , Dactyloctenium, Euphorbia, Ipomoea, Launaea, N e p h r o l e p i s , Nostoc, Pennisetum, P o r t u l a c a , S i d a . Soohora. S c l e r o d a c t v l o n ~ . A t l e a s t 19 s p e c i e s c o l l e c t e d i n 1967,
' /,
o r o n e - f i f t h of t h e known f l o r a , r e p r e s e n t d e l i b e r a t e i n t r o d u c t i o n s o r weeds which have probably a r r i v e d s i n c e s e t t l e m e n t began i n 1908; s i x o f t h e s e have a l s b appeared a t Aldabra. These i n t r o d u c e d p l a n t s i n c l u d e s p e c i e s o f Agave, ~ a r i c a , C a t h a r a n t h u s , Datura, Ipomoea, L e o n o t i s ,
Momordica, Moringa, Solanum and T e r m i n a l i a .
Some i d e a of t h e c o n t r a s t between t h e f l o r a s o f Aldabra and Assumption, and t h e g r e a t e r changes i n t h e l a t t e r , can b e o b t a i n e d by comparing t h e c o l l e c t i o n s made s i x t y y e a r s ago on each w i t h t h o s e made i n 1966-67 ( t h i s comparison i n c l u d e s o n l y S t o d d a r t ' s c o l l e c t i o n s and n o t t h e more e x t e n s i v e c o l l e c t i o n s made on Aldabra by Fosberg and Renvoize):
Aldabra Assumption
Per c e n t t o t a l f l o r a r e c o r d e d
by Hemsley and e a r l i e r workers 46 2 8 Per c e n t recorded by b o t h Hemsley
and i n p r e s e n t c o l l e c t i o n 3 8 35 Per c e n t r e c o r d e d o n l y i n p r e s e n t
c o l l e c t i o n (new r e c o r d s ) 16 36 T o t a l number of s p e c i e s c.200 c.100
The comparison i s o n l y approximate, f o r t h e Assumption f l o r a i s s t i l l t o be p r o p e r l y c o l l e c t e d and t h e A l d a b r a c o l l e c t i o n s o f 1966-67 were s m a l l and p r e l i m i n a r y , b u t i t i s c l e a r t h a t c o n s i d e r a b l e changes have t a k e n p l a c e i n t h e f l o r a a s w e l l a s i n t h e v e g e t a t i o n o f Assumption s i n c e s e t t l e m e n t began.
Of t h e s p e c i e s l i s t e d by Hemsley (1919), t h r e e have been d e s c r i b e d a s endemic (Panicum a s s u m p t i o n i s S t a p f , E r i o c h l o a s u b u l i f e r a S t a p f , Stenotaphrum clavigerum S t a p f ) , and twenty c o u l d b e c l a s s e d a s " r e g i o n a l endemics". S i n c e t h e new r e c o r d s a r e mainly cosinopolitan weeds and
c u l t i v a t e d p l a n t s , t h e f l o r a is changing from one t y p i c a l o f t h e e l e v a t e d r e e f i s l a n d s of t h e southwest I n d i a n Ocean t o one dominated by common t r o p i c a l s p e c i e s o f no p a r t i c u l a r r e g i o n a l a f f i n i t y .
Marine fauna
The Green T u r t l e Chelonia mydas was f o r m e r l y abundant on Assumption.
Baty ( i n Bergne 1900) and N i c o l l (1908) r e p o r t e d them i n g r e a t numbers c l o s e t o t h e s h o r e , and a l s o n e s t i n g . Fryer found them p l e n t i f u l , b u t s a i d t h a t it was no longer p o s s i b l e t o t a k e up t o two hundred i n a n i g h t a s had once been t h e p r a c t i c e ( F r y e r 1910, 2 6 3 ) . Numbers have d e c l i n e d c a t a s t r o p h i c a l l y , and though t u r t l e s t i l l come a s h o r e a t one o r two p l a c e s on t h e e a s t c o a s t t o l a y , f o r s e v e r a l y e a r s i t h a s had t o b e
p r o h i b i t e d t o t a k e them o r t h e i r eggs anywhere on Assumption. There h a s , however, been no means o f e n f o r c i n g t h i s p r o h i b i t i o n among t h e i s l a n d ' s l a b o u r e r s . L i t t l e e l s e i s known o f t h e marine fauna; J . L . B . Smith c o l l e c t e d f i s h a t Assumption i n 1954, and a few r e c o r d s have appeared i n h i s r e v i s i o n s of t h e I n d i a n Ocean f i s h fauna (Smith 1955a, 1955b, 1956a,
1956b).
Land f a u n a o t h e r t h a n b i r d s
The o n l y indigenous mammal a t Assumption i s an i n s e c t i v o r o u s b a t Taphozous m a u r i t i a n u s c o l l e c t e d by Fryer i n October 1908 ( S c o t t 1914,
1 6 3 ) . The f r u i t - b a t P t e r o p u s , found on Aldabra, i s a b s e n t . The indigenous land r e p t i l e s f o r m e r l y i n c l u d e d t h e Giant Land T o r t o i s e
Geochelone s p . , which, however, became e x t i n c t b e f o r e e v e r b e i n g r e c o r d e d a l i v e , a s f a r a s can be a s c e r t a i n e d . Fryer found t h e remains o f two i n a s o l u t i o n h o l e i n 1.908, and Honegger found eggs i n a guano p i t on 1964.
The geckos Phelsuma a b b o t t i a b b o t t i and Hemidactylus n ~ e r c a t o r i u s , and t h e s k i n k Ablepharus b o u t o n i i , a r e a l s o indigenous (Boulenger 1911);
both Hemidactylus and Ablepharus were c o l l e c t e d on t h e h i g h dunes i n 1967. A l l t h r e e s p e c i e s a r e found on Aldabra. The l a n d C r u s t a c e a i n c l u d e Birgus l a t r o , v e r y common i n 1906 ( N i c o l l 1908, 112) and s t i l l e x i s t i n g . 65 s p e c i e s o f i n s e c t s have been r e c o r d e d , mainly c o l l e c t e d by F r y e r and Dupont, and t h e l i t e r a t u r e on t h e s e e a r l i e r c o l l e c t i o n s i s
keyed i n Table 14. There was no o p p o r t u n i t y t o c o l l e c t i n s e c t s i n 1967, though members o f t h e Odonata were conspicuous. Blackman and Pinhey
(1967) review t h i s group on w e s t e r n I n d i a n Ocean i s l a n d s , w i t h mention of Assumption.
Land ( i n c l u d i n g s h o r e ) b i r d s
Birds form t h e b e s t known element i n t h e Assumption land f a u n a , and a r e a l s o t h e group a p p a r e n t l y most a f f e c t e d by guano mining. I n
connection with t h e f o l l o w i n g a c c o u n t , we a r e g r a t e f u l t o P r o f e s s o r Charles G . S i b l e y and Mrs Eleanor H . S t i c k n e y f o r t h e l o a n from t h e
Peabody Museum o f N a t u r a l H i s t o r y , Yale U n i v e r s i t y , of m a t e r i a l c o l l e c t e d by Hartman i n 1957.
Group
O r t h o p t e r a Dermaptera Hemipt e r a
L e p i d o p t e r a
Table 14. I n s e c t s r e c o r d e d from Assumption by t h e Percy Sladen Expedition
C o l e o p t e r a
Hymenoptera
D i p t e r a Odonata
Number o f s p e c i e s 10
Reference
B o l i v a r (1912, 1924) Burr (1910)
D i s t a n t (1913, 1917) F l e t c h e r (1910), F r y e r
(1912), Mampson (1908) A u r i v i l l i u s ( 1 9 2 2 ) , Champion (1914), Gebien 1922, S c o t t (1912, 1926) Cockerel1 119121. , .
Morley (1912), T u r n e r (1911)
Lamb (1922, 1 9 1 4 ) , S c o t t (1914)
Campion (1913)
R e s i d e n t s
There a r e f i v e l a n d b i r d s which b r e e d l o r d i d s o f o r m e r l y ) on Assumption, with f o u r more which may do s o . These a r e :
Dryolimnas c u v i e r i W h i t e - t h r o a t e d R a i l S t r e p t o p e l i a p i c t u r a t a Malagasy T u r t l e d o v e
Centropus t o u l o u Malagasy Coucal
N e c t a r i n i a sovimanga Souimanga Sunbird
Corvus a l b u s P i e d Crow
p l u s
Ardea c i n e r e a E g r e t t a g a r z e t t a Bubulcus i b i s B u t o r i d e s s t r i a t u s
Grey Heron L i t t l e Egret C a t t l e E g r e t
L i t t l e Green Heron
A l l o f t h e s e s p e c i e s a l s o b r e e d on Aldabra, which h a s a t l e a s t s e v e n t e e n b r e e d i n g land b i r d s . The f o l l o w i n g b r e e d i n g Aldabra l a n d b i r d s have n e v e r been recorded on Assumution:
T h r e s k i o r n i s a e t h i o p i c a s a c r e d I b i s
Falco newtoni Malagasy K e s t r e l
A l e c t r o e n a s s g a n z i n i Comoro Blue Pigeon Caprimulgus m a d a g a s c a r i e n s i s Malagasy N i g h t j a r H v u s i o e t e s m a d a ~ a s c a r i e n s i s " M a l a ~ a s v " Bulbul i e ' s i l i a s aldabranus Aldabra T s i k i r i t y
D i c r u r u s aldabranus Aldabra Drongo
Zosterops maderaspatana Malagasy White-eye
Foudia eminentissima Red-headed F o r e s t Fody
Nor has t h e Barn O w l Tyto a l b a been r e c o r d e d from Assumption. -- I t c e r t a i n l y o c c u r r e d (and p r o b a b l y b r e d ) i n t h e p a s t on Aldabra, b u t
appears no l o n g e r t o e x i s t t h e r e . The Malagasy C i s t i c o l a c h e r i n a , which Benson found p l e n t i f u l on Menai and Wizard I s l a n d s (Cosmoledo A t o l l ) and on Astove i n March 1968, i s unkown on Assumption o r Aldabra.
The Assumption s u b s p e c i e s o f t h e W h i t e - t h r o a t e d R a i l was d i s c o v e r e d by Abbott i n 1892 and named Dryolimnas a b b o t t i by Ridgway (1894a, 7 4 ) .
Fryer ( i n MS) i n 1908 found " p l e n t y o f t h e R a i l D . a b b o t t i which was v e r y tame and v e r y common". Both Abbott i n 1 8 9 2 a n d N i c o l l i n 1906
found it abundant. "They were found on a l l p a r t s o f t h e i s l a n d , e x c e p t on t h e swnmit of t h e sandy h i l l on t h e windward s i d e " ( N i c o l l 1908, 109).
I n s p i t e o f t h e l a r g e numbers, N i c o l l f e a r e d t h a t i n t r o d u c e d r a t s might l e a d t o i t s e x t i n c t i o n by p r e d a t i o n o f eggs (1908, 111). I t d i d d u l y become e x t i n c t some t i m e between t h e e s t a b l i s h m e n t of t h e s e t t l e m e n t i n
1908 and V e s e y - F i t z G e r a l d ' s v i s i t i n 1937, undoubtedly a s a r e s u l t o f c a t c h i n g f o r food, d e s t r u c t i o n o f h a b i t a t , and p r e d a t i o n by i n t r o d u c e d c a t s and r a t s . I t was c o n s p e c i f i c w i t h Dryolimnas c . c u v i e r i , o f
Malagasy, a s i s t h e Aldabra form. I t a m e a r s n o t A
to
have l o s t t h e power o f f i i g h t s o c o m p l e t e l y a s - D . - c . a l d a b r a n u s : s e e t h e wing-lengths i n Benson (1967, 7 4 ) .The t u r t l e d o v e S t r e p t o p e l i a p i c t u r a t a was n o t d e f i n i t e l y r e c o r d e d by Abbott i n 1892 ( s e e Ridgway 1895, 522, under T u r t u r a l d a b r a n u s ) , b u t was s o by N i c o l l (1906, 693; 1908, 109, under T. a s s u m p t i o n i s ) . I t was
" q u i t e common" and " e x t r a o r d i n a r i l y tame" a t t F e t i m e o f N i c o l l ' s v i s i t , when i t n e s t e d i n t h e branches o f Hibiscus (?) b u s h e s . I t was mentioned by Fryer i n 1908, b u t n o t by Vesey-FitzGerald i n 1937, and h a s n o t been s e e n s i n c e . I t was p r o b a b l y e x t i r p a t e d by t h e l a b o u r e r s , a g a i n f o r food. I t seems t o have o n l y d i f f e r e d from t h e Aldabra p o p u l a t i o n i n b e i n g a l i t t l e l a r g e r (Benson 1967, .75-79). T h i s i s s u p p o r t e d by wing-
l e n g t h s o f r e c e n t Aldabra m a t e r i a l , f o u r males measuring 166, 167, 169, 170, and s i x females 155, 157, 158, 160, 160, 163 nun.
The c o u c a l Centropus t o u l o u was c o l l e c t e d by Abbott (C. i n s u l a r i s i n Ridgway 1895, 522-523), and was n o t e d a s common and t a n g by N i c o l l
(1906, 494, a s C . a s s u m p t i o n i s ) and by F r y e r ( i n MS). Vesey-FitzGerald (1940, 487) s a w o n e i n 1937. But i t i s n o t mentioned by Hartman (1958), n e i t h e r d i d G a p e r s e e it i n 1964 o r 1965, n o r Benson i n 1967, n o r
F r a z i e r i n 1968. Wright i n 1967 t h o u g h t h e saw one b u t was n o t s u r e . I t may a l s o be e x t i n c t , e x t i r p a t e d by t h e l a b o u r e r s f o r food. According t o Benson (1967, 8 0 - 8 1 ) , it i s ( o r was) o n l y p o s s i b l y d i s t i n g u i s h a b l e from - C .
-
t . i n s u l a r i s of Aldabra by i t s s l i g h t l y s h o r t e r t a i l . The f o l l o w i n g a r e measurements i n mm o f f u r t h e r a d u l t Aldabra specimens:Wing T a i 1
dd 149 150 2 3 2 3
9 165 250
The s m a l l e r male t a i l - l e n g t h i n d i c a t e s an o v e r l a p i n f i g u r e s f o r i n s u l a r i s and a s s u m p t i o n i s , and t h e l a t t e r name i s r e a l l y no l o n g e r worth m a i n t a i n i n g .
The s u n b i r d N e c t a r i n i a sovimanga i s s t i l l r e l a t i v e l y f l o u r i s h i n g , i n no apparent immediate danger o f e x t i n c t i o n , even though i t s numbers have probably been g r e a t l y reduced by d e s t r u c t i o n of t h e o r i g i n a l h a b i t a t . On t h e morning o f 16 September Benson counted e i g h t males,
f o u r females and s i x unsexed b i r d s on t h e s o u t h - e a s t s i d e o f t h e i s l a n d , i n t h e mixed s c r u b community, and i n t h e a f t e r n o o n 43 males and 26
females i n t h e west c o a s t sand beach community, a l s o a few i n Casuarina t r e e s a t t h e s i t e of t h e o l d s e t t l e m e n t n e a r t h e northwest c o r n e r o f t h e i s l a n d . F r a z i e r found s u n b i r d s s i n g i n g i n t h e t r e e s a t t h e p r e s e n t s e t t l e m e n t . A l l males observed a m e a r e d t o be i n f u l l b r e e d i n e d r e s s . A
-
Feeding was n o t i c e d a t flowers o f
Agave
and T o u r n e f o r t i a a r g e n t e a .Although Vesey-FitzGerald (1940, 487) r e p o r t e d it a s r a r e , Hartman (1958) found i t common, and it i s t h e most p l e n t i f u l t r u e land b i r d on Aldabra.
I t i s p o s s i b l e t h a t competition from N e c t a r i n i a h a s excluded t h e white- eye Zosterops maderaspatana from Assumption, which, u n l i k e Aldabra, may n o t be l a r g e enough f o r both (Serventy 1951). N e v e r t h e l e s s b o t h have been r e c o r d e d from o t h e r small i s l a n d s - - G l o r i o s a , Astove, and Menai I s l a n d i n Cosmoledo. N . s . a b b o t t i i s a v a l i d s u b s p e c i e s , endemic t o Assumption (Benson 1967, g4-86). This i s confirmed by f u r t h e r m a t e r i a l
from Aldabra, Assumption, Cosmoledo and Astove, t h e s u b s p e c i e s on b o t h t h e l a t t e r two i s l a n d s b e i n g
- -
N . s . buchenorum.The crow Corvus a l b u s was c o l l e c t e d by Abbott i n 1892 (Ridgway 1895, 532, under C . s c a p u l a t u s ) . N i c o l l (1906, 693; 1908, 109) r e c o r d e d s m a l l numbers, a n a found s e v e r a l empty n e s t s " b u i l t a t t h e t o p s o f t h e t a l l e s t t r e e s on t h e i s l a n d " . He a l s o n o t e d i t a s "extremely wild". Vesey- F i t z G e r a l d (1940, 588), however, c o n s i d e r e d it was only a v i s i t o r .
"About 25" were seen i n 1964 (Bourne 1966); and Gaymer recorded about
"two dozen" i n t h e same y e a r . Benson saw 10 on 15 September 1967 and Morton Boyd a t o t a l of 15 on t h e same day: it was seen a t t h e s e t t l e m e n t , i n Casuarina t r e e s a t t h e o l d s e t t l e m e n t s i t e , and over t h e s o u t h e a s t dunes. F r a z i e r saw none i n 1968. Probably i t does s t i l l breed on
Assumption, a s r e c e n t l y d e f i n i t e l y e s t a b l i s h e d f o r Aldabra. Breeding may t a k e p l a c e only a t i n f r e q u e n t i n t e r v a l s , and s o can be e a s i l y overlooked.
Of t h e p o s s i b l y b r e e d i n g s h o r e b i r d s , Ardea c i n e r e a and E g r e t t a g a r z e t t a , both c o l l e c t e d by N i c o l l (1906, 695-696, t h e l a t t e r under Demiegretta s a c r a ) , have n o t o t h e r w i s e been r e c o r d e d , except t h a t Dupont
(1907) l i s t s t h e former. P o s s i b l y t h e y no l o n g e r e x i s t on Assumption, though i t i s u n l i k e l y t h a t they have been molested t o t h e same e x t e n t
(except a t p o s s i b l e b r e e d i n g s i t e s ) a s t h e t u r t l e d o v e and c o u c a l d i s c u s s e d above. Bubulcus i b i s was seen by Gaymer i n 1964, and t h e r e was a f l o c k o f about 60 i n l a n d , j u s t s o u t h o f t h e s e t t l e m e n t , i n 1967.
I t s s t a t u s on Assumption i s q u i t e u n c e r t a i n .
B u t o r i d e s s t r i a t u s , recorded by N i c o l l (1906, 696, under B .
c r a w f o r d i ) , and l i s t e d by Dupont (1907, under B . a t r i c a p i l l u s ) , was s e e n by Gaymer i n 1964, by Benson on t h e s o u t h e a s t Fhore a t low w a t e r ( t h r e e
a d u l t s , one immature) and i n l a n d ( t h r e e a d u l t s ) i n 1967, and by F r a z i e r on t h e southwest c o a s t i n 1968. Assumption i s t h e t y p e - l o c a l i t y of
N i c o l l ' s
-
B .-
s . c r a w f o r d i , only o t h e r w i s e r e c o r d e d from Aldabra (Benson (1967, 6 7 ) . A d d i t i o n a l m a t e r i a l , now i n t h e B r i t i s h Museum ( N a t u r a l l i i s t o r y ) , i s a v a i l a b l e from Aldabra, and A . D . Forbes-Watson h a s k i n d l y donated on b e h a l f o f t h e N a t i o n a l Museum of Kenya, N a i r o b i , a specimen c o l l e c t e d by I . S . C . P a r k e r i n t h e Amirante I s l a n d s , on t h e r e e f between Darros and S t Joseph (S025'S, 5 3 ' 1 8 ' ~ ) , on 23 September 1967.Wing-lengths i n mm o f t h i s m a t e r i a l a r e :
Aldabra dd 159 165
99
156 158 162 Amirante I s l a n d s9
169One male and one female from Aldabra have t h e s i d e s o f t h e neck, c h e s t and abdomen washed with brown, b u t t h e o t h e r specimens l a c k t h i s wash.
I t may be t h a t o n l y t h e l a t t e r a r e completely a d u l t , t h e d i f f e r e n c e t h u s b e i n g due t o age r a t h e r t h a n s e x , c o n t r a Benson (1967, 6 8 ) . I t i s
i m p o s s i b l e t o s e p a r a t e t h e Amirante specimen from t h o s e from Aldabra on c o l o u r , and on p r e s e n t evidence c r a w f o r d i must b e r e g a r d e d a s e x t e n d i n g n o r t h t o t h e Amirantes. P o s s i b l y Amirante b i r d s a r e a l i t t l e l a r g e r , s e e a l s o f u r t h e r f i g u r e s i n Benson (1967). T h i s i s a l s o suggested by weights, t h e Amirante specimen b e i n g t h e h e a v i e s t . Those whose wing- l e n g t h s were given above weighed r e s p e c t i v e l y 164, 158, 168, 1 6 3 , 177, 180 g. T h i s r e c e n t Aldabra m a t e r i a l , c o l l e c t e d i n 1968, i s n o t markedly p a l e r grey below t h a n i n any specimen o f B. s . r h i z o p h o r a e , whether
c o l l e c t e d a decade o r a c e n t u r y ago, and T h e t w o s u b s p e c i e s may o n l y b e d i s t i n g u i s h a b l e on s i z e . I t would seem t h a t t h e t y p e o f c r a w f o r d i and t h e a d u l t male from Aldabra examined by Benson (1967, 6 7 ) , s o p a l e grey below, a r e e x c e p t i o n a l i n d i v i d u a l s .
Migrants
The f o l l o w i n g a r e recorded from Assumption:
Ardeola i d a e
-
One s e e n by Benson t o f l y o n t o t h e i s l a n d , from t h e d i r e c t i o n o f Aldabra, a t 0800 h o u r s on 16 ~ e L t e m b e r 1967. I t was thought t o b e
-
t h i s s p e c i e s , now known t o o c c u r on Aldabra, whereas A.
-
r a l l o i d e s i s n o t . S q u a t a r o l a s q u a t a r o l aTwo s e e n on t h e s o u t h e a s t c o a s t i n 1967.
C h a r a d r i u s l e s c h e n a u l t i i
L i s t e d by Dupont (1907, under A e g i a l i t i s g e o f f r o y i ) ; t h r e e s e e n i n 1967.
Numenius phaeopus
L i s t e d by Dupont (1907) ; two s e e n i n 1967.
Numenius a r q u a t a
L i s t e d by Dupont (1907).
T r i n g a n e b u l a r i a
L i s t e d by Dupont (1907, under Totanus g l o t t i s ) ; two seen i n 1967.
A c t i t i s h r p o l e u c o s
L i s t e d by Dupont (1907)
A r e n a r i a i n t e r p r e s
L i s t e d by Dupont (1907); 100 seen i n March 1964 (Bourne 1966);
f i v e seen i n 1967.
C r o c e t h i a a l b a
One seen i n 1967.
E r o l i a minuta
L i s t e d by Dupont (1907).
Dromas a r d e o l a
L i s t e d by Dupont 11907); 40 s e e n i n March 1964 (Bourne 1966);
one seen on t h e s o b t h e i s t s h o r e
i n
1967.Hirundo r u s t i c a
On 13 December 1957 Hartman (1958) saw "an u n i d e n t i f i e d swallow, b l a c k above, w h i t e below, and w i t h a l o n g , f o r k e d t a i l " , " i n f l i g h t o v e r t h e sand dunes". I t was very p r o b a b l y t h i s s p e c i e s , f o r which Benson
(1967, 95) q u o t e s one s i g h t i n g f o r Malagasy i n J a n u a r y , while a number were seen on Aldabra i n March 1968.
Other m i g r a n t s must occur o c c a s i o n a l l y on Assumption. Thus among s h o r e b i r d s , E r o l i a t e s t a c e a i s p l e n t i f u l on Aldabra, and some 14 s p e c i e s o f p a l a e a r c t i c t r u e land b i r d s have by now been found t h e r e .
Sea b i r d s
Sea b i r d s were n o t common i n 1967, and have c e r t a i n l y g r e a t l y d e c r e a s e d i n numbers d u r i n g t h e l a s t s i x t y y e a r s . I t i s p r o b a b l e t h a t few now n e s t on Assumption. The f o l l o w i n g s p e c i e s have been r e c o r d e d :
-
Phaethon r u b r i c & d a
C o l l e c t e d bv Abbott (Ridewav 1895. 5221. who found i t b r e e d i n e
. - -
i n dense t h i c k e t s o r knder a bush, anh by ~ I c o i i ' i i 9 0 6 , 6 9 3 ) . Not s e e n i n 1967. Loustau-Lalanne (1963, 2 1 , 23) c o n s i d e r s i t c o n f i n e d t o
Assumption, b u t t h i s i s n o t c o r r e c t . Thus Benson (1967, 99) q u o t e s r e c o r d s from Aldabra, where i t b r e e d s .
-
P. l e p t u r u s h a s n e v e r been recorded from Assumption.S u l a a b b o t t i
C o l l e c t e d by Abbott (Ridgway 1893, 599; 1895, 520-522), who s t a t e d t h a t "a few" b r e e d . According t o F r y e r (1911, 433) it " i n h a b i t s t h e l a r g e dune, n e v e r descending t o low p a r t s o f t h e i s l a n d . " I t h a s n o t been r e c o r d e d s i n c e , and Vesey-FitzGerald (1941, 52) s a y s i t was e x t i r p a t e d i n 1926; t h e s p e c i e s now o n l y b r e e d s on Christmas I s l a n d
( I n d i a n Ocean). Gibson-Hill (1950) h a s v e r y f u l l y d i s c u s s e d u n c e r t a i n - t i e s i n t h e e a r l i e r r e c o r d s . The two specimens c o l l e c t e d by F r y e r on Assumption, and examined by G i b s o n - H i l l , a r e s t i l l e x t a n t i n t h e U n i v e r s i t y Museum o f Zoology, Cambridge. The s t a t e m e n t by Loustau- Lalanne (.1963, 23) i n r e g a r d t o t h e Red-footed Booby S u l a s u l a
--
i s p r e - sumed t o b e r e a l l y i n t e n d e d t o a p p l y t o S . a b b o t t i , though u n f o r t u n a t e l y i t i s more than "very n e a r e x t i n c t i o n " o n Assumption.S u l a d a c t y l a t r a . (syn. S . cyanops)
Noted by Abbott ( K i d p a y 1895, 520) t o b r e e d on b a r e ground on t h e sand dunes; c o l l e c t e d by N i c o l l (1906, 6 9 7 ) . Probably no l o n g e r b r e e d i n g i n 1937 (Vesey-FitzGerald 1941, 521) b u t "a few" s e e n in-1964
(Bourne 1966). Not seen i n 1967. S e b e r t Baty i n 1895 found a "camp of boobies", s p e c i e s n o t s p e c i f i e d , on guano 600 y a r d s n o r t h e a s t o f t h e b i g dune, and boobies i n t r e e s ( S u l a s u l a
--
?) a l l o v e r t h e i s l a n d (Bergne 1900).S u l a s u l a
--
Recorded b r e e d i n g by N i c o l l (1906, 6 9 7 ) . Four s e e n i n 1967 F r e g a t a minor (syn. F. a q u i l a )~ e c o r d e d by N i c c l l (1906, 692) and l i s t e d by Dupont (1907).
Not seen i n 1967, b u t R. Hughes saw a female i n March 1968.
F r e g a t a a r i e l
A group o f f o u r males and seven females, a l l a p p a r e n t l y a d u l t , seen s o a r i n g over t h e s o u t h e a s t c o a s t i n 1967.
S t e r n a f u s c a t a
15-20 s e e n by J . F r a z i e r o f f t h e west c o a s t i n March 1968.
S t e r n a a l b i f r o n s
L i s t e d by Dupont (1907, under both S . minuta and S. balaenarum).
About t h i r t y probably t h i s s p e c i e s seen i n
arch
1964 ( ~ o u r n e 1966).S t e r n a sumatrana
Three r e c o r d e d i n March 1964 (Bourne 1966), and one f l o c k of t e n , a n o t h e r of f o u r , on t h e s o u t h e a s t c o a s t i n 1967
Thalasseus b e r g i i
L i s t e d by Dupont (1907, under b o t h " S t e r n a B e r s t e i n i " and
"Sterna Bergi").
Anous s t o l i d u s
L i s t e d by Dupont (1907).
Gygis a l b a
--
C o l l e c t e d by N i c o l l (1906, 696), l i s t e d by Dupont (1907). One s e e n i n March 1964 (Bourne 1966). On 16.September 1967 Benson saw one l o t of t e n , f o u r each o f two, and one s i n g l e b i r d , and E . Wright a t o t a l o f about 20. J . F. Peake found t h r e e probably b r e e d i n g - i n a s o l u t i o n h o l e . F r a z i e r saw 4-5 o f f t h e west c o a s t on 31 J u l y 1968.I n t r o d u c e d animals
Rats were abundant by t h e t i m e o f N i c o l l ' s v i s i t ( b e f o r e s e t t l e m e n t began), and were a l r e a d y d e s t r o y i n g b i r d s ' e g g s . Goats were i n t r o d u c e d
"many y e a r s " b e f o r e A b b o t t ' s v i s i t i n 1893, a c c o r d i n g t o him from Europa I s l a n d i n t h e Mozambique Channel (Abbott 1893, 763). According t o Bergne (1901) g o a t s were i n t r o d u c e d by H.M.S.
-
Wasp, Captain B i d e n f i e l d , i n 1867, a crew member on t h a t o c c a s i o n l i v i n g on Astove when Bergne v i s i t e d it i n 1901. S e b e r t Baty gave t h e number o f g o a t s a s 300-400 i n 1895 (Bergne 1900). Dupont (1907, 12) gave t h e d a t e of i n t r o d u c t i o n a s c . 1887 and t h e number i n 1906 a s " s e v e r a l thousands". N i c o l l (1908, 112) found twenty, v e r y w i l d , n e a r t h e f o o t o f t h e dunes. Vesey-FitzGerald (1942) d i d n o t mention them and G a p e r thought t h e y were e x t i n c t i n 1964. We saw none i n 1967, though we were t o l d t h a t some s t i l l e x i s t e d i n t h e n o r t h . Dupont was s o impressed by t h e g o a t s a s a food r e s o u r c e t h a t he s u g g e s t e d t h e i n t r o d u c t i o n o f r a b b i t s and h a r e s (Dupont 1907, 1 3 ) . Dogs, c a t s and chickens were s e e n i n 1967.S e t t l e m e n t and E x p l o i t a t i o n
S e t t l e m e n t began i n June 1908, and by F r y e r ' s a r r i v a l i n September t r a c k s had been c u t through t h e bush i n s e v e r a l d i r e c t i o n s . The f i r s t s e t t l e m e n t was i n t h e n o r t h e r n p a r t o f t h e west bay, and l a r g e r a i n w a t e r t a n k s were c o n s t r u c t e d t h e r e i n 1910. Both c o n t a i n e d e x c e l l e n t w a t e r i n 1967. A t a d a t e unknown t h e s e t t l e m e n t was t r a n s f e r r e d t o t h e s o u t h end o f t h e bay, where t h e r e i s now a manager's house and g a r d e n , and a l i n e o f l a b o u r e r s ' h u t s ( P l a t e 3 4 ) . There i s a s h o r t j e t t y , a b o a t house, and t o t h e n o r t h a small cemetery. On t h e e a s t c o a s t t h e r e a r e two s m a l l f i s h i n g shacks on t h e dunes.
Between 1926 and 1945, 161,000 t o n s o f guano were e x p o r t e d , t o g e t h e r w i t h an unknown amount b e f o r e 1926. A f t e r 1945 t h e l e a s e l a p s e d and e x p l o i t a t i o n ceased i n 1948; b u t w i t h t h e renewal o f t h e l e a s e i n 1955 mining began a g a i n . A mechanical c r u s h e r and l i g h t r a i l w a y ( P l a t e 35) have been i n s t a l l e d . Baker (1963) e s t i m a t e d r e s e r v e s a t 160,000 t o n s
f o l l o w i n g h i s survey i n 1960, mostly i n s o l u t i o n h o l e s . Because o f t h e s h a r p d e c l i n e i n t h e p r i c e o f guano, p r o d u c t i o n was a t a s t a n d s t i l l i n 1967, and mounds o f guano s t o o d a t t h e s e t t l e m e n t u n a b l e t o be s h i p p e d . Assumption i s l e a s e d j o i n t l y w i t h Aldabra and Cosmoledo by M H. Savy r o f ~ a h ; , f o r t h i r t y y e a r s from 1955 ( S t o d d a r t and Wright 1967, 48-50).
Unlike Aldabra, i t s t i l l forms p a r t of t h e Colony of S e y c h e l l e s , and h a s n o t been i n c o r p o r a t e d i n t h e B r i t i s h I n d i a n Ocean T e r r i t o r y .
Summary and Conclusions
A f t e r s i x t y y e a r s of i n t e n s i v e e x p l o i t a t i o n and a p r e v i o u s c e n t u r y o f more c a s u a l i n t e r f e r e n c e , Assumption has now l o s t many o f t h e f a u n a l and f l o r a l elements which formerly c h a r a c t e r i s e d t h e e l e v a t e d r e e f i s l a n d s o f t h e southwest I n d i a n Ocean. There i s no doubt t h a t a t t h e time o f s e t t l e m e n t i n 1908 a number of i r r e v e r s i b l e changes had taken p l a c e , p a r t i c u l a r l y t h e d i s a p p e a r a n c e o f t h e Giant Land T o r t o i s e . The T o r t o i s e p o p u l a t i o n on s o small an i s l a n d must c l e a r l y have been more v u l n e r a b l e t o cropping f o r food d u r i n g t h e l a t e e i g h t e e n t h and e a r l y n i n e t e e n t h c e n t u r i e s t h a n on t h e much l a r g e r i s l a n d of Aldabra. The p r e s e n c e o f i n t r o d u c e d g o a t s must have i n i t i a t e d v e g e t a t i o n changes, and e a r l y r e p o r t s mention t h e wide d i s t r i b u ' i i o n o f Plumbago.
Major v e g e t a t i o n and f l o r i s t i c changes, however, followed t h e beginning o f phosphate mining, i n which v e g e t a t i o n was removed and t h e phosphate s c r a p e d from t h e s u r f a c e of t h e ground, l e a v i n g a s t e r i l e rock s u r f a c e f o r new c o l o n i s a t i o n . Many o f t h e s p e c i e s common i n Mixed Scrub on Aldabra and p o s s i b l y formerly p r e s e n t on Assumption appear now t o be a b s e n t on t h e l a t t e r , and t h e i r p l a c e has been taken by weeds
such a s Plumbago, Sarcostemma and Cassy.tha, and escapes such a s Gossypim.
A l l o f t h e s e s p e c i e s a r e r a r e on Aldabra e x c e p t c l o s e t o t h e s e t t l e m e n t where man h a s a c t i v e l y i n t e r f e r e d with indigenous v e g e t a t i o n . The o n l y a r e a s a p p a r e n t l y u n a f f e c t e d by t h e s e changes on Assumption a r e t h e h i g h
dunes and t h e windward perched b e a c h , w i t h t h e i r t y p i c a l v e g e t a t i o n of .
Sporobolus, S c l e r o d a c t y l o n , S c a e v o l a , S u r i a n a and T o u r n e f o r t i a , a l l c h a r a c t e r i s t i c o f similar h a b i t a t s on Aldabra. Lack o f a c t i v e d i s t u r b a n c e and t h e extreme environmental c o n d i t i o n s have p r o b a b l y r e s t r i c t e d i n v a s i o n s i n t h e s e h a b i t a t s . I n t h e f l o r a a s a whole,
indigenous elements a r e p o s s i b l y b e i n g r e p l a c e d by common weeds, many of p a n - t r o p i c a l d i s t r i b u t i o n , and c u l t i v a t e d p l a n t s , b u t f u r t h e r d a t a on t h e s e p r o c e s s e s a r e r e q u i r e d .
With major v e g e t a t i o n changes and p r o b a b l e continuous p r e d a t i o n , t h e b i r d fauna h a s changed c o n s i d e r a b l y s i n c e 1908. The endemic r a i l Dryolimnas c u v i e r i a b b o t t i h a s c e r t a i n l y become e x t i n c t , t h e l o c a l p o p u l a t i o n of t h e t u r t l e d o v e S t r e p t o p e l i a p i c t u r a t a p o s s i b l y s o t o o . Of t h e s h o r e b i r d s , Ardea c i n e r e a and E g r e t t a g a r z e t t a may no l o n g e r o c c u r . Changes i n t h e s e a b i r d p o p u l a t i o n have been c o n s i d e r a b l e . Though a few S u l a s u l a and S . d a c t y l a t r a have been seen i n r e c e n t y e a r s , t h e booby
--
b r e e d i n g colonyes over t h e n o r t h e r n h a l f o f t h e i s l a n d have d i s a p p e a r e d . A b b o t t ' s Booby S u l a a b b o t t i-
i s now e x t i n c t on Assumption, and b r e e d s only on faraway Christmas I s l a n d . None o f t h e o t h e r e i g h t recorded s p e c i e s o f s e a b i r d i s now d e f i n i t e l y known t o b r e e d , though--
Gygis a l b a p r o b a b l y does s o . On t h e o t h e r hand, t h e endemic s u n b i r d N e c t a r i n i a sovimanga a b b o t t i , t h e crow Corvus a l b u s , and m i g r a n t s g e n e r a l l y , a r e p r o b a b l y l i t t l e a f f e c t e d by changes on t h e i s l a n d .S i n c e s e t t l e m e n t began t h e l a r g e b r e e d i n g grounds on Assumption of t h e Green T u r t l e have been l a r g e l y abandoned, and though t h i s d e c l i n e appears t o be common throughout t h e southwest I n d i a n Ocean i t h a s been e s p e c i a l l y c a t a s t r o p h i c on Assumption.
Assumption t h u s p r o v i d e s an extreme example o f e c o l o g i c a l change brought about by human s e t t l e m e n t and e x p l o i t a t i o n . S i n c e e x p l o i t a t i o n
depends on t h e maintenance of an economic p r i c e f o r phosphate, i t i s p o s s i b l e t h a t t h e v e n t u r e w i l l become uneconomic and t h e s e t t l e m e n t could be abandoned. I f t h i s o c c u r s i t w i l l be u s e f u l t o observe t h e p r o g r e s s o f e c o l o g i c a l change i n t h e f u t u r e , a s p a r t of t h e Royal S o c i e t y ' s c o n t i n u i n g programme a t Aldabra.
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