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NUMBER 89 35
over the stapedio-temporal circulation; Bour, 1985), which indicates
that their common ancestor evolved independently
from the Mauritian populations before it was subjected to the
environmental constraints that led to the present-day situation.
On the other hand, the Reunion land-tortoise, although immediately
identifiable by its extremely robust dentary and maxillary
alveolar surfaces, remained close to one of the Mauritian
species (C. neraudii) and did not show advanced specializations
as in the other three species. Therefore it could have colonized
Reunion in a relatively recent period from an ancestor related
to that Mauritian species. Its distribution on the island,
restricted as far as we know to the leeward regions (the western
part), reinforces the hypothesis of a recent immigration. It is
not possible to know, however, if it reached the island before or
after the explosive phenomena of the Piton des Neiges, or if
Reunion housed in far-off days a previous population of tortoises
that was exterminated together with other representatives
of the original fauna. We must remember that the first vestiges
of the Bourbon tortoise, their whereabouts unfortunately unknown,
were found by L. Maillard in 1854, at Cap La Houssaye,
under four meters of lava (Bour, 1980b). Were they the
representatives of an ancient population, wiped out a long time
ago by a cataclysm, or were they the ancestors of the recently
extinct form?
As a result of the above considerations, we propose the hypothesis
that most of the birds that were present on Reunion
colonized the island only after the explosive episodes of Piton
des Neiges.
At the time when the Europeans were colonizing the island,
the Reunion avifauna included about 33 species of resident
land birds (Table 13). Of these 33 species, 14 have been found
as fossils. Among those that were certainly present but have
not been found as fossils are members of the genera Circus,
Alectroenas, Psittacula, Collocalia, and all the small passerines,
Phedina, Coracina, Hypsipetes, Terpsiphone, Saxicola,
Zosterops, and Foudia. We think that the small passerines were
not present in the fossiliferous sites that we have exploited.
Among these 33 species, 17 (52%) are extinct, four or five are
no longer present on Reunion, and 11 are still present there.
Among the 11 surviving species, eight are very small birds
(Apodiformes and Passeriformes), and one species, Coracina
newtoni (Pollen), is very endangered.
The extinctions took place very rapidly, over a period of two
centuries from 1646. A first group of species, reported by the
early visitors and by Dubois (1674), in 1671-1672, became extinct
almost immediately because they are not mentioned afterwards.
Species that disappeared at that time are Nycticorax
duboisi, Alopochen {M.) kervazoi, Anas theodori, Falco duboisi,
a smaller falcon known as Emerillon, Dryolimnas augusti,
Fulica newtonii, a parrot known as perroquet vert a
tete...couleur defeu, and Foudia sp. In Dubois' time the island
had only 314 human inhabitants (Bour, 1980a). Rats were absent
in 1671, as indicated in the log of Le Breton and by Dubois
(1674) in 1671-1672, but they invaded the island in 1675
(Cheke, 1987). This first wave of extinction mainly included
aquatic forms that were living in the ponds and marshes of the
west coast, the area that was first settled. There was no other
refuge possible for these species. They were still able to fly but
they had become flightless in their behavior. Numerous writers
emphasize how tame they were and how easily they allowed
themselves to be killed without fleeing. Moreover, anseriforms
are very vulnerable during their period of molt. The two falcons
were perhaps adapted for capturing prey living in the dry
west coast palm savanna and the western lowland dry forest,
environments that were completely cleared for cultivation. According
to Cheke (1987), Foudia was exterminated by rats.
The second wave included species mentioned by Feuilley in
1704 (Barre and Barau, 1982) but not recorded thereafter. Species
that disappeared at that time are a cormorant (probably
Phalacrocorax africanus (Gmelin)), an egret (probably Egretta
dimorpha Hartert), Phoenicopterus ruber, Threskiornis solitarius,
and four species of pigeons, Alectroenas sp., Nesoenas
duboisi, Streptopelia picturata, and another dove. Flamingos
were known to be breeding on the island, and they are vulnerable
during their colonial nesting. The Reunion Ibis, known as
"Solitaire," survived for a short time, taking refuge in the
mountains, but it was decreasing and was not reported after
1708. Cats were introduced into the island in 1703 to fight rats
and must have played a large part in the destmction of birds because
in 1704 Feuilley wrote: "Ramiers have not been seen for
some time, either they have deserted the island, or they have
been destroyed by the cats," and, concerning the huppes
{Fregilupus) and the merles {Hypsipetes): "Marron cats destroy
many of them. These birds let the cats get very close and
they are caught without getting out of their places" (Barre and
Barau, 1982:38, our translation).
Then, between 1734 and 1740, Oiseau bleu, a grey parrot,
and a parakeet, Psittacula eques/echo, disappeared, followed
about 1780 by Mascarinus mascarinus, and lastly, between
1838 and 1858, by Fregilupus varius. According to Cheke
(1987:24) the Solitaire and Oiseau bleu "were probably victims
of feral cats but the parrots may have been dependent on the
lowland habitats."
It is difficult to evaluate accurately the role played by different
factors in the extinction of these birds. But these factors—
excessive hunting by humans, the action of introduced predators
(e.g, pigs, rats, cats), and habitat destmction—cannot account
for the disappearance of the Reunion Starling, for which
the introduction of a disease or parasite has been invoked
(Cheke, 1987).
The example of Reunion shows that, in an insular environment,
flying birds disappear almost as quickly as flightless
ones. The relief of Reunion is very mgged, much more than
that of Mauritius or Rodrigues. It has many places that are difficult
to reach and where birds may have been protected, but
this mgged topography did not prevent the tame, naive birds of
Reunion from disappearing.