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Corvus have been found: the extinct C. impluviatus James and
Olson (1991) and C viriosus James and Olson (1991) and the
extant C. hawaiiensis. Probably all the large Hawaiian and
Mediterranean species of Corvus represent roughly the same
BTT. The scarcity of large crows on the Mediterranean islands
with terrestrial mammals, in contrast with their abundance in
Eivissa and the Hawaiian Islands, reinforces the parallels between
the two archipelagos.
The BTT that includes small-sized corvids on the Mediterranean
islands is tentatively paralleled by the Hawaiian genus
Aidemedia, which on the basis of its jaws was thought to have
dietary habits similar to those of Sturnus (James and Olson,
1991). Sturnus is present in the fossil records of Mallorca (Segui
et al., 1997), Corsica, and Sardinia (Alcover et al., 1992), although
it is considerably scarcer than Pyrrhocorax. The living
representatives of both genera have opportunistic dietary habits
and eat lots of fleshy fruits.
The small Passeriformes (perching birds) are included in a
very wide range of BTTs that are more difficult to characterize
than the larger species, compounded by the fact that they often
change their BTT through the year. Because of these and other
considerations we have omitted them from Table 3, except for
small granivorous species, which are included to show that the
members of a variety of families occupy the same BTT on the
Mediterranean islands as do some granivorous species of
Drepanidini in the Hawaiian Islands. A similar pattern among
granivorous passerines in the Galapagos Islands (all belonging
to a single radiation) and in the Canary Islands (where species
belonging to different families occupy this BTT) has been recorded.
Discussion
The peculiarity of the Eivissan paleoavifauna within the
Mediterranean region is clearly supported by the preceding
analysis. The late Pleistocene fauna of Eivissa was structured
along similar lines to that of the Hawaiian Islands: Anseriformes
as the most important middle-sized grazers, sea-eagles
as superpredators, mammal-eating tytonids absent, bird-catching
strigids with more diurnal behaviour present, diurnal birds
of prey (bird-catching specialists or more generalists) present,
ground-dwelling species with varying food habits (i.e., medium-
and small-sized malacophagous, insectivorous, detritivorous,
and herbivorous species), along with flying, omnivorous,
medium-sized passerines (large corvids). In the faunas of the
other Mediterranean islands, where land mammals were
present, the paleornithological communities were structured in
very different ways.
One of the main points to be emphasized is that the greatest
parallel to the late Pleistocene bird community of Eivissa is not
on the other Mediterranean islands, the Atlantic or Indian oceanic
islands that lack terrestrial mammals, or on the majority of
Pacific islands, but on the very distant and isolated Hawaiian
Islands. Conversely, the most accurate parallel to the Hawaiian
SMITHSONIAN CONTRIBUTIONS TO PALEOBIOLOGY
paleoavifauna, according to the assignment of the different
BTTs, is not to found among the other Pacific Islands, or
among the Atlantic Islands, but rather in the late Pleistocene
fauna from Eivissa. The significance of such an ecological relationship
is currently unknown. Nevertheless, there is no doubt
that an accurate study of the Eivissan fossil avifauna will be
useful for the understanding of the development of the Hawaiian
avifauna, and vice versa. In any case, the striking similarity
between the avian paleocommunities of the Hawaiian Islands
and the Pityusic Islands reinforces criticisms of the randomness
of the ecological processes of immigration and extinction in the
development of insular communities.
One point of interest of the present analysis is its predictive
character. We have an accurate knowledge of the late Pleistocene
fauna from Eivissa, contrasting with scarce data on late
Pliocene/early Pleistocene bird fauna of the island (Alcover,
1989, and unpublished data). During this earlier period, a vertebrate
fauna, including a giant tortoise and at least two terrestrial
mammals, lived on Eivissa. In addition, a varied mollusk fauna
of at least 22 species also was present. These faunas suffered a
dramatic, early or middle Pleistocene extinction event (Alcover
et al., 1994). The avifauna associated with the giant tortoise episode
is as yet poorly known, although it likely was substantially
different from the late Pleistocene avifauna. The mass extinction
on Eivissa must have forced a change in the
composition and structure of the bird communities.
Study of the fossil bird fauna from Menorca also should be
enlightening. This island, which is about same size as Eivissa,
was occupied by Myotragus balearicus Bate, a terrestrial ungulate
that must be considered a key species in the ecosystem. If
the size of the island alone was the key factor in determining its
fauna, the late Pleistocene fossil avifauna from Menorca would
have been similar to that of Eivissa. But if the island's ecology
has greater importance in determining its fauna, as we postulate,
the late Pleistocene avifauna from Menorca will cluster
with that of Mallorca, where Myotragus also was present.
CATALAN SUMMARY
La comparacio entre les avifaunes pleistoceniques de les illes de
la Mediterrania occidental (Gimnesies, Pitiuses, Massis cirnosard)
documenta l'existencia de dues castes de comunitats ornitiques
en el passat: una a les illes habitades per mamifers terrestres
(Gimnesies, Corsega, i Sardenya) i raltra a les illes que no en contenen
(Pitiuses). Les comunitats ornitiques pitiuses troben el seu
paral.lelisme mes evident a les comunitats ornitiques prehumanes
de les Hawaii, mentre que les comunitats ornitiques de les altres
illes de la Mediterrania Occidental s'addiuen mes amb les de les
illes de la Mediterrania Oriental. El factor clau per entendre
I'estructuracio de les comunitats ornitiques insulars mediterxanies
del Pleistoce sembla esser la presencia/absencia de mamifers herbivors
de talla mitjana {Myotragus balearicus Bate a les Gimnesies
i Megaceros caziotti (Deperet) al massis cimo-sard).