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NUMBER 89 71
Mallorca, probably in prehuman levels, and in the late Pleistocene
from Corsica-Sardinia (Alcover et al., 1992). Their
presence is probably related to the presence of small mammals
on these islands {Hypnomys and Nesiotites in the Gymnesic Islands,
Nesiotites, Rhagamys, Microtus, and Prolagus in Corsica-Sardinia),
whereas small mammals are absent from Eivissa.
It is not possible, however, to infer in a strict sense the absence
of Tytonidae on islands without small mammals. For example,
in the Galapagos and Canary islands different small mammals
have been recorded on some of the islands but not on all of
them. In these archipelagos, fytonids have even been obtained
in prehuman deposits on islands without small mammals
(Steadman, 1986; Alcover, unpublished).
Strigid owls that prey on vertebrates are unknown in the fossil
record of Mallorca. Although Otus scops and Athene noctua
do occur in the fossil record, these species feed mainly on insects.
Asio flammeus and Bubo insular is are present in the fossil
record on Sardinia, and Bubo insularis, Asio otus, and a
new, undescribed species of Athene have been found as fossils
on Corsica (Mourer-Chauvire, pers. comm., 1996). Several remains
of Asio flammeus and those of a single individual of a
large species of Strigidae, probably Bubo bubo, have been
found in the late Pleistocene of Eivissa (Alcover et al., 1992;
Sondaar et al., 1995). Asio flammeus, the more abundant strigid
on Eivissa, is more diurnally active than other Palearctic species
of owls of the same size, like Asio otus or Strix aluco
(Cramp, 1985). This behavioral pattern may have been advantageous
for preying on birds, which were the primary food
available on Eivissa before human colonization. Circadian
rhythms might differ between insular and continental systems
(Granjon and Cheylan, 1990, 1993, gave an example of change
of circadian rhythms in a mammalian species). Asio flammeus
may have been more diurnal on Eivissa than in other areas of
its range.
The endemic genus Grallistrix lived in the Hawaiian Islands
(Olson and James, 1991). This genus shows anatomical specializations
for bird-catching (elongated legs and shortened
wings). Its ornithophagous habits have been confirmed by fossil
pellets (Olson and James, 1991). The main activity period of
Grallistrix is unknown, but its ability to catch and kill birds in
flight suggests that the species of this genus may have been
more diurnal than other Strigidae.
Hawks and falcons are widely distributed on western Mediterranean
islands and have been found as fossils on all those islands
studied herein. In the Hawaiian Islands this BTT is occupied
by Circus dossenus, a species convergent with bird-eating
hawks of the genus Accipiter (Olson and James, 1991). On
Mediterranean islands with mammals, species of Buteo (with a
diet of small mammals and small- and medium-sized reptiles),
species of Circus and Milvus (each with a varied diet), and
small species of the genus Falco (mainly herpetophagous and
entomophagous) have been found (Alcover et al., 1992). This
BTT is occupied by Buteo solitarius in the Hawaiian Islands
(Olson and James, 1991), whereas in Eivissa it is represented
by Circus cyaneus, which is scarce in the fossil record, and by
small species of the more abundant Falco (Sondaar et al.,
1995).
Pelagic sea birds are not found on the large western Mediterranean
islands with mammals, being unknown in Corsica and
Sardinia (Alcover et al., 1992). On the other hand, the small island
of Tavolara, near Sardinia, has yielded fossil remains of
Calonectris diomedea and Puffinus yelkouan (Mayaud and
Schaub, 1950). Significantly, Procellariiformes were abundant
in the Pityusic Islands. Many fossil bones of Puffinus mauretanicus
and scarcer remains of Calonectris diomedea and Hydrobates
pelagicus have been found in Eivissa (Sondaar et al.,
1995). Similarly, abundant remains of procellariforms, such as
the extinct, small-sized gadfly petrel Pterodroma jugabilis (Olson
and James, 1991), have been found in Oahu and Hawaii,
and many other Procellariidae are commonly encountered.
The BTT that includes the nonpasseriform species with a
wide diet (malacophagous, insectivorous, detritivorous, and
herbivorous birds) has a better representation on the Pityusic
and Hawaiian islands than on the other western Mediterranean
islands. Two or more flightless species of ibis belonging to the
extinct genus Apteribis lived on the Hawaiian islands Molokai,
Maui, and Lanai, which constituted the Pleistocene island of
Maui Nui (Olson and James, 1991). The genera Otis (bustards)
and Grus (cranes) can be considered to be the Palearctic ecological
analogs of these species. Both are common in the Eivissan
fossil record but are not as common on the other western
Mediterranean islands: so far, only a few remains of one specimen
of Grus have been obtained in Mallorca (Mourer-Chauvire
et al., 1975), and a few remains of Otis have been found on
Corsica (Mourer-Chauvire, pers. comm., 1996).
Among the rails, only a few remains of Porzana have been
recorded on Mallorca, and no rails have been found in the Sardinian
fossil record. Four species of rails are infrequently encountered
in the fossil record of Corsica (Alcover et al., 1992),
whereas rails are well represented in the late Pleistocene of
Eivissa as well as on the Hawaiian Islands. Endemic species
have evolved on the Hawaiian Islands and on Evissa but not on
the other western Mediterranean islands. An endemic undescribed
form of Rallus lived on Eivissa (McMinn, in prep.),
whereas the genus Porzana underwent a significant radiation in
the Hawaiian Islands (Olson and James, 1991).
The BTTs occupied by Passeriformes are not as easily defined
as those occupied by nonpasserines. Thus, only three
BTTs were considered for the Passeriformes. Some patterns,
coming mainly from corvids, emerged from our analysis. On
all the islands studied, corvids played an important role. Pyrrhocorax
was present during the late Pleistocene on all the
western Mediterranean islands. At least one small-sized species
of Corvus also was present in Corsica, Sardinia, and Mallorca.
Large-sized species of Corvus are scarce in the fossil record of
Mallorca, Corsica, and Sardinia. In contrast, on Eivissa abundant
remains of a large Corvus, initially identified as C. antecorax
(Florit et al., 1986), but whose identity is now under revision
(McMinn, in prep.), have been recorded. In the
Pleistocene of the Hawaiian Islands three large-sized species of