[Illustration: FIG. 8. Faunal areas from which the resident land birds
and fresh-water birds of Micronesia have been derived. (1) Palearctica;
(2) Philippines; (3) Moluccas and Celebes (Malaysia); (4) Melanesia (New
Guinea and northern Melanesia); (5) Polynesia.]
Birds of Micronesia which have been derived directly from Palearctica
are _Gallinula chloropus guami_, _Otus podarginus_, _Asio flammeus_,
_Acrocephalus luscinia_ and _Anas oustaleti_. Apparently _Gallinula_,
_Asio_, and _Acrocephalus_ arrived in Micronesia by way of the chain of
islands from Japan southward to the Bonins, Volcanoes, and Marianas.
_Otus_ reached Palau from Asia, possibly by way of the Philippines. The
smallness of the representation of this component may result partly from
lesser ability of the northern birds to adapt themselves to, and to
establish themselves on, the semi-tropical and tropical islands of
Micronesia as compared with birds from Melanesia where the climate and
ecologic conditions resemble more closely those found in Micronesia.
Evidence supporting this possibility is the large number of Palearctic
residents in the Bonin and Volcano islands as compared with fewer in the
Marianas; the Bonins and Volcanoes are less tropical and more temperate
in climate.
Table 11 lists the birds concerned, by faunal areas from which the birds
have been derived and shows the number of kinds of birds which are
present as a result of these colonizations. There is some overlap in the
numbers since some endemics may be found in more than one area in
Micronesia. Figure 8 shows the faunal areas from which the endemic land
and fresh-water birds of Micronesia have been derived. Melanesia (Papua)
supplied 52 percent of this population. Birds reaching Micronesia by way
of the Moluccas and Celebes include 21 percent of the total population.
The Philippines have supplied 10 percent; Polynesia, 9 percent; and
Palearctica, 8 percent. This population of endemic land birds and
fresh-water birds has seemingly evolved from 46 colonizations, of which
27 have been derived from Melanesia, 6 from the Philippines, 5 from the
Moluccan and Celebean areas, 5 from Palearctica, and 3 from Polynesia.
The Palaus have received a large part of their avifauna from the west
(Moluccas, Philippines, Palearctica). Their Melanesian component is
mostly the result of secondary colonization from the Carolines. The
Carolines have received a greater share of their land birds and
fresh-water birds from Melanesia and a smaller share from Polynesia. The
Marshalls are definitely associated with the Polynesian element. The
Marianas exhibit a considerable amount of secondary colonization from
other Micronesian islands, as well as some unique components from the
Philippines, Melanesia, and Palearctica. Thus, the number of endemics in
Micronesia provides little information concerning the actual number of
successful colonizations by birds from other areas. Many of the endemics
probably have resulted in this way: Individuals of an endemic subspecies
flew to another island and there underwent further differentiation,
producing another endemic subspecies. Such secondary colonization
probably is going on now.
This analysis of the avifauna shows that Micronesia, with the exception
of the Marshall Islands (and the Gilbert Islands), has but little
affinity to Polynesia. It has greater affinity, from the zoogeographical
standpoint, with the Papuan Region (Melanesia).
TABLE 11. AVIFAUNAL COMPONENTS WHICH MAKE UP THE ENDEMIC RESIDENT LAND
AND FRESH-WATER BIRD POPULATION OF MICRONESIA
=================+=======+=============+===========+==========+==========
| | Western | | |
FAUNAL COMPONENT | Palau | and central | Eastern | Marianas | Marshalls
| | Carolines | Carolines | |
-----------------+-------+-------------+-----------+----------+----------
Polynesian | 2 | 3 | 5 | 0 | 3
Melanesian | 11 | 14 | 16 | 12 | 0
Moluccan-Celebean| 6 | 3 | 4 | 7 | 0
Philippine | 6 | 2 | 2 | 4 | 1
Palearctic | 2 | 1 | 2 | 5 | 0
+-------+-------------+-----------+----------+----------
Totals | 27 | 23 | 29 | 28 | 4
-----------------+-------+-------------+-----------+----------+----------