TABLE 3. BREEDING AND WINTERING GROUNDS OF THE SPECIES OF MIGRATORY
SHORE BIRDS IN MICRONESIA
PART A. Location of breeding grounds
==================+========+================+=========+==========
CLASS | Number | Circumpolar[A] | Asiatic | American
------------------+--------+----------------+---------+----------
Regular visitors | 17 | 5 | 10 | 2
Uncommon visitors | 11 | 2 | 8 | 1
+--------+----------------+---------+----------
Totals | 28 | 7 | 18 | 3
------------------+--------+----------------+---------+----------
PART B. Location of wintering grounds
------------------+--------+---------+---------+----------+---------
CLASS | Number | Circum- | Asiatic | American | Oceanic
|tropical| | | |
------------------+--------+---------+---------+----------+---------
Regular visitors | 17 | 2 | 13 | 1 | 1
Uncommon visitors | 11 | 1 | 8 | 2 | 0
+--------+---------+---------+----------+---------
Totals | 28 | 3 | 21 | 3 | 1
------------------+--------+---------+---------+----------+---------
[A] Denotes birds which breed on both American and Asiatic sides of the
Pacific Ocean.
The shore birds which are known to visit Micronesia breed in the
Northern Hemisphere. Table 3 summarizes the data concerning the
breeding and wintering areas of these birds. As shown in part A of table
3, 18 of the 28 species which visit Micronesia come from Asiatic
breeding grounds. Seven have circumpolar breeding ranges and three (two
are regular visitors) come from American breeding grounds. As shown in
part B of table 3, 21 of the 28 waders have their winter ranges on the
Asiatic side of the Pacific with eastern extensions to Micronesia and
other parts of Oceania. Of the 7 remaining species, the winter ranges of
three are circumtropical; the winter range of a fourth is restricted to
Oceania; and the winter ranges of the remaining three (two classed as
uncommon visitors) are American.
Bryan and Greenway (1944:109-115) record 14 species of shore birds from
the Hawaiian Islands. One of these, _Himantopus himantopus knudsoni_, is
a resident, probably of New World origin, according to Mayr (1943:56).
The others, listed in table 7, include three species unknown in
Micronesia. One of these, _Phalaropus fulicarus_, apparently winters at
sea off the west coast of South America. The other two species
(_Charadrius vociferus vociferus_ and _Gallinago delicata_) are
classified by Bryan and Greenway as "accidental" and "occasional"
visitors from North America. The ten species common to both the Hawaiian
Islands and Micronesia include seven whose breeding grounds are
circumpolar, two whose breeding grounds are in Arctic America and one
whose breeding ground is in Arctic Asia. The winter ranges of these ten
species include four which are circumtropical, three which are Asiatic,
one which is restricted to Oceania, and only two which are American.
The ability of the shore birds to migrate almost as well over water as
over land may explain their spread into Oceania. The likelihood that
shore birds, when migrating may have ventured to Micronesia and
Polynesia initially from the Asiatic side of the Pacific is strongly
suggested by the data given in the paragraph above. Also, on the Asiatic
side of the Pacific there are large numbers of islands, which form
several archipelagoes extending from Kamchatka south to Malaysia. Once
accustomed to migrating along these chains of islands from the Arctic to
Australia, birds would probably have to make only minor adjustments to
extend the breadth of their migratory routes eastward into the islands
of the Pacific Ocean. In contrast, on the Pacific coast of North America
there are few coastal or offshore islands and there is a vast area of
open water separating the Hawaiian Islands from the American mainland.
Probably the vastness of this area of water offers little stimulus to
birds to expand their migratory ranges westward, and in part accounts
for the small North American contingent in the population of shore birds
of the Central Pacific. Some North American shore birds do visit the
Pacific. The brisk trade winds from the northeast might be an aid to the
birds in their flights from Nearctica to Hawaii.
The long flight now made by shore birds going from the Aleutians to the
Hawaiian Islands may have commenced as a gradual expansion from the
west, or perhaps such a route was initiated by birds flying northward
through the Hawaiian Chain to the Arctic in migrating to their breeding
grounds, and then later returning _via_ the same route to reach their
wintering grounds.