Column headings:
A: No.
B: Wing
C: Longest tail feather
D: Shortest tail feather
E: Exposed culmen
F: Depth Culmen
G: Tarsus
======================+====+=======+=======+=====+=====+=======+=========
LOCATION | A | B | C | D | E | F | G
----------------------+----+-------+-------+-----+-----+-------+---------
_Gygis alba candida_ | | | | | | |
(Gmelin) | | | | | | |
| | | | | | |
Japan, Bonins | 4 | 238 | 109 | 65 | 36 | |
| | | | |34-38| |
| | | | | | |
Mariana Islands | 35 | 237 | 111 | 69 | 38 | 9.0 | 13.0
| |227-246| 98-120|61-75|36-41| |12.0-14.0
| | | | | | |
Wake Islands | 10 | 236 | 109 | 69 | 38 | | 13.0
| |232-243|101-118|64-77|37-41| |13.0-14.0
| | | | | | |
Hawaiian Islands | 36 | 235 | 109 | 68 | 37 | 8.5 | 13.0
| |220-246|102-118|64-74|33-40|8.0-9.0|12.0-14.0
| | | | | | |
Marshall Islands | 4 | 234 | 111 | 71 | 39 | |
| |231-238|107-115|70-73|38-40| |
| | | | | | |
Phoenix, Howland, | | | | | | |
Hull, Canton Islds.| 8 | 238 | 107 | 70 | 39 | 8.5 | 14.0
| |237-240|101-116|64-76|37-41| |
| | | | | | |
Fanning, Washington,| | | | | | |
Christmas Islands | 19 | 238 | 107 | 68 | 38 | 8.0 | 13.5
| |227-242| 97-119|65-72|37-42|7.5-9.0|12.0-15.0
+----+-------+-------+-----+-----+-------+---------
Totals |116 | 236 | 109 | 69 | 38 | 8.5 | 13.0
| |220-246|107-120|61-77|33-42|7.5-9.0|12.0-15.0
| +=======+=======+=====+=====+=======+=========
_Gygis alba pacifica_ | | | | | | |
(Lesson) | | | | | | |
| | | | | | |
Caroline, Palau | | | | | | |
Islands | 33 | 245 | 116 | 73 | 42 | 8.5 | 13.5
| |236-253|112-125|67-76|38-44| |13.0-13.5
| | | | | | |
Bismarck Arch., | | | | | | |
Solomon Islands | 12 | 247 | 116 | 74 | 42 | |
| |242-256|105-129|68-78|39-45| |
| | | | | | |
Samoa, Wallis, Fiji,| | | | | | |
Tonga, Niue Islands| 20 | 247 | 115 | 71 | 42 | |
| |239-254|110-127|67-78|39-44| |
| | | | | | |
Line, Danger Islands| 13 | 245 | 115 | 73 | 41 | |
| |238-252|107-118|69-78|39-42| |
| | | | | | |
Cook,Austral Islands| 29 | 247 | 114 | 73 | 42 | |
| |241-255|104-124|65-78|40-45| |
| | | | | | |
Society Islands | 37 | 249 | 113 | 71 | 42 | 8.5 | 13.5
| |241-257|107-126|62-76|40-45|8.0-9.0|12.0-14.0
| | | | | | |
Tuamotu Arch |118 | 245 | 114 | 72 | 42 | |
| |236-252|107-127|62-82|38-46| |
| | | | | | |
Rapa, Bass Rocks, | | | | | | |
Oeno, Henderson, | | | | | | |
Ducie, Pitcairn, | | | | | | |
Easter Islands | 54 | 247 | 113 | 73 | 41 | |
| |240-255|106-126|63-84|40-45| |
| | | | | | |
Clipperton, Cocos | | | | | | |
Islands | 10 | 245 | 115 | 72 | 40 | 8.5 | 13.5
| |240-253|110-120|71-73|38-43|8.5-9.5|13.0-14.0
+----+-------+-------+-----+-----+-------+---------
Totals |326 | 246 | 114 | 72 | 42 | 8.5 | 13.5
| |236-257|104-129|62-84|38-46|8.0-9.5|12.0-14.0
| +=======+=======+=====+=====+=======+=========
Intergrades between | | | | | | |
_G. a. microrhyncha_| | | | | | |
and _G. a. pacifica_| 9 | 237 | 105 | 74 | 38 | 7.5 | 13.0
| |230-247| 93-122|67-89|36-41|7.0-8.0|12.0-14.0
| | | | | | |
_Gygis alba | | | | | | |
microrhyncha_ | 55 | 218 | 78 | 64 | 36 | 6.5 | 12.0
| |211-235| 72-96 |60-75|32-39|6.0-8.0|11.0-12.5
| | | | | | |
_Gygis alba royana_ | | | | | | |
Mathews | | | | | | |
| | | | | | |
Norfolk Islands | 16 | 250 | 113 | 73 | 42 | |
| |242-257|105-124|68-79|41-44| |
| | | | | | |
Kermadec Islands | 12 | 251 | 115 | 75 | 43 | |
| |244-255|110-121|71-81|40-46| |
+----+-------+-------+-----+-----+-------+---------
Totals | 28 | 250 | 114 | 74 | 42 | |
| |242-257|105-124|68-81|40-46| |
----------------------+----+-------+-------+-----+-----+-------+---------
The measurements indicate that there is a gradient in size from small in
the north to large in the south; however, there is a definite separation
in average measurements--ten millimeters in length of wing and four
millimeters in length of exposed culmen--between the two populations
which are designated as _G. a. candida_ and _G. a. pacifica_. In
studying material from Micronesia and the Hawaiian Islands, I (1948:57)
pointed out the similarities between birds of the Marianas and the
Hawaiians and separated these from terns found in the Caroline Islands.
The systematic position of the White Tern in the Gilbert and Ellice
islands will remain in doubt until specimens are available for
examination.
_G. a. royana_ is provisionally retained as the name for the Fairy Tern
of the Kermadecs and Norfolk Island; there is considerable overlap in
measurements between _G. a. royana_ and _G. a. pacifica_. Measurements
have given evidence of the degrees of structural resemblance of the
White Terns of the different islands, but it is not certain that the
groupings made on this basis are natural; more data is needed on ecology
and life history. Of particular importance is to learn whether these
birds fly regularly from island to island. On the basis of eleven months
of rather continuous observation in Micronesia, I suspect that the White
Tern has little tendency to make inter-island migrations. This might
account for the differences in size in the populations at Guam in the
Marianas (_G. a. candida_) and at Ulithi in the Carolines (_G. a.
pacifica_) where only approximately 400 miles of open water separate the
two islands. The occurrence of the distinct _G. a. microrhyncha_ in the
Marquesas may be accounted for by such nonmigratory behavior. Mayr
(1945a:27), however, is of the opinion that White Terns found in the
Bismarck Archipelago, the Solomons, Santa Cruz and New Hebrides islands
may not breed there, which is another way of saying that they are
migrants. Swarth (1934:221) and Murphy (1936:1268) record the wandering
of the White Tern to the Galapagos Islands, probably from breeding
grounds at Cocos Island. Swarth suggests that the tern is not
established at the Galapagos because of the presence of colder water in
the area. Murphy (1936:1166) is of the opinion that the South Atlantic
White Terns are sedentary, but reports evidence of pelagic migration in
the Pacific at the Kermadecs. The fact that _G. alba_ is restricted in
its distribution to widely separated groups of islands in tropical and
subtropical areas of the South Atlantic, Indian and Pacific oceans may
indicate that the birds at one time had a more extensive range than at
present, probably including even coastal regions of the continents and
large continental islands.
=Gygis alba pacifica= (Lesson)