| Location | No. | Wing | Longest tail feather | Shortest tail feather | Exposed culmen | Tarsus |
| Thalasseus bergii pelecanoides Palaus, Carolines, Marshalls | 6 | 343 | 168 | 82 | 60 | |
| 334-352 | 153-184 | 80-85 | 58-65 | |||
| Christmas, Phoenix, Tuamotus, Society, Fiji, Loyalty, New Hebrides | 48 | 344 | 170 | 83 | 58 | 27 |
| 329-362 | 145-198 | 77-92 | 54-64 | 25-29 | ||
| Eastern Australia | 14 | 345 | 165 | 88 | 58 | 27 |
| 338-349 | 152-174 | 84-92 | 55-63 | 26-29 | ||
| New Guinea, Bismarck, Archipelago, Moluccas | 18 | 342 | 168 | 81 | 59 | 27 |
| 332-361 | 144-194 | 75-87 | 53-64 | 26-28 | ||
| Totals | 86 | 344 | 169 | 83 | 58 | 27 |
| 329-362 | 144-198 | 75-92 | 53-65 | 25-29 | ||
| Thalasseus bergii cristatus Philippines, China, Formosa, Riu Kius | 18 | 332 | 162 | 81 | 58 | 28 |
| 324-342 | 149-182 | 78-87 | 55-64 | 26-30 | ||
| Thalasseus bergii gwendolenae Western Australia | 14 | 354 | 171 | 86 | 58 | 27 |
| 339-369 | 162-182 | 81-91 | 53-65 | 25-29 |
Table 21. Measurements of Anoüs stolidus of the Pacific Area
Table 21. Measurements of Anoüs stolidus of the Pacific Area
Geographic range.—Islands in the Indian Ocean east to tropical parts of western and central Pacific. In Micronesia: Mariana Islands—Agrihan, Asuncion, Saipan, Rota, Guam; Palau Islands—Kayangel, Babelthuap, Koror, Urukthapel, Ngabad, Peleliu, Angaur; Caroline Islands—Ulithi, Truk, Wolea, Mortlock, Lukunor, Nukuoro, Ponapé, Kusaie; Marshall Islands—Jaluit, Mille, Aurh, Wotze, Bikini, Kwajalein.
Characters.—Adult: A large, dark-brown tern with grayish crown and whitish forehead; line above eye white; crescent of white on lower eyelid; lores blackish; bill black; feet brownish, iris dark.
Immature: Resembles adult, but lighter and browner and top of head grayish-brown.
A. s. pileatus resembles A. s. ridgwayi, but darker and less brownish, although not so dark as A. s. galapagensis; forehead and crown usually duller; length of wing and tail average larger (282 and 161) than in A. s. ridgwayi (278 and 158) and A. s. galapagensis (277 and 151).
Measurements.—Measurements of the Common Noddy of the Pacific area are listed in [table 21].
Weights.—In 1948 (1948:56) I listed the weights of specimens from Guam and Rota as follows: four adult males 187-204 (197); three adult females 177-203 (189).
Specimens examined.—Total number, 92 (43 males, 39 females, 10 unsexed), as follows: Mariana Islands, USNM—Guam, 7 (May 24, June 15, July 6, 21)—Rota, 3 (Oct. 18, 24); AMNH—Guam, 4 (April 21, 27, Aug. 18)—Asuncion, 1 (Jan. 18); Palau Islands, USNM—Peleliu, 2 (Sept. 1)—Ngabad, 1 (Sept. 11); AMNH—exact locality not given, 6 (Nov. 3, 8); Caroline Islands, USNM—Ulithi, 3 (Aug. 15)—Kusaie, 1 (Feb. 8); AMNH—Truk, 15 (Feb. 1, 8, 25, March 10, May 6, June 12, 13, Nov. 25, Dec. 25)—Ponapé, 20 (Dec. 3, 5, 8, 12, 15)—Kusaie, 24 (Jan., March 10-30, April 1-10); Marshall Islands, USNM—Bikini, 5 (Feb. 28, March 2, 19).
Nesting.—Murphy (1936:1152) writes that the Atlantic subspecies, A. s. stolidus, breeds in tropical localities every month of the year, although there may be a part of the resident population away at sea at any given time. In the Pacific area, Kirby (1925:187) found nests "on platforms of sticks built on tufts of grass" at Christmas Island in August. In Micronesia, Coultas obtained young birds at Kusaie in January and April and commented (field notes) that they probably nest "spasmodically at all times of the year." At Ponapé, Coultas observed nests in high trees in December, and birds obtained by him in that month had enlarged gonads. At Bikini, Morrison obtained eggs on March 2 and 19, and young on March 19. At Palau, Coultas took one female tern in postnatal molt on November 8. Adults obtained by him in that month had enlarged gonads. At Ulithi, the NAMRU2 party recorded one nest containing a single egg on August 21. At the same atoll the NAMRU2 party received reports of a large colony of nesting noddys in May to July, 1945. In the following August few noddies were seen by the NAMRU2 party. McElroy found nests on cliffs and in coconut trees at Truk in December, 1945. Hartert (1900:10) reports on eggs taken at Truk in the period from March to July 1. The NAMRU2 party observed birds carrying nest materials at Peleliu on August 28 but failed to find the nests. At Guam, the writer found terns in numbers varying from 4 to 75 in May to July, 1945, along the rocky cliffs but no evidence of nesting activity was obtained. Strophlet (1946:537) reports that nests may have been present on Orote Peninsula at Guam on December 13, 1945. Coultas (field notes) is of the opinion that the birds do not nest at Guam but do nest farther north in the Marianas. Borror (1947:417) found two colonies at Agrihan on August 10, 1945. Thus, there are records of nesting in nine months of the year in Micronesia; although I suspect that the larger flocks of terns have more regular breeding habits correlated with their pelagic feeding activities. "Stragglers" probably nest irregularly.
Food habits.—The author (1948:56) records small fish and crustaceans in stomachs of terns taken at Ulithi and Peleliu. At Ypao Point, Guam, birds were seen to fly back and forth in the day from their roosts on the sea-cliffs. On one occasion I saw these birds feeding approximately a half mile from shore.
Parasites.—Wharton (1946:174) and Wharton and Hardcastle (1946:292, 296, 306) list the following species of chiggers (Acarina) from the Common Noddy from Guam and Ulithi: Neoschöngastia bougainvillensis, N. americana solomonis, N. egretta, Acariscus pluvius, and A. anous. Uchida (1918:484, 488) found the bird louse (Mallophaga), Nirmus separatus, on terms at Palau and at Ponapé he found Colpocephalum milleri on the bird. Bequaert (in litt.) has identified a fly (Hippoboscidae) as Olfersia aenescens from a tern from Rota.
Remarks.—Of the Common Noddy Tern of the Pacific area, three subspecies are recognized by Peters (1934:346-347). Anoüs stolidus ridgwayi is known from islands off the western coast of Mexico and Central America; A. s. galapagensis is recorded from the Galapagos Archipelago; and A. s. pileatus is found on tropical islands throughout the Pacific and west to Madagascar and the African coast in the Indian Ocean. These subspecies differ from one another principally in color, as noted by Ridgway (1919:545); A. s. galapagensis is the darkest form, A. s. ridgwayi is less blackish and more brownish in color of body, and A. s. pileatus is between the two in coloring. A. s. pileatus averages larger in length of wing and tail, but these measurements do not appear to be significant from a taxonomic standpoint.
As shown in [table 21], measurements of length of wing for specimens from throughout most of the Pacific area are almost the same. Length of tail is correspondingly uniform. There is a gradual increase in size of birds in the Tuamotus and Societies and east to Easter Island. In this region the average measurement for length of wing is 293 millimeters. The lengths of wing and tails are shorter in specimens from the Kermadecs and Norfolk Island, which may indicate relationships with the smaller birds of the Australian area, Western Melanesia and possibly Malaysia and the Riu Kiu Islands. I am unable to determine the subspecific status of the birds from the Kermadecs and Norfolk Island, because of the lack of sufficient material from the Australian region and Malaysia. Possibly Mathews' name, A. s. gilberti, is valid for the noddys of Australia and also for the birds at Norfolk and the Kermadecs. The small-sized birds of the Riu Kiu Islands have been designated as A. s. pullus by Bangs. When specimens from the type locality of A. s. pileatus in the Philippine Islands are available, the true relationships of the populations from Micronesia and the other areas in the Pacific can be ascertained.
The tern found in the Hawaiians has the palest body and the most chalky-white forehead of any of the birds of the Pacific. Bryan (1903:101) found terns from Marcus Island to agree with specimens from Guam and to be "slightly darker" than birds from Midway and Laysan in the Hawaiian chain. The birds from the Riu Kius are darker and thus similar to the few specimens seen from Malaysia. Birds from Polynesia and Melanesia possess the most sooty underparts while those from Micronesia are only slightly less pale. This condition also seems to be true for the birds in the Australian area and for specimens seen from islands in the Indian Ocean. With fading, or wear, or both, there is a change from dusky black to dusky brown in the plumage; effort was made by me to compare specimens with relatively similar conditions of plumage. In summary, the systematic position of the Common Noddy Terns of the Pacific seemingly depends on the characteristics of specimens from the type locality in the Philippines. When topotypes are available for study, they may be found to be nearer the darker forms of Malaysia or may tend toward the paler, oceanic forms. The Hawaiian population probably is distinct.
In Micronesia the Common Noddy Tern is not a conspicuous bird except during its breeding period. Probably it spends most of its life at sea, being unlike Gygis alba in this respect. Large flocks seem less wary of man than are small groups and singles, which are often easily disturbed. Birds of this species appear to prefer the low atolls and offshore islets where both tall vegetation and bare ground are utilized for nesting or roosting. At Ponapé, Coultas (field notes) observed the birds to fly to sea at daybreak and to begin to return to their roosts by 4:00 pm. Wallace (field notes) observed similar activities at Kwajalein in May, 1944, where he saw approximately forty individuals in a flock with Gygis alba.
Anoüs stolidus is divided naturally into an Atlantic subspecies, which is distinguished by its browner color, and into several subspecies which are distinguished by their blacker color in the Pacific and Indian oceans. Whether the genus and species evolved in the Atlantic or in the Pacific region is not known. If it were the Pacific region, the center of differentiation may very well have been the islands of Oceania. There, relatively little variation is observable within populations covering a large area. To the eastward, birds along the American coast are darker or lighter, to the northward, the birds of Hawaii are paler, to the southward and southwestward, the birds are smaller and to the westward, the birds are smaller and darker. The virtual absence of ground-living, predatory animals which might prey on nesting colonies has probably been a reason for the lack of discrimination by this tern in selecting breeding sites. This is probably true of other birds which nest in colonies.
Anous tenuirostris marcusi (Bryan)
White-capped Noddy
Micranous marcusi Bryan, Occ. Papers Bernice P. Bishop Mus., 2, 1903, p. 101. (Type locality, Marcus Island.)
Sterna tenuirostris Kittlitz, Obser. Zool., in Lutké, Voy. "Le Séniavine," 3, 1836, pp. 286, 308 (Ualan, Ouleai); idem, Denkw. Reise russ. Amer. Micron. und Kamchat., 2, 1858, p. 64 (Ualan).
Anous tenuirostris Hartlaub and Finsch, Proc. Zool. Soc. London, 1872, pp. 90, 113 (Pelew, Carolines); Finsch, Journ. Mus. Godeffroy, 8, 1875, pp. 6, 42 (Palau); Schmeltz and Krause, Ethnogr. Abth. Mus. Godeffroy, 1881, pp. 299, 330 (Mortlock, Nukuor); Stott, Auk, 64, 1947, p. 526 (Saipan).
Anous melanogenys Finsch, Proc. Zool. Soc. London, 1877 (1878), p. 781 (Palau); idem, Journ. f. Ornith., 1880, pp. 295, 308 (Ponapé, Kuschai); idem, Ibis, 1880, pp. 219, 220, 332 (Taluit, Arno); idem, Proc. Zool. Soc. London, 1880, p. 577 (Ruk); idem, Ibis, 1881, pp. 107, 109, 115 (Kuschai, Ponape); Salvadori, Ornith. Papuasia, 3, 1882, p. 456 (Pelew, Ponapé, Marshalls); Finsch, Mitth. Ornith. Ver. Wien, 1884, p. 52 (Jaluit, Arno, Kuschai); Wiglesworth, Abhandl. und Ber. Zool. Mus. Dresden, no. 6, 1890-1901 (1891), p. 77 (Pelew, Ualan, Ponapé, Nukuor, Luganor, Ruk); Hartert, Katalog Vogelsamml. Senckenb., 1891, p. 238 (Ualan); Takatsukasa and Kuroda, Tori, 1, 1915, p. 62 (Ruk); Kuroda, in Momiyama, Birds Micronesia, 1922, p. 50 (Pelew, Ruk, Wolea, Luganor, Nukuor, Ponapé, Kusaie, Marshalls).
Anous leucocapillus Finsch, Proc. Zool. Soc. London, 1877 (1878), p. 781 (Ponapé); Nehrkorn, Journ. f. Ornith., 1879, p. 410 (Ponapé); Schmeltz and Krause, Ethnogr. Abth. Mus. Godeffroy, 1881, p. 281 (Ponapé); Finsch, Mitth. Ornith. Ver. Wien, 1884, p. 52 (Jaluit); Tristram, Cat. Coll. Birds, 1889, p. 10 (Pelew); Salvadori, Ornith. Papuasia, 3, 1882, p. 457 (Pelew); Wiglesworth, Abhandl. und Ber Zool. Mus. Dresden, no. 6, 1890-1891 (1891), p. 77 (Pelew); Oustalet, Nouv. Arch. Mus. Hist. Nat. Paris, (3), 8, 1896, p. 60 (Saypan, Palaos, Ruk, Luganor, Nukuor, Ponapé, Kuschai, Bonham); Hartert, Novit. Zool., 5, 1898, p. 68 (Marianne); Seale, Occ. Papers Bernice P. Bishop Mus., 1, 1901, p. 20 (Saipan?); Safford, Osprey, 1902, p. 66 (Marianas); idem, The Plant World, 7, 1904, p. 267 (Guam); Schnee, Zool. Jahrbücher, 20, 1904, p. 390 (Marschall-Inseln); Safford, Contr. U. S. Nat. Herb., 9, 1905, p. 80 (Guam); Cox, Island of Guam, 1917, p. 22 (Guam).
Micranous leucocapillus Saunders, Cat. Birds British Mus., 25, 1896, p. 145 (Pelew, Caroline Islands); Nehrkorn, Kat. Eiers., 1899, p. 222 (Kusai); Hartert, Novit. Zool., 7, 1900, p. 9 (Ruk); Takatsukasa and Kuroda, Tori, 1, 1915, p. 51 (Pelew).
Megalopterus minutus marcusi Mathews, Birds Australia, 2, 1912, p. 423 (Marianas?); Ridgway, Bull. U. S. Nat. Mus., 50, pt. 8, 1919, p. 553 (Mariannes?); Mathews, Syst. Avium Australasianarum, 1, 1927, p. 146 (Mariannes); Hachisuka, Birds Philippines, 2, 1932, p. 343 (Mariannes).
Megalopterus tenuirostris leucocapillus Kuroda, in Momiyama, Birds Micronesia, 1922, p. 50 (Saipan, Pelew, Ruk, Ponapé, Kusaie).
Megalopterus minutus minutus Fisher and Wetmore, Proc. U. S. Nat. Mus., 79, 1931, p. 45 (Caroline Islands).
Anous minutus worcesteri Yamashina, Tori, 7, 1932, p. 409 (Coror, Namo, Iringlab); Hand-list Japanese Birds, rev., 1932, p. 195 (Saipan, Babelthuap, Koror, Truk, Ponapé, Kusaie, Ebon, Namorik, Jaluit, Elmore, Mille, Aurh, Wotze, Ailuk); Yamashina, Tori, 10, 1940, p. 678 (Assongsong, Saipan); Hand-list Japanese Birds, 3d ed., 1942, p. 219 (Assongsong, Saipan, Babelthuap, Koror, Peliliu, Truk, Ponapé, Kusaie, Ebon, Namorik, Jaluit, Elmore, Mille, Aurh, Wotze, Ailuk).
Anous minutus marcusi Peters, Check-list Birds World, 2, 1934, p. 347 (Caroline Islands).
Anous minutus Bequaert, Mushi, 12, 1939, p. 82 (Ponapé); idem, Occ. Papers Bernice P. Bishop Mus., 16, 1941, p. 253 (Ponapé, Palau).
Anous tenuirostris marcusi Mayr, Birds Southwest Pacific, 1945, p. 27 (Micronesia); Baker, Smithson. Misc. Coll., vol. 107, no. 15, 1948, p. 56 (Peleliu, Ulithi, Truk).
Geographic range.—Marcus, Wake, and Micronesia. In Micronesia: Mariana Islands—Asuncion, Saipan, Guam?; Palau Islands—Babelthuap, Koror, Peleliu; Caroline Islands—Ulithi, Truk, Ponapé, Luganor, Nukuor, Wolea; Marshall Islands—Ebon, Namorik, Jaluit, Elmore, Mille, Aurh, Wotze, Ailuk.
Characters.—Adult: A small tern with sooty-black plumage, grayer on rump and tail; forehead and crown white becoming grayer on nape to merge with blackish on shoulder; narrow, black superciliary stripe; lores black, lower eyelid with white streak, upper eyelid with white spot. Resembles A. t. melanogenys but wing and tail longer and superciliary stripe narrower. Resembles A. t. minutus but with narrower, black superciliary stripe.
abruptly at nape, with mottling in some birds; plumage of body with brownish wash.
Measurements.—Measurements are listed in [table 22].
Specimens examined.—Total number, 51 (27 males, 22 females, 2 unsexed), as follows: Mariana Islands, AMNH—Asuncion, 1 (Jan. 18); Palau Islands, USNM—Peleliu, 2 (Sept. 9, 12); AMNH—exact locality not given, 2 (Nov. 3); Caroline Islands, USNM—Ulithi, 4 (Aug. 20); AMNH—Truk, 5 (Nov. 16, 21, 22)—Ponapé, 15 (Dec. 15)—Kusaie, 17 (Jan. 10, March 10-30, April 1-10); Marshall Islands, USNM—Bikini, 4 (May 2, 14); AMNH—no locality given, 1 (Sept. 3).
Table 22. Measurements of Anoüs tenuirostris of the Pacific Area
Location No. Wing Tail Exposed
culmenAnoüs tenuirostris melanogenys
Hawaiian Islands29 222 113 41 210-229 105-120 41-48 Anoüs tenuirostris marcusi
Hawaiian Islands8 227 118 45 218-231 112-124 44-48 Mariana Islands 1 223 117 44 Palau Islands 3 228 122 43 227-228 117-126 41-45 Caroline Islands 32 229 120 44 220-240 113-127 40-47 Marshall Islands 5 224 118 44 222-229 114-123 41-46 Anoüs tenuirostris minutus
Hawaiian Islands13 227 120 44 220-234 108-128 41-46 Phoenix, Howland, Union, Danger,
Suvarov Islands9 229 119 46 226-233 113-124 42-48 Anoüs tenuirostris minutus
Marquesas Islands10 226 117 45 220-233 115-124 42-48 Tuamotu Archipelago 17 229 118 45 222-234 112-126 42-47 Society, Cook, Austral Islands 12 230 118 46 223-238 114-120 43-47 Samoa, Fiji, Tonga Islands 6 228 118 44 224-231 115-121 42-47 Kermadec, Norfolk Isl'ds,
New Zealand15 226 116 44 219-235 112-121 42-47 New Hebrides, Solomon, Bismarck,
Admiralty Islands, New Guinea34 229 117 43 222-237 109-130 40-46 Anoüs tenuirostris diamesus
Marquesas Islands14 230 120 44 224-237 114-127 41-47 Nesting.—Few reports have been obtained concerning the nesting of the White-capped Noddy in Micronesia. Finsch (1881b:107) recorded nests, and Nehrkorn (1899:222) reported on eggs taken at Kusaie. Yamashina (1932a:409) recorded the taking of eggs at Koror in the Palau Islands on January 19 and November 10 and in the Marshalls at Namo on October 19, and at Iringlab on October 21. No evidence of nestings was obtained by the NAMRU2 party in 1945, although a number of birds were seen at Ulithi in August. Coultas (field notes) writes that a colony of approximately 20 birds began nesting about Christmas time on a small offshore island near Ponapé. Nests were placed in the crotches of limbs of mangroves, 8 to 15 feet above the ground.
Food habits.—The NAMRU2 party found small fish in the stomachs of terns taken at Ulithi and Peleliu.
Parasites.—Bequaert (1939:82 and 1941:253) records the fly (Hippoboscidae), Alfersia aenescens, from the White-capped Noddy taken at Ponapé and Palau.
Remarks.—The subspecies of Anoüs tenuirostris are well differentiated by color and to a lesser extent by measurements. [Table 22] lists measurements which show that the Hawaiian subspecies, A. t. melanogenys, has the shortest wing and the shortest tail whereas the subspecies from Cocos and Clipperton islands, A. t. diamesus, has the longest wing and the longest tail. The exposed culmen varies in length but little among the four subspecies. The systematic position of A. t. worcesteri from Cavilli Island in the Sula Sea has not been determined because of lack of material. In the third edition of the Hand-list of Japanese Birds (Hachisuka et al., 1942:219) the birds from Micronesia are referred to A. t. worcesteri as they are also in other recent publications by the Japanese. Specimens from the Philippines are needed for examination to determine satisfactorily the subspecies status of the birds under consideration.
Field observations indicate that the White-capped Noddy is not abundant in the Mariana Islands. According to Oustalet (1896:60), Marche obtained a female at Saipan in June, 1888, and Yamashina (1940:678) records five adults from Assongsong (Asuncion). Owston's collectors obtained a specimen at Asuncion on January 18, 1904. In the Palaus, Carolines, and Marshalls birds of this species are numerous and have been observed or collected at many of the islands. Coultas with the Whitney South Sea Expedition obtained specimens at Kusaie, Ponapé and Palau. He found them along the shores of the large islands and, especially, on the smaller offshore islets. At Ulithi Atoll in August, 1945, the NAMRU2 party observed small flocks of four to ten individuals flying offshore and feeding inside the reef. They were frequently observed in company with Sterna sumatrana. Fewer birds were seen in September, 1945, at the Palau Islands by the NAMRU2 party.
Gygis alba candida (Gmelin)
White Tern
Sterna candida Gmelin, Syst. Nat., 1, pt. 2, 1789, p. 607. (Type locality, Christmas Island.)
Gygis candida Finsch, Ibis, 1880, p. 220 (Taluit); Saunders (part), Cat. Birds British Mus., 25, 1896, p. 149 (Marshalls); Schnee, Zool. Jahrbücher, 20, 1904, p. 390 (Marschall-Inseln).
Gygis alba Finsch, Ibis, 1880, pp. 330, 332 (Taluit); Wiglesworth (part), Abhandl. und Ber. Zool. Mus. Dresden, no. 6, 1890-1891 (1891), p. 78 (Marshalls); Oustalet (part), Nouv. Arch. Mus. Hist. Nat. Paris, (3), 8, 1896, p. 58 (Saypan, Pagan, Agrigan, Marshalls); Safford, Guam, 1912, p. 19 (Guam); Strophlet, Auk, 63, 1946, p. 537 (Guam); Baker, Condor, 49, 1947, p. 125 (Guam); Stott, Auk, 64, 1947, p. 525 (Saipan); Baker (part), Smithson. Misc. Coll., vol. 107, no. 15, 1948, p. 57 (Guam, Rota, Saipan).
Gygis alba kittlitzi Hartert, Novit. Zool., 5, 1898, p. 67 (Saipan, Guam); Seale, Occ. Papers Bernice P. Bishop Mus., 1, 1901, p. 21 (Guam); Safford, Osprey, 1902, 66 (Marianas); idem, The Plant World, 7, 1904, p. 267 (Guam); idem, Contr. U. S. Nat. Herb., 9, 1905, p. 80 (Guam); Mathews (part), Birds Australia, 2, 1912, p. 443 (Marianas); Prowazek, Die deutschen Marianen, 1913, p. 100 (Marianan); Cox, Island of Guam, 1917, p. 22 (Guam); Ridgway (part), Bull. U. S. Nat. Mus., 50, pt. 8, 1919, p. 559 (Mariannes); Kuroda, Avifauna Riu Kiu, 1925, p. 193 (?Mariannes); Yamashina, Tori, 7, 1931, p. 410 (Saipan); Yamashina, Tori, 7, 1932, p. 409 (Iringlab, Namo, Aruno); Hand-list Japanese Birds (part), rev., 1932, p. 196 (Guam, Tinian, Saipan, Pagan, Agrigan, Jaluit, Mille, Aurh, Wotze, Likieb, Mejit); Yamashina (part), Tori, 10, 1940, p. 678 (Assongsong).
Gygys alba Wheeler, Report Island of Guam, 1900, p. 13 (Guam).
Gygis albus kittlitzi Kuroda (part), in Momiyama, Birds Micronesia, 1922, p. 50 (Guam, Saipan, Pagan, Agrigan, Marshalls).
Leucanous albus kittlitzi Mathews (part), Syst. Avium Australasianarum, 1, 1927, p. 143 (Marianne).
Gygis alba microrhyncha La Touche (part), Handbook Birds Eastern China, 2, 1933, p. 335 (Marianne).
Gygis alba candida Bryan, Guam Rec., vol. 13, no. 2, 1936, p. 24 (Guam); Hand-list Japanese Birds (part), 3d ed., 1942, p. 219 (Guam, Tinian, Saipan, Pagan, Agrigan, Assongsong, Jaluit, Mille, Aurh, Wotze, Likieb, Mejit); Downs, Trans. Kansas Acad. Sci., 49, 1946, p. 94 (Tinian); Borror, Auk, 64, 1947, p. 417 (Agrihan).
Geographic range.—Northern Pacific from Bonins and Marianas east to Wake and Hawaiian Chain, south to Marshall, Phoenix, Christmas and Fanning islands (see [figure 12]). In Micronesia: Mariana Islands—Guam, Rota, Tinian, Saipan, Pagan, Agrihan; Marshall Islands—Jaluit, Mille, Aurh, Wotze, Likieb, Mejit, Eniwetok, Bikini, Kwajalein.
Characters.—Adult: A small tern with ivory-white plumage except for black, narrow, orbital ring; shafts of primary quills dark brown; shafts of tail feathers blackish; bill black with bluish base; tarsus dark bluish with yellowish webs; iris and skin black.
Immature: Resembles adult, but with light brown mottlings on upper parts, especially on the mantle; feathers softer, bill shorter.
Measurements.—Measurements are listed on [table 23].
Weights.—The NAMRU2 party obtained weights of 11 adult males from Guam and Rota as 110 (97-124); weights of 6 adult females from Guam as 108 (100-116). These specimens were taken from May to October, 1945.
Specimens examined.—Total number, 41 (23 males, 14 females, 4 unsexed), as follows: Mariana Islands, USNM—Guam, 20 (May 24, 29, June 6, 8, 14, 15, 16, 18, 23, July 10, 19, 20)—Rota, 2 (Oct. 19, 27)—Saipan, 1 (Sept. 26); AMNH—Guam, 4 (March 7, 9, 20)—Tinian, 1 (Sept. 8)—Asuncion, 4 (Jan. 1, 18, 25); MCZ—Saipan, 3 (Jan. 7, March 20, April 17); Marshall Islands, USNM—Bikini, 6 (Feb. 27, March 2, 16, 19).
>Nesting.—Gygis alba does not construct a nest but places its single egg rather precariously in the crotch of a branch in a tree (or on rock). In Micronesia nesting activities have been observed at various times of the year. Yamashina (1932a:409, 410) reported on eggs taken in the Marianas at Saipan on February 2 and in the Marshalls at Arhno on September 26, at Iringlab on October 21 and at Namo on October 19. At Guam a pair of White Terns was seen in a large tree on March 27, 1945, by the NAMRU2 observers. Because of their behavior, it was suspected that they had an egg or young in the tree. Further inspection revealed, on March 31, a downy young sitting in the tree. The young bird was attended by the parents until it began to fly on April 17. Hartert (1898:68) reports that eggs of the White Tern were taken at Saipan on July 28 and August 11. Morrison obtained a male nestling on March 16 and eggs on March 22 at Bikini in 1946.
Remarks.—The White Tern is usually restricted to the remote islands in the Pacific, Indian and South Atlantic oceans; there, according to the latest treatment, which is that of Peters (1934:348, 349), six subspecies are recognized. In studying the geographical variation of the species, the writer has examined 595 adult specimens, including previously unstudied material collected by the Whitney South Sea Expedition, which is deposited in the American Museum of Natural History.
This ivory-white species presents an unusual problem in that there are few characters available to distinguish the subspecies. Measurements of taxonomic value include those of the wing, tail, exposed culmen, and depth and the shape of the culmen. There appears to be no significant secondary sexual difference between males and females, and measurements of the two sexes are combined. The chief problem within this species seems to hinge on how to classify isolated, but relatively similar, populations. The examination of the large series of specimens from the Whitney collections has yielded more complete information to assist in the solution of this problem.
Gygis alba alba (Sparrman) of the South Atlantic Ocean (Fernando de Noronha, South Trinidad, Ascension, and St. Helena islands) and G. a. monte Mathews of the Indian Ocean (Seychelles, Aldabra, Mascarene and Chagos islands) are isolated populations. Specimens examined are those which have previously been studied by other workers; measurements are shown in [table 23].
With the exception of G. a. microrhyncha, G. a. monte has the smallest average length of wing of all of the subspecies of G. alba. In G. a. alba the length of wing as well as most of the other measurements differ but slightly from those of some of the populations in the Pacific area although the slender bill of the Atlantic bird is a distinctive character, as pointed out by Murphy (1936:1166).
Table 23. Measurements of Subspecies of Gygis alba From the Atlantic and Indian Ocean Area
Subspecies No. Wing Longest
tail
featherShortest
tail
featherExposed
culmenDepth
culmenTarsus Gygis alba alba 24 246 99 71 40 8.0 14.5 239-256 93-111 68-77 35-44 7.5-9.0 13.0-16.5 Gygis alba monte 35 232 106 71 39 8.5 13.5 224-244 98-116 64-81 37-44 8.0-8.5 12.5-14.0 The taxonomic position of the White Terns of the Pacific area has been one of uncertainty for a long time; as Peters (1934:349) puts it, "It is obvious that the last word on the Pacific races of Gygis has not yet been said." A principal feature of the problem in this region is the presence in the Marquesas of a well-marked subspecies, G. a. microrhyncha, virtually surrounded by a wide-ranging and relatively undifferentiated form, G. a. pacifica (Lesson) (see [figure 12]). The small cormorant (Phalacrocorax melanoleucus brevicauda Mayr) from Rennell Island, Solomons, is another example of a distinct form surrounded by a widely distributed subspecies.
In all, 55 adult specimens of G. a. microrhyncha have been examined from the following islands in the Marquesas Group: Mukahiva, Eiau, Motane, Hivaoa, Uapu, Tahuata, Uahuka, Fatuhiva. The measurements are listed in [table 24], and show that the White Tern in the Marquesas is a much smaller bird than the other subspecies and has a shorter bill, wing, and tail. The tail possesses a shallow fork as compared with the deeper fork of the tail of other subspecies. In addition, the depth of the culmen averages two millimeters less in the subspecies in the Marquesas. The presence of a wider, black eye-ring is also a distinguishing character in this subspecies.
Gygis a. microryhncha was for a long time treated as a species distinct from G. alba but has recently been considered as a subspecies G. alba by Peters and others. On the islands of Hatutu and Motane in the Marquesas, the Whitney South Sea Expedition obtained some birds which appear to be intergrades between the two subspecies of White Terns in the area. The measurements of nine birds which show intergradation between G. a. microrhyncha and G. a. pacifica are listed in [table 24]. Probably the Marquesas population is tending toward complete reproductive isolation.
Fig. 12. Geographic distribution of Gygis alba in the Pacific area. (1) G. a. candida; (2) G. a. pacifica; (3) G. a. microrhyncha; (4) G. a. royana.
Table 22. Measurements of Anoüs tenuirostris of the Pacific Area
Table 22. Measurements of Anoüs tenuirostris of the Pacific Area
| Location | No. | Wing | Tail | Exposed culmen |
| Anoüs tenuirostris melanogenys Hawaiian Islands | 29 | 222 | 113 | 41 |
| 210-229 | 105-120 | 41-48 | ||
| Anoüs tenuirostris marcusi Hawaiian Islands | 8 | 227 | 118 | 45 |
| 218-231 | 112-124 | 44-48 | ||
| Mariana Islands | 1 | 223 | 117 | 44 |
| Palau Islands | 3 | 228 | 122 | 43 |
| 227-228 | 117-126 | 41-45 | ||
| Caroline Islands | 32 | 229 | 120 | 44 |
| 220-240 | 113-127 | 40-47 | ||
| Marshall Islands | 5 | 224 | 118 | 44 |
| 222-229 | 114-123 | 41-46 | ||
| Anoüs tenuirostris minutus Hawaiian Islands | 13 | 227 | 120 | 44 |
| 220-234 | 108-128 | 41-46 | ||
| Phoenix, Howland, Union, Danger, Suvarov Islands | 9 | 229 | 119 | 46 |
| 226-233 | 113-124 | 42-48 | ||
| Anoüs tenuirostris minutus Marquesas Islands | 10 | 226 | 117 | 45 |
| 220-233 | 115-124 | 42-48 | ||
| Tuamotu Archipelago | 17 | 229 | 118 | 45 |
| 222-234 | 112-126 | 42-47 | ||
| Society, Cook, Austral Islands | 12 | 230 | 118 | 46 |
| 223-238 | 114-120 | 43-47 | ||
| Samoa, Fiji, Tonga Islands | 6 | 228 | 118 | 44 |
| 224-231 | 115-121 | 42-47 | ||
| Kermadec, Norfolk Isl'ds, New Zealand | 15 | 226 | 116 | 44 |
| 219-235 | 112-121 | 42-47 | ||
| New Hebrides, Solomon, Bismarck, Admiralty Islands, New Guinea | 34 | 229 | 117 | 43 |
| 222-237 | 109-130 | 40-46 | ||
| Anoüs tenuirostris diamesus Marquesas Islands | 14 | 230 | 120 | 44 |
| 224-237 | 114-127 | 41-47 |
Table 23. Measurements of Subspecies of Gygis alba From the Atlantic and Indian Ocean Area
Table 23. Measurements of Subspecies of Gygis alba From the Atlantic and Indian Ocean Area