The Avifauna of Micronesia, Its Origin, Evolution, and Distribution

by Rollin H. Baker

Demigretta sacra sacra (Gmelin)

Reef Heron

Ardea sacra Gmelin, Syst. Nat., 1, pt. 2, 1789, p. 640. (Type locality, Tahiti.)

Ardea jugularis Kittlitz, Observ. Zool., in Lutké, Voy. "Le Séniavine," 3, 1836, pp. 286, 299, 304 (Ualan, Lougounor, Guahan); Hartlaub, Journ. f. Ornith., 1854, p. 167 (Mariannen); Kittlitz, Denkw. Reise russ. Amer. Micron. und Kamchat., 2, 1858, p. 63 (Ualan); Pelzeln, Reise "Novara," Vögel, 1865, pp. 118, 162, 120, 121 (Puynipet, Ualan).

Ardea (Herodias) atra Gray, Cat. Birds Trop. Is. Pacific Ocean, 1859, p. 48 (Ladrone or Marian Islands, Caroline Islands).

Ardea sacra Hartlaub, Proc. Zool. Soc. London, 1867 (1868), p. 831 (Matelotas Islands); Hartlaub and Finsch, Proc. Zool. Soc. London, 1868, pp. 8, 118 (Pelews); Finsch and Hartlaub, Journ. f. Ornith., 1870, p. 137 (Pelews, Matelotas); Gray, Hand-list Birds, 3, 1871, p. 28 (Marian, Carolines, Pelews, Matelotas); Hartlaub and Finsch, Proc. Zool. Soc. London, 1872, pp. 89, 104 (Pelew, Uap, Ualan); Gräffe, Journ. Mus. Godeffroy, 2, 1873, p. 123 (Yap); Finsch, Journ. Mus. Godeffroy, 8, 1875, pp. 5, 32 (Palau); idem, Journ. Mus. Godeffroy, 12, 1876, pp. 18, 38 (Ponapé, Ualan); idem, Proc. Zool. Soc. London, 1877 (1878), p. 781 (Ponapé); idem, Journ. f. Ornith., 1880, pp. 294, 306 (Ponapé, Kuschai); idem, Ibis, 1880, pp. 220, 330, 332 (Taluit); idem, Proc. Zool. Soc. London, 1880, p. 577 (Ruk); idem, Ibis, 1881, pp. 105, 106, 109, 115 (Kushai, Ponapé); Schmeltz and Krause, Ethnogr. Abth. Mus. Godeffroy, 1881, pp. 299, 353 (Mortlocks, Ruk); Finsch, Mitth. Ornith. Ver. Wien, 1884, p. 51 (Jaluit, Kuschai); Oustalet, Le Nat., 1889, p. 261 (Mariannes); Wiglesworth, Ibis, 1893, p. 211 (Marshalls); Oustalet, Nouv. Arch. Mus. Hist. Nat. Paris, (3), 8, 1896, p. 36 (Guam, Marshalls, Palaos, Carolines); Schnee, Zool. Jahrbücher, 20, 1904, p. 390 (Marschall-Inseln).

Demiegretta sacra Salvadori, Ornith. Papuasia, 3, 1882, p. 348 (Marshalls, Ualan, Ponapé, Ruck, Pelew, Mariannis); Wiglesworth, Abhandl. Ber. Zool. Mus. Dresden, no. 6, 1890-1891 (1891), p. 67 (Marianne, Pelews, Luganor, Ruk, Ponapé, Ualan, Taluit); Hartert, Novit. Zool., 5, 1898, p. 64 (Saipan); Sharpe, Cat. Birds British Mus., 26, 1898, p. 137 (Pelew, Carolines, Marshalls); Hartert, Novit. Zool., 7, 1900, p. 11 (Ruk); Seale, Occ. Papers Bernice P. Bishop Mus., 1, 1901, p. 29 (Guam); Safford, Osprey, 1902, p. 67 (Marianas); idem, The Plant World, 7, 1904, p. 266 (Guam); Kuroda, Avifauna Riu Kiu, 1925, p. 129 (Micronesia); Bryan, Guam, Rec., vol. 13, no. 2, 1936, p. 15 (Guam); Bequaert, Occ. Papers Bernice P. Bishop Mus., 16, 1941, p. 266 (Kusaie).

Demigretta sacra Safford, Contr. U. S. Nat. Herb., 9, 1905, p. 79 (Guam); Prowazek, Die deutschen Marianen, 1913, p. 101 (Saipan, Tinian); Cox, Island of Guam, 1917, p. 21 (Guam); Bequaert, Mushi, 12, 1939, p. 81 (Kusaie); Warton, Ecol. Monogr., 16, 1946, p. 175 (Guam); Warton and Hardcastle, Journ. Parasitology, 32, 1946, pp. 306, 316 (Ulithi, Guam).

Demiegretta jugularis Takatsukasa and Kuroda, Tori, 1, 1915, p. 50 (Truk, Ponapé, Pelew).

Demiegretta jugularis grayi Uchida, Annot. Zool. Japon., 9, 1918, pp. 484, 488, 490 (Ponapé).

Demiegretta sacra sacra Kuroda, in Momiyama, Birds Micronesia, 1922, p. 36 (Guam, Saipan, Angaur, Luganor, Yap, Ngoli, Ruk, Ponapé, Kusaie, Taluit).

Demigretta sacra sacra Wetmore, in Townsend and Wetmore, Bull. Mus. Comp. Zoöl., 63, 1919, p. 171 (Kusaie); Mathews, Syst. Avium Australasianarum, 1, 1927, p. 198 (Carolines); Yamashina, Tori, 7, 1932, p. 406 (Ponapé); Hand-list Japanese Birds, rev., 1932, p. 183 (Saipan, Guam, Babelthuap, Peliliu, Angaur, Ngulu, Yap, Truk, Lukunor, Ponapé, Kusaie, Jaluit, Majuro); Mayr and Amadon, Amer. Mus. Novit., no. 1144, 1941, p. 10 (Guam, Saipan, Palau, Ponapé, Kusaie, Ruk, Tah); Hand-list Japanese Birds, 3d ed., 1942, p. 203 (Saipan, Rota, Babelthuap, Peliliu, Angaur, Ngulu, Yap, Ulithi, Truk, Lukunor, Ponapé, Kusaie, Jaluit, Arhno, Majuro, Moloclab, Wotze, Likieb, Ailuk); Mayr, Birds Southwest Pacific, 1945, pp. 51, 284 (Micronesia); Downs, Trans. Kansas Acad. Sci., 49, 1946, p. 90 (Tinian); Strophlet, Auk, 63, 1946, p. 535 (Guam); Borror, Auk, 64, 1947, p. 417 (Agrihan); Stott, Auk, 64, 1947, p. 524 (Saipan); Baker, Smithson. Misc. Coll., vol. 107, no. 15, 1948, p. 42 (Rota, Guam, Peleliu, Ulithi, Truk).

Demigretta sacra micronesiae Momiyama, Tori, 5, no. 22, 1926, p. 110 (Type locality, Caroline Islands; Pelew, Yap, Truk, Ponapé, Kusaie).

Geographic range.—Coasts of Asia and adjacent islands from Korea and Japan south to Malaysia, Australia, Melanesia, Polynesia and Micronesia. In Micronesia: Mariana Islands—Agrigan, Tinian, Saipan, Rota, Guam; Palau Islands—Babelthuap, Koror, Garakayo, Ngesebus, Peleliu, Ngabad, Anguar; Caroline Islands—Ulithi, Yap, Ngulu, Truk, Lukunor, Ponapé, Kusaie; Marshall Islands—Jaluit, Arhno, Majuro, Maloclab, Wotze, Likieb, Ailuk, Bikini, Eniwetok, Kwajalein.

Characters.—A medium-sized heron with three color phases: in gray phase color of body varies from "deep blackish-slate" to light bluish-slate, particularly on the breast, with a white gular stripe; wear and fading causes the color of the body to change to brownish-slate; bluish-gray ornamental plumes may be present on adult; in white phase color of body is pure white in adult stage; plumage of immature may be mottled; in mottled phase there may be a variable amount of gray and white (for complete study of plumages of Demigretta sacra see Mayr and Amadon, 1941:4).

Measurements.—Mayr and Amadon (1941:1) record the length of the wing of thirty adults from the Marianas and Carolines as 268-309 (284). Seven adult males obtained by the NAMRU2 party at Rota, Guam and Peleliu measure: wing, 287-307 (294); tail, 95-114 (101); culmen, 91-101 (96); tarsus, 78-87 (82); seven adult females, from Rota and Guam: wing, 265-285 (275); tail, 87-96 (91); culmen, 86-92 (89); tarsus, 72-79 (76).

Weights.—The author (1948:42) lists the following weights: four adult males from Guam (gray phase) 590-667 (614); two adult males from Guam (white phase) 600 and 662; five adult females from Guam and Rota (gray phase) 477-553 (506).

Specimens examined.—Total number, 80 (38 males, 40 females, 2 unsexed) as follows: Mariana Islands, USNM—Rota, 3 (Oct. 18, Nov. 2, 5)—Guam, 21 (May 11, June 6, 18, July 6, 8, 16, 24, 27, Aug. 6, 8, 27); AMNH—Saipan, 2 (July 22)—Guam, 9 (Feb. 11, Mar. 6, 7, April 11, Aug. 15, Sept. 14, 16, Nov. 27, Dec. 20); Palau Islands, USNM—Peleliu, 3 (Sept. 10, 16); AMNH—exact locality not given, 5 (Nov. 8, 21, 23); Caroline Islands, USNM—Ulithi, 1 (Aug. 15)—Kusaie, 1 (Feb. 8); AMNH—Truk, 3 (Feb. 18, May 20, Nov. 5)—Tah, 2 (Oct. 18)—Ponapé, 2 (Nov. 21, undated)—Kusaie, 26 (Jan. 25, 26, Feb., Mar. 10-20, 20-30, April 1-10, 18); Marshall Islands, USNM—Bikini, 2 (March 29, April 2).

Nesting.—The Reef Heron apparently nests on most of the islands in Micronesia. The eggs are laid in a nest of grass and twigs on or near the ground. Hartert (1898:64) records a nest found in grass at Saipan on July 28, 1895. Yamashina (1932a:406) reports on one egg taken at Ponapé on July 23, 1931. Marshall (1949:219, fig. 37) found a breeding bird in April at Tinian. Coultas (field notes) learned from the natives at Ponapé that the Reef Heron builds a nest of small sticks near the ground in the mangrove thickets. Two or three eggs are laid, and nests can be found at various times of the year. Mayr and Amadon (1941:4) comment on the prolonged breeding season and report six sets of eggs from Polynesia taken in January, March, April, September, October, and November.

Food habits.—The author (1948:42) found fish and crabs in the stomachs of birds taken at Guam, Ulithi and Peleliu.

Parasites.—Uchida (1918:484, 488, 490) found the following bird lice (Mallophaga) on the Reef Heron at Ponapé: Nirmus orarius, Colpocephalum importunum, and Myrsidea teraokai. Bequaert (1939:81 and 1941:266) found the fly (Hippoboscidae), Ornithoctona plicata, on the heron at Kusaie. Wharton (1946:175) and Wharton and Hardcastle (1946:306, 316) obtained chiggers (Acarina), Neoschöngastia egretta and N. carveri, from the Reef Heron at Guam and Ulithi.

Remarks.—The species Demigretta sacra contains two subspecies, the widespread D. s. sacra and a larger form, D. s. albolineata (Gray), known from New Caledonia and the Loyalty Islands. The latter subspecies is surrounded by the former, a distribution which closely parallels that in each of the species Phalacrocorax melanoleucus and Gygis alba of Oceania. Recently Delacour (in Delacour and Mayr, 1945b:105) has dropped the name Demigretta placing all of the forms of this genus in Egretta. He says, "We cannot accept the genus Demigretta, which is based on the more extended feathering of the tibia, the different length and texture of the feathers of the trains, the shortness of the tarsus and the presence of a dark gray color phase. The latter exists in the Madagascan and African subspecies of Egretta garzetta."

The Reef Heron is a conspicuous member of the bird life of Micronesia, being recorded from most of the island groups. It prefers the placid and shallow waters of the lagoons and tidal beaches where it obtains the littoral animal life as food. The birds are seldom seen inland and usually frequent the beaches and rocky coasts. In this respect there is little opportunity for competition with the migratory Plumed Egret, which prefers the grassy upland and marsh areas and inland ponds. The Reef Heron is a quiet, usually solitary, and retiring bird, being exceedingly difficult to approach, especially when found on the open tidal flats.

The problem of plumages and color phases in the Reef Heron has been treated by Mayr and Amadon (1941:4-10). Specimens which they examined from Micronesia were found to be 54 percent gray, 40 percent white, and 6 percent mottled. Of the birds obtained by NAMRU2 field parties, fewer than 40 percent were white. Field counts showed a considerable variation in the ratio of grays to whites: Guam—6 grays to 4 whites; Ulithi—4 grays, 6 whites, 1 mottled; Palau—equal number of grays and whites; Truk—2 whites, 1 gray, 1 mottled. For some unknown reason, the gray birds were more easily approached than the white birds. Gleise and Genelly (1945:221) saw one white Reef Heron at Eniwetok. Wallace (field notes) found white herons more numerous than gray ones at Kwajalein in 1944 and 1945. Borror (1947:417) observed gray birds at Agrigan. Stott (1947:524) saw one blue heron on December 24, at Saipan. The 150 birds seen by him at Lake Susupe in December probably were Plumed Egrets.

In discussing the variation in the color phases of the Reef Heron throughout its range, Mayr (1924b:237) suggests that the reduced variability of small populations may not be due to accidental gene loss, but instead to the population having descended from a single pair or from one fertilized female. The descendents would naturally possess only those characters provided for in the genetic make-up of the parents. Reef Herons on New Zealand and in the Marquesas Islands all are gray, while at other island groups different proportions of gray and white individuals occur; such phenomena may result because of the genetic constitution of the "founders."