Immature: Resembles adult, but forehead mottled white and brown, with sides of head less distinctly speckled with brown; crown, neck and upper back dusky brown; back, scapulars and upper tail-coverts olivaceous-brown; chin and throat whitish; breast feathers pearly-gray tipped with white; abdomen white; sides gray, washed with buff. Older birds are darker above and more brownish-gray below; frontal shield small.
G. c. guami resembles G. c. indica, but upper wing-coverts darker and near "olivaceous black"; back, rump and scapulars darker and less olivaceous brown, although not so dark as in G. c. orientalis. From G. c. lozanoi, G. c. guami differs in: slightly darker upper wing-coverts; richer olivaceous-brown on back, scapulars and rump; thinner culmen with possibly less yellow coloring on tip. G. c. guami resembles G. c. sandvicensis Streets of the Hawaiian Islands, but has less olive wash on the feathers and a smaller frontal shield.
Measurements.—Measurements of Gallinula chloropus are presented in table 18. In general, females are smaller than males.
Table 18. Measurements of Gallinula chloropus
Table 18. Measurements of Gallinula chloropus
| Location | No. | Wing | Bill from rictus | Bill from nostril | Tarsus |
| G. c. indica | 15 | 164 | 27 | 14.4 | 48 |
| 158-173 | 24-29 | 13.1-18.1 | 44-50 | ||
| G. c. orientalis | 3 | 152 | 27 | 13.8 | 45 |
| 146-152 | 26-29 | 13.1-14.4 | 44-46 | ||
| G. c. lozanoi | 11 | 164 | 27 | 14.5 | 50 |
| 153-170 | 24-29 | 13.1-15.2 | 45-57 | ||
| G. c. guami | 11 | 164 | 27 | 14.7 | 49 |
| 156-171 | 24-28 | 13.1-16.2 | 47-56 | ||
| G. c. sandvicensis | 2 | 150-158 | 27 | 13.4 | 52-56 |
Weights.—From Guam an adult male weighed 291 grams and an adult female 256 (Baker, 1948:49).
Specimens examined.—Total number, 42 (16 males, 22 females, 4 unsexed), as follows: Mariana Islands, USNM—Guam, 5 (Feb. 24, May, June 5, 7, 18—Tinian, 3 (Oct. 12, 18)—Saipan, 3 (Sept. 28, 30); AMNH—Guam, 25 (Feb. 21, April 6, July 13, 28, 30, Aug. 1, 3, 6, 7, 13, 19, 23, 30, 31, Sept. 3, 17, Dec. 11—Tinian, 5 (June 11, Sept. 12, 13, 14).
Nesting.—Hartert (1898:63) reports nests of the Gallinule at Guam in grass and on swampy ground in December and March. A male with enlarged gonads was taken by the NAMRU2 party at Guam on June 7. Marshall (1949:219) is of the opinion that this bird breeds all year.