 The adult of the nominate subspecies is a medium @-@ sized rail , 23 – 28 cm ( 9 @.@ 1 – 11 @.@ 0 in ) long with a 38 – 45 cm ( 15 – 18 in ) wingspan . Males typically weigh 114 – 164 g ( 4 @.@ 0 – 5 @.@ 8 oz ) and females are slightly lighter at 92 – 107 g ( 3 @.@ 2 – 3 @.@ 8 oz ) . The upper parts from the forehead to tail are olive @-@ brown with black streaks , especially on the shoulders . The sides of the head and the underparts down to the upper belly are dark slate @-@ blue , except for a blackish area between bill and eye , and brownish sides to the upper breast . The flanks are barred black and white , and the undertail is white with some darker streaks . The long bill and the iris are red , and the legs are flesh @-@ brown . The sexes are similar ; although the female averages slightly smaller than the male , with a more slender bill , determining sex through measurements alone is unreliable . The juvenile has a blackish crown and a white chin and throat . The underparts are buff or white with darker bars , and the flank markings are brown and buff , rather than black and white . The undertail is buff , and the eye , bill and leg colours are duller than the adult . The downy chick is all black apart from a mainly white bill . After breeding , the rail has an extensive moult , and is flightless for about three weeks . Individual adults can be identified by the markings on the undertail , which are unique to each bird . Adult males have the strongest black undertail streaks . It has been suggested that the dark barring on the undertail of this species is a compromise between the signalling function of a pure white undertail , as found in open water or gregarious species like the common moorhen , and the need to avoid being too conspicuous . 
