Whistling Heron is a medium sized heron with relatively short tarsi. Among its most distinctive features are the thick bill, which is pink with a black tip, and the bright blue bare skin on the lores and surrounding the eyes. The crown is black, but the sides of the head, and the entire neck and breast, are yellowish buff. The back and wings mostly are gray, with buff tips to the wing coverts. The rump and uppertail coverts are white. The belly and undertail coverts are white.
Whistling Heron is not particularly similar to any other species; it has a distinctive color pattern to the plumage, and striking soft part colors on the face and bill.
The following description is based on Blake (1977):
Adult: Sexes similar. Crown dull black or slaty, with several plumes (up to 4 cm long) on the nape, plumes black tipped with buff or white. Sides of head, entire neck, and breast yellowish buff or pale tawny. Back, scapulars, and remiges pale bluish slate, remiges darker on inner webs of primaries. Upper wing coverts pinkish cinnamon, with black streaks. Uppertail coverts and rectrices white. Belly and sides white.
Humphrey and Parkes (1963) noted that in life (or in their case, in a freshly collected specimen), the rump, breast, belly and flanks are light yellow; this color fades to white in "after several months to a year". On the other hand, the tawny buff of the neck and of the wing coverts does not fade after death.
Immature: Upperparts generally dull gray; crown and remiges slaty. Wing coverts narrowly striped with pale cinnamon. Neck, breast, and center of belly light gray and vaguely streaked. As in adults, the throat, sides, belly, tail, and tail coverts are white.
Nestling: Completely pale brown bill and gray head, with a pale pink bill with a dark brown tip (Kushlan et al. 1982).
Little known, other than the description by Humphrey and Parkes (1963). The first prebasic molt is initiated before the juvenile remiges and rectrices are completely grown. This molt includes most of the body plumage, and the upper wing coverts, but not the remiges.
The first prealternate molt apparently involves feathers of the crown (including the crest) and neck, and perhaps elsewhere on the body.
The definitive prebasic molt is complete. Humphrey and Parkes (1963) also suspected that there was a definitive prealternate molt, involving the crown (and crest) and the neck, but apparently they did not find conclusive evidence for this molt.
Iris: white, very pale yellow
Bill: bright red or bright pink, with black tip; sometimes there is a white band between the pink base and the black tip
Facial skin (lores and surrounding eye): bright blue, light blue
Tarsi and toes: blackish, black
Bare parts color data from Friedmann and Smith (1950) and Belton (1984).
Total length: 50-58 cm (Blake 1977), 53-58 cm (Hilty 2003)
Linear measurements (from Blake 1977):
male, sibilatrix (n = 9)
wing length (flat), mean 296.8 mm (range 282-314 mm)
bill length (exposed culmen), mean 66.5 mm (range 61-72 mm)
female, sibilatrix (n = 6)
wing length (flat), mean 292 mm (range 283-301 mm)
bill length (exposed culmen), mean 61.7 mm (range 59-65 mm)
male, fostersmithi (n = 2)
wing length (flat), mean 295.5 mm (280, 311 mm)
bill length (exposed culmen), mean 69.5 mm 65, 74 mm)
female, fostersmithi (n = 2)
wing length (flat), mean 310 mm (307, 313 mm)
bill length (exposed culmen), mean 71.5 mm (69, 74 mm)
Mass: 1 female, 370 g (Belton 1984); 1 female, 550 g (Contreras 1983)