Blue Whistling Thrush

This whistling thrush is dark violet blue with shiny spangling on the tips of the body feathers other than on the lores, abdomen and under the tail. The wing coverts are a slightly different shade of blue and the median coverts have white spots at their tips. The bill is yellow and stands in contrast. The inner webs of the flight and tail feathers is black. The sexes are similar in plumage. It measures 31–35 cm (12–14 in) in length. Weight across the subspecies can range from 136 to 231 g (4.8 to 8.1 oz). For comparison, the blue whistling thrush commonly weighs twice as much as an American robin. This species is possibly the largest extant thrush though size overlap does occur with the similar by length great thrush and the insular Amami thrush, whose mean body mass falls around the middle of those of the whistling thrush. Among standard measurements, the wing chord can measure 15.5–20 cm (6.1–7.9 in) long, the tarsus is 4.5–5.5 cm (1.8–2.2 in) and the bill is 2.9–4.6 cm (1.1–1.8 in). Size varies across the range with larger thrushes found to the north of the species range and slightly smaller ones to the south, corresponding with Bergmann's rule. In northern China, males and females average 188 g (6.6 oz) and 171 g (6.0 oz), whereas in India they average 167.5 g (5.91 oz) and 158.5 g (5.59 oz). Several populations are given subspecies status. The nominate form with a black bill is found in central and eastern China. The population in Afghanistan, turkestanicus, is often included in the widespread temminckii which has a smaller bill width at the base and is found along the Himalayas east to northern Burma. The population eugenei, which lacks white spots on the median coverts, is found south into Thailand. Cambodia and the Malay peninsula have crassirostris, while dichrorhynchus with smaller spangles occurs further south and in Sumatra. The Javan population, flavirostris, has the thickest bill. The subspecies status of several populations has been questioned.