Blue whistling thrush

The blue whistling thrush (Myophonus caeruleus) is a bird in the Old World flycatchers family Muscicapidae that is found in the mountains of Central Asia, South Asia, China and Southeast Asia. It is known for its loud human-like whistling song at dawn and dusk. The widely distributed populations show variations in size and plumage with several of them considered as subspecies. Like others in the genus, they feed on the ground, often along streams and in damp places foraging for snails, crabs, fruits and insects.

Taxonomy
The blue whistling thrush was formally described in 1786 by the Austrian naturalist Giovanni Antonio Scopoli under the binomial name Gracula caerulea. The specific epithet is from Latin caeruleus meaning "blue". Scopoli based his account on "Le Merle blue de la Chine" that had been described and illustrated in 1782 by the French naturalist Pierre Sonnerat in his book Voyage aux Indes orientales et a la Chine. The type locality has been restricted to Canton. The blue whistling thrush is now one of nine species placed in the genus Myophonus that was introduced in 1822 by the Dutch zoologist Coenraad Jacob Temminck.

Six subspecies are recognised:
 * M. c. temminckii Vigors, 1831 – mountains of central Asia to central west China and northeast Myanmar
 * M. c. caeruleus (Scopoli, 1786) – central, east China
 * M. c. eugenei Hume, 1873 – central Myanmar to east Thailand, south China and north, central Indochina
 * M. c. crassirostris Robinson, 1910 – southeast Thailand, Cambodia and north, central Malay Peninsula
 * M. c. dichrorhynchus Salvadori, 1879 – south Malay Peninsula and Sumatra
 * M. c. flavirostris (Horsfield, 1821) – Java

Description
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 in length. Weight across the subspecies can range from 136 to 231 g. For comparison, the blue whistling thrush commonly weighs twice as much as an American robin, however the bird is not a true thrush and is found in the old-world flycatcher family. Among standard measurements, the wing chord can measure 15.5 - 20 cm long, the tarsus is 4.5 - 5.5 cm and the bill is 2.9 - 4.6 cm. 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 and 171 g, whereas in India they average 167.5 g and 158.5 g. 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.

Habitat and distribution
It is found along the Tian Shan and Himalayas, in temperate forests and subtropical or tropical moist montane forests. The species ranges across Afghanistan, Bangladesh, Bhutan, Cambodia, China, Hong Kong, India, Indonesia, Kazakhstan, Laos, Macau, Malaysia, Myanmar, Nepal, Tajikistan, Thailand, Tibet, Turkmenistan, Pakistan and Vietnam. They make altitudinal movements in the Himalayas, descending in winter.

Behaviour and ecology
The blue whistling thrush is usually found singly or in pairs. They hop on rocks and move about in quick spurts. They turn over leaves and small stones, cocking their head and checking for movements of prey. When alarmed they spread and droop their tail. They are active well after dusk and during the breeding season (April to August) they tend to sing during the darkness of dawn and dusk when few other birds are calling. The call precedes sunrise the most during November. The alarm call is a shrill kree. The nest is a cup of moss and roots placed in a ledge or hollow beside a stream. The usual clutch consists of 3 to 4 eggs, the pair sometimes raising a second brood. They feed on fruits, earthworms, insects, crabs and snails. Snails and crabs are typically battered on a rock before feeding. In captivity, they have been known to kill and eat mice and in the wild have been recorded preying on small birds.

Perez et al., 2023 find M. caeruleus has an unusually large diameter – 10.4 cm – nest among passerines – the largest among all they surveyed.