The White-Bellied Blue Robin (Sholicola albiventris) is the other important species of the Sholicola genus. It can be differentiated from the Nilgiri Blue Robin (Sholicola major) on the basis of some physical features (related to the plumage). This is how the IUCN Red List of Threatened Species describes the two (both of which it classifies as ‘Endangered’):

  • White-Bellied Blue Robin: 14 cm. Small, chat-like bird with white supercilium, uniform, dark slaty-blue head, breast and upperside. Whitish centre of abdomen with dark slaty-blue flanks and white undertail-coverts. Song a loud, sustained, sprightly, thrust-like series of short phrases, each consisting of rich slurred whistles and dry buzzy notes, rising and falling several times. Calls reportedly include loud chattering and high whistle.
  • Nilgiri Blue Robin: 14 cm. Small, chat-like bird with uniform, dark slaty-blue head, breast and upperside. Whitish centre of abdomen with rufous flanks and undertail-coverts. Song a short jumble of shrill whistles and harsh notes, combining whistled calls and twangy buzzes, sometimes with mimicry. Calls include a strained, indrawn whistle and harsher rattles.

While both are small, insectivorous birds of the forest undergrowth demonstrating much similarity in form and habits, they vary in terms of genetic make-up and geographical distribution. The Nilgiri Blue Robin (Sholicola major) is found in the forests north of the Palakkad (or Palghat) Gap. The White-Bellied Blue Robin (Sholicola albiventris) is found south of it. The Gap divides the Nilgiris to the north from the Anaimalais to the south.

The Anaimalai Hills give way to the Palani Hills in the east. These two ranges, along with the Yelamalai (Cardamom Hills) to their south, are the chief habitat of the White-Bellied Blue Robin. The Palakkad Gap is the proverbial sea to the two sky islands, the Nilgiri Mountains and the Anaimalai-Palani-Yelamalai Hills. It is nearly 40 km wide and a mere 140 m asl. The climate and vegetation of this thin strip is a formidable deterrent to the residents of the montane forests perched high above in the Western Ghats.

DNA sequencing techniques were utilized to identify the position of the species that were till 2017 categorized under the genus Brachypteryx. It was in this year that a separate genus, Sholicola (seen as basal in a clade including  NiltavaCyornis and Eumyias), was erected to house these mysterious passerines. But there was one final twist to the tale. Researchers found that the Ashambu Hills (also known as the Agasthiyarmalai or Pothigai Hills) harboured a third species, the Ashambu Blue Robin (Sholicola ashambuensis).

Again, it was the sky island effect, with the seven-kilometer wide Sengottai or Shencottah Gap keeping apart the Anaimalai-Palani-Yelamalai Hills (to the north) and the Ashambu Hills (to the south). The biggest clue to the distinct identity of the Ashambu Blue Robin lay forgotten (in the form of a specimen going back to 1903) held in the Trivandrum Museum of Natural History, in the state of Kerala. Further investigation into the bird’s plumage, song pattern and genetic composition confirmed the scientists’ speculations. They had stumbled upon, in the form of the genus Sholicola, an evolutionary kaleidoscope.   

Illustration: The image above, sourced from Wikimedia Commons, is a photograph of the White-Bellied Blue Robin. It was uploaded by Navaneeth Kishore.