Durga Puja- the neelkanth bird & the Tyndall effect

The Neelkanth, also known as the Indian Roller, is a bird that is traditionally set free during the Durga Puja festival. Celebrated annually from the 6th day of Sharad Navratri, the festival took place in 2023 from Friday, October 20 through Tuesday, October 24. Lets see how a tradition and scientific experiment converge with the Tyndall effect example .

The Blue Throated One

In Calcutta, the Bengalis purchase a Neelkanth bird before the festival and release it when the Durga idol is immersed in the river. This ritual holds great importance to the community. The name “Neelkanth” itself translates to “The Blue Throated One,” emphasizing the distinguishing characteristic of this Indian Roller bird.

From the Legends

Legend has it that during the immersion of the Durga idol in water, a pair of Neelkanth birds is released to carry a message to Lord Shiva. This message informs Shiva of the goddess’s return to her heavenly abode in Kailash. As a result, the act of releasing these birds during Bijoya Dashami, the auspicious day of Dussehra, is considered significant and is believed to bring good fortune.

The Neelkanth Indian Roller, adorned with a vibrant blue tail and stunning azure wings, holds the prestigious position of being the state bird in three Indian states – Odisha, Telengana, and Karnataka. Its remarkable aerial displays during the mating season have garnered widespread recognition.

In addition to this, the sight of the Roller is considered auspicious by the Kol tribe and the people of Bengal. Moreover, incorporating its feathers into cattle feed is believed to enhance milk production. Hence, the Indian Roller is often referred to as the “milk bird” or “pala-pitta” in Southern India.

C.V. Raman’s link to the bird

C.V. Raman’s remarkable academic achievement was intertwined with the noteworthy role played by the Neelkanth Indian Rolle bird. In the 1930s, Raman’s interest shifted from his primary focus on optics and the color of the sea to the color of bird plumage. While it was widely believed that the vibrant blue hue observed in many birds was a result of the Tyndall effect, Raman became the first to challenge this theory. Through extensive research, he conclusively demonstrated the inadequacy of the Tyndall effect in explaining this phenomenon.

An excerpt on Tyndall effect example – copied from https://www.projectnoah.org/spottings/983649664 below

"The Indian roller (Coracias benghalensis) is a bird of the family Coraciidae, the rollers. It occurs widely from West Asia to the Indian Subcontinent. It is 30–34 cm (12–13 in) long with a wingspan of 65–74 cm (26–29 in) and a weight of 166–176 g (5.9–6.2 oz). The face is rufous-white, the throat and breast pinkish, head and back are brown, with blue on the rump and contrasting light and dark blue on the wings and tail. The bright blue markings on the wing are prominent in flight. The sexes are similar in appearance. Two subspecies are recognised. The Indochinese roller was formerly included as a subspecies. Often seen perched along roadside trees and wires, the Indian roller is common in open grassland and scrub forest habitats, and has adapted well to human-modified landscapes. It mainly feeds on insects, especially beetles. The species is best known for the aerobatic displays of males during the breeding season. Adult males and females form pair bonds and raise the young together. The female lays 3–5 eggs in a cavity or crevice, which is lined with a thin mat of straw or feathers. Several states of India have chosen the species as their state bird. It is listed as a species of least concern on the IUCN Red List. The Indian roller is a bulky and broad-winged bird with a large head and short neck and legs. It has a body length of 30–34 cm (12–13 in) with a wingspan of 65–74 cm (26–29 in) and weighs 166–176 g (5.9–6.2 oz). The bare skin around the eyes is dull orange, the legs and feet are yellow-brown. The bill is tinged with brown at the base. The iris is grey-brown. The plumage on the forehead, chin and lores are pinkish buff, the ear coverts are darker red-brown with pale cream or pinkish streaks, while the throat is a dull wine-red with narrow cream streaks. The crown and nape are a darker dull turquoise. The back and rump are a bright turquoise, and the belly is pale blue. The tail coverts are dark purple-blue with turquoise tips. The middle two tail feathers are greyish blue-olive with black shafts, while the surrounding tail feathers are an intense purple-blue with a broad pale blue band and greenish tinge towards the tips. The flight feathers on the wings have the same purple-blue colour of those on the tail, with a similar pale blue band across the most distal five or six primaries. The underwing coverts and axillary feathers are pale blue, while the upperwing coverts are a dull green-blue. The primary coverts are pale blue with olive or purple-blue tips, and the lesser coverts are purple-blue along the leading edge of the wing. The colours look dull when the bird is perched but become vibrant in flight. Moulting commences anywhere from mid-June to mid-August and concludes between November and the beginning of March. Scan of Indian roller feathers, a primary, two outer secondaries and two tail feathers. 

The blue colours of the flight feathers are structural and are produced by microstructures in the barbs that produce blue through scattering, which C.V. Raman noted in the 1930s as being more complex than can be explained by the Tyndall effect. Studies in 2010 found the feather barbs structured like a channel with rods of β-keratin containing rods of 100 nm (3.9×10−6 in) diameter with airspaces between them of the same width. Adult males and females are similar in appearance and there are no seasonal changes. Juvenile birds are duller, paler and browner in colour, with a dull green crown and dull green-blue belly tinged with buff. The bill is brown with a yellowish base rather than black."