Kokila Vrata

Kokila Vrata

Every 20 years, on the full moon day of the intercalary month when it falls in the Hindu month of Asadha

A kokil is a cuckoo, and this day, which honors Sati, the wife of Shiva, is known as Kokila Vrata because Sati is believed to have once been changed into a cuckoo as a punishment.
According to Hindu mythology, Sati's father, Daksha, agreed to her marriage to Shiva only reluctantly. Daksha hosted a religious feast one day and excluded the couple. Sati appeared at the feast anyway, and soon involved her father in a quarrel over his refusal to accept Shiva as his son-in-law. In anger and vengeance Sati leaped into the sacrificial fire where she burned to death. Since this was considered a sin, she returned to life as a cuckoo in order to make reparation.
Hindus observe Kokila Vrata by eating only one meal per day during the month. They fast entirely on the last day of the month. People also may worship a live cuckoo or an image of one.

SOURCES:
HinduRelCustManners-1960, p. 145
HinduRelYr-1921, p. 117