Judge Mahesh Sharma told TV channels that "the peahen gets pregnant" only by "swallowing the tears of the peacock".
He made the remark to back his observation that cows should replace the tiger as the national animal because "it's also holy".
Experts have rejected his claims.
Mr Sharma told reporters in the northern Indian city of Jaipur that he believed people revere both peacocks and cows because of their "divine qualities".
He added that he had recommended that the government should immediately declare the cow as the national animal.
But social media users vehemently disagreed.
Experts said there was no merit in Mr Sharma's theories.
"This theory about peacocks drinking tears to breed is an old hoax. They breed like all other birds, by means of sexual copulation," Bikram Grewal, an ornithologist, told The Indian Express newspaper.
Mr Sharma is not alone in demanding national status for cows, considered sacred by India's majority Hindu community.
Many states have actively started enforcing bans on cow slaughter after the Hindu nationalist Bharatiya Janata Party (BJP) formed India's federal government in 2014.
In addition to government bans, several vigilante groups who portray themselves as protectors of cows have also been active in several states.
But Mr Sharma added that his demand was not linked to the ongoing debate about banning cow slaughter in the country.
Social media users are ridiculing a judge after he said the peacock was chosen as India's national bird because "it's considered pious" and follows "life-long celibacy".