Workers drilling through a wall of the accounts office inside the 177-year-old La Martiniere school building Monday evening found mud covered remains of mostly small birds.
"We have informed the Archaeological Survey of India and the Zoological Survey of India," school secretary Supriyo Dhar told IANS.
The renovation work began last Saturday and the bird skeletons were discovered Monday evening.
"The skeletons are all intact," Dhar said.
Founded in 1836 by Frenchman Claude Martin, a Major General in the British East India Company's Bengal Army, the institute's buildings were constructed five to seven years prior to its opening.
"We are very excited with the discovery, especially since the school building is older than the date of its founding. It is a part of Claude Martin's legacy," said a teacher.