The birds which have been sighted include different varieties of ducks, shovellers, herons, and pintails, divisional forest officer of the park Kedar Kumar Swain told IANS.
"More than 25,000 migratory birds have already arrived. The highest concentration of birds so far was found at Satabhaya area of the park," he said.
The birds started arriving in the middle of this month and the number will gradually increase by the second week of December, he added.
Swain said nearly 15 anti-poaching squads, comprising 75 officials and volunteers have been engaged in the park to protect the birds. They are carrying out regular patrol in the park area.
The Bhitarkanika National Park, which is also a wildlife sanctuary, is located 170 km from Bhubaneswar. It is home to over 200 species of birds, including about 100 species of migratory birds.
The sanctuary is also widely known as the world's largest rookery of Olive Ridley sea turtles.
Every year, more than a million migratory birds from places as far as Siberia and Iraq flock to various sites of the state in October-November and return in February-March, often with their fledelings.