More than two million raptors soared through skies above Panama City, circling and gliding as they made their way across the Central American capital as they complete the last leg of their 600-plus-mile journey from North to South America.

The two-million-plus total tallied Sunday broke the record for most raptors counted in a single day, shattering last year's then all-time high of 900,000. Raptors is a category of that includes most birds of prey -- hawks, eagles, buzzards, kites, vultures, ospreys, falcons and others.

"The official count from Sunday's massive raptor migration is 2,105,060 birds, most of them turkey vultures and Swainson's hawks," George Angehr, a Smithsonian ornithologist, said in a press release. "A large percentage of the world population of Swainson's hawks probably passed through on their way from the Great Plains to Argentina."

Sunday's count brings Panama's migratory total to more than three million raptors. Few places in the world boast such numbers. Only birdwatchers in Mexico and Israel claim to see such massive movements of feathered predators.

Raptors mostly fly over land, where they can conserve energy by floating on the powerful wind currents. As the land narrows along the Isthmus of Panama, the birds are squeezed into a smaller and smaller funnel, making them easy to see and count.

But why so many all at once? Angehr says several days of bad weather can prevent birds from migrating, causing a traffic jam. When weather improves, the bottleneck releases all at once.

"When you get good flying conditions after several days of rain, they take advantage," Angehr told the Smithsonian Tropical Research Institute in Panama. "There must have been at least 100 miles of raptors. There was a river of birds passing all day."