Passenger pigeon

The Passenger Pigeon is an extinct species of bird that was once native to Earth's North American continent. It was estimated that there were once millions of pigeons that travelled in huge flocks across the continent.

In 2266, Professor Robert Crater compared the M-113 creatures to the Passenger Pigeon, when millions of them roamed the surface of planet M-113. (TOS novelization: "The Unreal McCoy").