A World of Mass Migration

Based on data from 143 weather radar stations from 2013 to 2017, the Cornell Lab of Ornithology estimates that 4 billion birds will fly from Canada across the northern border of the U.S., with 2.6 billion birds returning across the Canada–U.S. border in the Spring.

Activity across the southern border will be on an even grander scale, with an average of 4.7 billion birds laving the U.S. for Mexico and other points south, and 3.5 billion birds heading north across the U.S. southern border in the Spring.