A similar article with more information about the squirrel migration of 1968: <a href="https://mentalfloss.com/article/94069/great-squirrel-migration-1968" rel="nofollow">https://mentalfloss.com/article/94069/great-squirrel-migrati...</a>. And since the official links seem to be broken, here's someone's copy of the short research paper "The 1968 Squirrel 'Migration' in the Eastern United States":
<a href="http://www.myoutbox.net/flyger.htm" rel="nofollow">http://www.myoutbox.net/flyger.htm</a>. And to be complete, an article about the author of that paper: <a href="https://umdarchives.wordpress.com/2013/10/04/the-great-squirrel-migration-of-1968/" rel="nofollow">https://umdarchives.wordpress.com/2013/10/04/the-great-squir...</a>.