One of the most famous events that took place in St. Francis's life is his sermon to a flock of birds. While traveling with some of his companions, he saw a flock of birds of many different species. Upon seeing the birds, St. Francis felt moved to share with them his love of God. Stopping to speak to the birds, he said "My brother and sister birds, you should praise your Creator and always love him: He gave you feathers for clothes, wings to fly and all other things that you need. It is God who made you noble among all creatures, making your home in thin, pure air. Without sowing or reaping, you receive God's guidance and protection"(Catholicism Pure).
After this event, St. Francis began to call upon all animals to sing praise to their Creator.
This first sermon that he preached to birds is portrayed in the realistic style of painting displayed below.
To learn more: https://catholicismpure.wordpress.com/2011/10/04/francis-of-assisi-preaching-to-birds/