This is an iconic image in Franciscanism, but a modern audience might wonder why. After all, there doesn't seem a lot of point in preaching the Christian message to a flock of birds.
The first thing to consider is the Biblical context: this is Mark Ch 16 v 15: Go ye into all the world, and preach the gospel to every creature.
The second consideration is just how revolutionary the preaching of the mendicant orders was in medieval times. At that time, very little preaching took place in parish churches; the clergy were simply not trained to do it. Preaching took place in cathedrals and monasteries. It was in Latin and dealt with abstruse theological issues. Christ's instruction in Mark's gospel was not happening. The Franciscan preacher delivered the Christian message in language easily understood, often in the open air. The message could then spread far and wide, as fast as the flight of birds.
Here's how Bonaventure describes the event:
'He came to a spot where a large flock of birds of
various kinds had come together. When God’s saint saw them, he quickly
ran to the spot and greeted them as if they were endowed with reason. He
went right up to them and urged them to listen to the word of God,
saying, ‘Oh birds, my brothers and sisters, you have a great obligation
to praise your Creator, who clothed you in feathers and gave you wings
to fly with, provided you with pure air and cares for you without any
worry on your part.
He went through their midst with amazing fervour of
spirit, brushing against them with his tunic. Yet none of them moved
from the spot until the man of God made the sign of the cross and gave
them permission to leave; then they all flew away together. His
companions waiting on the road saw all these things. When he returned to
them, that pure and simple man began to accuse himself of negligence
because he had not preached to the birds before.’
The Louvre panel has many similarities with the Assisi fresco,
particularly that image of the astonished friar behind Francis. It is
particularly good at illustrating the many kinds of birds Francis spoke
to: I'll leave it to more skilled ornithologists to identify the various
species. As with the other images on the panel, this one underlines
the importance of the Franciscan movement.
Upper Church, Assisi
Stigmatization Panel, Louvre
Here are two earlier, though connected images of this scene. On the left below is the fresco from the lower church in Assisi. On the right is the scene from the altarpiece by Coppo di Marcovaldo, now in the Bardi chapel.
Master of St Francis.
Lower Church, Assisi
Coppo di Marcovaldo, c1240-1245