We went to the same location to observe the behavior of egrets several times, and it shows egrets like the tree showed on the last post.
However, this evening we found that these group of egrets changed their mind. The stay in a new tree, which is around 15 meters east from the old one and full of gree leaves.
Around 5pm, there are only around 5 egrets on the old tree;
Around 6pm, around 10 egrets back. Three of them landed on the new tree, and others to the old one;
Around 6:30pm, more egrets went back and it seems they prefer choosing the old tree. So there are more egrets on the old tree and less in the new tree.
Suddenly, some egrets took off from the old tree and fly to the new one. This process continued until most of the members fly to the new tree.
I think it is the democracy of the egrets and all egrets voted for their roosting site.