* Communication: Birds may use chirping as a way to communicate with each other, sharing information about food sources, predators, or potential mates.
* Socializing: Birds may also gather in trees as a way to socialize, strengthening bonds with their flock members and reinforcing their sense of community.
* Territory defense: In some cases, birds may gather in trees to defend their territory from other birds or animals.
* Roosting: Birds may also gather in trees at sunset as a way to roost, or rest, for the night.
It is important to note that the specific reasons why birds gather in trees at sunset and chirp loudly may vary depending on the circumstances.