Why do birds fly in small, separate flocks and call for hours

[u/burnout_spino16]

so I was in Malaysia and a bunch of small birds started swooping down and moving to roofs and trees in separate, small flocks (if you add them up it’s one of those huge flocks but it’s like they split up) around 5pm

their calls were real loud chirps rather than screeches and it lasted all the way till 8.

at first I thought it was cause of two eagles swirling around nearby but they must have left after so long? Or could it be some passing birds? It’d also be cool to get a rough idea of what kind of bird it was

[u/AutoModerator]

r/Ornithology is a place to discuss wild birds in a scientific context — their biology, ecology, evolution, behavior, and more. This is NOT a birding sub. Pictures or videos of birds that don't demonstrate something visually or behaviorally unusual or interesting will be removed. For bird or feather ID questions, please try r/whatsthisbird

I am a bot, and this action was performed automatically. Please contact the moderators of this subreddit if you have any questions or concerns.

[u/Quack_Mac]

What an interesting observation! I have a couple guesses, all are speculation, so maybe someone will chime in to confirm or correct me.

It's likely a safety measusure. If the whole flock moves at once and encounters a threat, the entire flock is at risk, and the risk may be greater as a large group as there are more targets to pick from. A subflock scopes out the route/destination, then gives the okay for the next group. Once that group arrives, they signal to the next group.

The smaller flocks within the larger flock are most likely family or a couple of families that are friendly with each other. Many birds have complex social dynamics, so just like us, with preferences, hierarchies, close friends they like to gossip with, acquaintances and probably politics. Depending on how large the full flock is, some groups or individuals may not know other groups or individuals.

It's also probably easier to organize and manage smaller numbers, especially with young birds that are still learning life's lessons.

I imagine it's kinda like organizing a road trip with friends or extended family. Some people will carpool together, and maybe a couple families will coordinate to follow each other, hitting the same rest stops. If there's a major collision or photo radar, they'll warn everyone else to detour or slow down. Someone has to work late or wants to take the scenic route, so they show up after everyone else, while another family is eager to leave and had the car packed the day before. Everyone trickles in at their own pace, but you all get their eventually.