What would make birds chirp in the middle of the night

I heard it could see a predator (like a cat, we have lots nearby), or their could be a nest. Is this really the case though or the only reasons?

I'm wondering because for the past week or two, every night (usually at least after 1am) I hear birds chirping loudly outside. It sounds like their right outside my window but they could just be loud and somewhere nearby. It always sounds like the sun is rising even if its only 3/4am. I just haven't experienced this before, at least not for hours straight on and off like it has been. Anyone else know why their chirping at this time?

P.S: As to why I'm usually up at these times, thats not really important :)

It's a number of factors, but I think that its probably mating season. Many times a recent occurrence of a creature, especially at a particular time of day or night, it's mating time. Males are singing songs to attract the ladies, or the ladies are singin' for a man.

Also it's spring, so many birds are returning from the south, depending on where you live. They will signal and guide each other during mass flight or exodus.

To drown out the noises, keep your windows shut at night, and let a small fan blow continuously. The sound of the fan usually stifles unpleasant sounds, and is very hypnotic during sleeping.

There's probably a new nest of baby birds next to your window!

...That or there's a new predator in the neighborhood. Maybe there's a raccoon or something that found the birds and goes there every night looking for dinner. There are many nocturnal predators that would be looking for food at that time.

Because they got scared of their own shadow, formed by the light of moon.