Theory on the messages from the doves in the flash forward with "Sarah".

Theory 1: There's been talk of a flood. Noah learns about dry land by sending out a dove that brings back and olive branch. Perhaps on the 7th anniversary of Departure Day, there's either a flood or an apocalyptic situation. Perhaps 99% of the population departs, and there are so few people left that they're spread out and can't find each other. Maybe the messages are a way for people to find each other. Other possibility is that there's been a failure of electronic communications and sending out birds with messages is the only way to communicate. Doesn't make sense why Nora seems to discard the messages as if she doesn't care. Does someone read the messages elsewhere? Has something happened so that the messages are no longer relevant? Are the birds then reused for more messaging purposes?