How I see it. In a real fight, say, four people. Unless you sent a bird off rply before the fight occurred, I'd like to think that logically, the fight lasts no more than 10 minutes icly. Which means, people who were birded only arrive way after the fight happened.
Kids that claim to be on patrol, seen it a lot. For combat, when it is already underway and you have messaged someone via bird, you cannot get involved. Only to pick up the pieces. In crp, this all has to do with ic time, to ooc time. Use a system of ooc to rp time so that other parties cannot get involved till much later.