Those tiny hawks (Kestrals, Sparrow Hawks) should not be underestimated. You should pen up your birds until you havn't seen the kestral for at least 5 days, maybe a week. That hawk will come back every day until all your chicks are gone. Despite valiant attempts from many of my Roos (and my own), hawks have managed to get some of my birds. Even if your Roo were to try to intervene, he won't always be sucessful.