Shepherding in Israel
H.V. Morton gives an account of this sort of thing: "Early one morning I saw an extraordinary sight not far from Bethlehem. Two shepherds had evidently spent the night with their flocks in a cave. The sheep were all mixed together and the time had come for the shepherds to go in different directions. One of the shepherds stood some distance from the sheep and began to call. First one, then another, then four or five animals ran towards him; and so on until he had counted his whole flock" (In the Steps of the Master, London 1935, pg. 155). George Adam Smith similarly tells of three or four shepherds separating out their flocks solely by their peculiar calls (The Historical Geography of the Holy Land, London, 1931, pp. 311f).
From a sermon by Michael McCartney, I am the Good Shepherd, 6/3/2010