Sen, I didnt comment immediately coz i decided to look up bird flight formations and find an explanation for the straight formation.
While I didnt spend too much time on it, I found out that it is the heavier birds that do these column formations.
A 'kadi' joke from someone I know - fresh and hot from the grill..."Why do birds fly in a slanting line?" "Coz they want privacy...so that one bird cannot see the other to it's left or right!" :)) Super kadi eh! ;-P
Jo - ha haa...the birds are clever see...they are one behind the other AND at a slight angle - so no one on either side as well as no one at the back or front!