"....saw a huge dense flock of birds...."
But, I got real stick from ATC at Amsterdam some 15 years ago for refusing to begin the take off roll when I saw a large flock of geese from right to left just where we would have been lifting off.
"Take off immediately or you will lose your slot". Needless to say, I didn't take off and didn't lose my slot.
A photo I took in northwest Norfolk earlier this week shows a typical flock of Pinkfooted Geese; I posted it on a Bird Forum. You'd want to miss a flock like this:
http://www.birdforum.net/gallery/dat...4-Pinkfeet.jpg