A question from the SLF gallery here: can any evasive action be taken in situations like that, and if yes, is it advisable? As others have shared in this discussion, geese (apparently) stick to their pre-selected heading, so it would fall upon the pilot to prevent a collision. Would the reaction of an A320 to control inputs (it's not a fighter jet, after all) allow it to change its trajectory sufficiently in 3 seconds to avoid a bird strike?
And an answer from the SLF gallery. It probably all depends on how much time you have. I was on a USAir 737 coming from into PHL from ROC about 10 years ago. We had desended through a thin cloud deck, and as soon as we came out of it, the plane rolled violently to the right into an extremely steep bank angle. I was in a left window seat, and saw a string of birds fly by just below the wing. After we leveled off, the pilot came on to apologize and explain that, upon exiting the cloud deck, we were heading right into a large formation of geese...at 9,000 feet. Evidently he had enough time, but at that speed, we were just lucky. I don't think that 3 seconds from the time you spot them, especially a large formation, is enough to change the direction of an aircraft to avoid a large flock. One bird maybe, but I don't know how you react that fast.
Here is another YouTube video showing a bird strike that brought down a jet fighter, with the view being from the cockpit camera. Watch how fast the bird is upon him.
YouTube - F16 bird strike and eject
Not sure how you avoid that.