A bird is usually not an issue (unless it's huge like a condor or something). The problem is ingesting a whole flock. Turbofans are designed to fling debris (r

A bird is usually not an issue (unless it's huge like a condor or something). The problem is ingesting a whole flock. Turbofans are designed to fling debris (rain, hail, gravel, birds) out to the bypass via centrifugal force. However, too much material (or insufficient thrust) causes the impeller to bog down, so more junk gets sucked into the burn chamber, which can cause a flameout.