Surely depends on the aeroplane? We have a bird speed restriction of 313kts below 8,000ft in the 757 and 767. Rumours are that speed only applies to one type but is used on both for commonality. It can't be THAT dangerous as there aren't loads of crashes happening because of birdstrikes on aircraft faster than 250 knots below 10,000ft. And why 250 knots? Why not 270 or 210 or 237? It seems convenient that the ATC speed restriction is the same as the "safe bird speed limit"?
Birds are one of many environmental threats to air safety and like all threats the combinations of variables of speed, aircraft type, location of strike, weight of bird all play a part in whether it's going to be a bad day or just another delay or cancellation,
As such there is no on-off light switch to say that you are safe or unsafe. It's all a matter of probabilities of the combinations..
For current part 25 aircraft, the data suggests that we must be safe enough since it has produced millions of hours of safe flying in the bird filled skies. Sure there have been structural penetrations and even some injuries but only a handful of accidents due to structural failure of the aircraft. Thus the current design criteria (jump this high) responsibly have resulted in an aircraft surviving these in-flight strikes in the 150-250 kt range.
But should there be a meaningful statistical change in the encounter ballistics (number of birds larger than 4 lbs and/or higher aircraft speeds) then the results are going to shift to more accidents per million hours. It's only a question of how many zeros, if any, in front of the numerator.
Like any of our environmental related hazards, it’s the balance between product capability and avoidance tactics that produce our "safe enough" results.