My understanding as a mere PPL is that there is a general speed limit of 250 kts below 10,000 to avoid doing too much damage if a bird strike occurs.
I recall seeing a TV programme once where turkeys were blasted at a windscreen by a cannon to demonstrate / validate this.
Have I got this right or has life moved on ?
sometimes correct, often not.
Regulations are not that specfic. More often experience based (equivalent safety).
Gelatin birds work fine in many test cases and by the time you get them up to 200 kts or so the differences between bird makeups aren't all that significant to the outcome to either the object or the target
Thus the 250 kt 4 lb bird test on aircraft structures seem to cover most of the experience base. Go faster or hit bigger and expect more damage. Most risk for large transports is adressed by the redundancy and/or shielding of critical systems against most bird strike.
It's a matter of a combination of ruggedness and avoidance. The avoidance is aided by keeping below 250 kts in high bird activity areas.
In spite of how fast, how high and how big, anything goes, but probabilities are what counts when it comes to beating what mother nature deals up.