This issue of 'safe height to fly' always seems to be based on some mythical topographical area where land is at sea level and most GA flies at 1500 - 2000', mil jets at 500 - 700' and birds at 400' ???
Where is this mythical land?
Common sense should prevail - look at the land your flying over and apply it!
Where I fly, a mil jet doing 300kts can be 50' MSD one moment then 1500 MSD 5 seconds later??
GA same: 500' rural, then crossing a large valley: 2500'??
As for birds around here: pick a height, any height , they love to soar off all ridges??? [100' - 5000']
Obviously there are choke points [transit lanes for jets, VRP's for GA and cliffs for birdies], but outside of this, everyone is everywhere...
They most certainly DON'T adhere to specific height bands???