Bird keep routes from older bird process

Hello, Sorry for my english, I hope you will understand me. I'm using "Bird" for his OSPF implementation and I have a technical question. I need to keep the routes learned from OSPF after any "Bird" stop or crashes. This can be done with the "persist" option into the kernel configuration block in the bird.conf file. But when I start "Bird" after a stop or a crash of the service, all routes was forgotten. It is possible to tell "Bird" to not erase kernel routes from older "Bird" process? Thanks in advance -- Antoine Habran https://doc.habran.eu