They may also have crashed (which would be bad). Try running the Birds in debug mode (don't remember the flag, see bird --help) and collecting their exit value.
I used the command bird -c *confFile* -s *socketFile* -D *debugFile*
in the conf file I inserted:
debug protocols all; debug commands 2;
but i didn't see anything in the debug file i setted, (i need to recompile bird with some option?)