Obviously you don't want to kill the birds in their nest - that creates an even
worse problem. Likewise you don't want to drive off the parents until the baby
birds can also leave the nest. People make these mistakes with squirrels in
the attic and then they wind up with dead & decomposing adult squirrels and/or
babies in the attic.
I'd wait until the family of birds are all old enough to exit on their own and
then I'd drive them off by venting something slightly noxious through the vent.
A very slight wiff of tear gas or pepper spray might work. Even steam from
boiling water on the stove might make it uncomfortable enough to make them
leave. The possibilities are endless, but just don't kill them in the
I'd replace the vent door with one which prevents entry. Or remove the old one
and rig a screen on the inside of the vent assembly. In either case, I'd fish
out the nest while the vent door is removed. I'd follow that with a very long
blast of compressed air from the range hood side to attempt to blow out as much
debris as possible.
My son is in his first home. Vent hood ducting runs horizontally
about 15 feet to a trap doored vent on side of house. Birds have
gained access and are now rasing a family. (He swears he has observed
the birds lefting the closure with their beaks.) Ducting in wall and
inaccessible. I know a wire screen will prevent recurrence once they
are out. Any suggestions on how to get them out would be appreciated.