The story of Common Ravens in the east is quite interesting.  During 
colonial days I think they were common (pun intended) around human 
settlements, but by 1900 they had disappeared over most of their eastern 
range.  I not sure of the causes but I suspect that habitat alteration and 
human predation had a lot to do with it.  The remaining populations were in 
remote areas e.g. mountains away from humans. Recently they have began to 
expand into their former range and into more contact with people.
           In all the years I birded Hughes Hollow in Montgomery County I 
didn't record one until 30 September 2007. Since then I have seen them every 
year, mainly in the fall. In 2009 I only recorded them twice, but this year 
I have recorded them fairly regularly in September and October.  Often I see 
them flying over the Potomac River from the Virginia side. My high count is 
four.
        This is a good place to put in a plug for E-bird www.ebird.org .  If 
everyone entered their records (old and new) here we could easily plot the 
raven's expansion.

Paul Woodward
Fairfax City, VA