Let's see what happens with other polls. I wish Bernie would sling a little mud here. While he was getting arrested in Civil Rights marches Hillary was campaigning for Goldwater. That's a fact and I don't see why it isn't fair game. At the very least, Bernie should be pointing out that issues most concerning to the black community when you ask them are his life's work.
The Clinton's have built many years of goodwill with the black community. In 2008, before Obama won Iowa, Blacks and Hispanics preferred Hillary. What ended up happening was that Obama won over liberal whites, young voters (like Bernie is now) but Blacks left Hillary in the dust once they saw that Obama had a chance. That really hurt Hillary - and allowed Obama to rack up delegates in states with large AA population.
The same thing is going to happen to Bernie if he doesn't make inroads.
Another interesting dynamic could be since a lot of primaries are proportional, AA populations are in more urban, higher delegate areas, Hillary will be able to rack up more delegates compared to her percentage overall in the state.
One of the reasons why I think she prevails in Iowa is because the delegate selection is proportional - Bernie's areas of concentration are in less delegate rich counties, which will hurt him.