Black squirrels are a melanistic subgroup of squirrels with black coloration on their fur. The phenomenon occurs with several species of squirrels, although it is most frequent with the eastern gray squirrel (Sciurus carolinensis) and the fox squirrel (Sciurus niger). (Wikipedia)
During this time of year, there is usually a small flock of these birds between Second and Third Beach - usually between 8 and 12 of them. Pretty hard to spot though - have to watch for movement amoung the rocks and mussels.