Northern Mockingbird is one of three species of mimic thrushes regularly found around New York City. Mockingbirds are a pugnacious species and will vigorously defend their territory against any perceived threat. I've witnessed, on many occasions, one of these robin-sized gray birds attempting to drive off a Red-tailed Hawk by repeatedly hitting it on the back of the head. Look for these birds in winter safeguarding their claimed fruiting tree, shrub or vine. This individual was in the vicinity of a stand of Yew trees.