(S (S (BASENP (NNS Ornithologists)) (VP (VBP say) (SBAR (S (NP (BASENP (DT each) (NN mating) (NN pair)) (PP (IN of) (BASENP (JJ Ivory-billed) (NNS woodpeckers)))) (VP (VP (VBZ needs) (NP (BASENP (NN three) (NN square) (NNS miles)) (PP (IN of) (BASENP (NN forest))))) (S (VP (TO to) (VP (VB survive))))))))) (PERIOD .))