(S (S (SBAR (IN While) (S (BASENP (NNP Bai) (NNP Yun)) (VP (VBZ has) (VP (VP (VBN been) (ADJP (RB relatively) (JJ fertile))) (PP (IN in) (BASENP (NN captivity))))))) (COMMA ,) (S (BASENP (JJ other) (NNS animals)) (VP (VBP have) (VP (VP (VBN had) (BASENP (NN difficulty))) (S (VP (VBG mating))))))) (PERIOD .))