(S (S (S (BASENP (DT The) (JJ southbound) (NN migration)) (VP (VP (VBD was) (ADVP (RB already))) (NP (BASENP (DT the) (JJS smallest)) (PP (IN in) (BASENP (JJ recorded) (NN history)))))) (CONJP (COMMA ,) (CC and)) (S (PP (IN with) (BASENP (DT the) (JJ destructive) (NN winter))) (COMMA ,) (S (NP (BASENP (RB over) (NN half)) (PP (IN of) (NP (BASENP (DT the) (NNS species) (POS ')) (NN population)))) (VP (MD might) (VP (VB have) (VP (VBN been) (VP (VBN killed)))))))) (PERIOD .))