Question: when do purple martins migrate to south america
[{'answer': 'winter', 'provenance': [{'wikipedia_id': '18952673', 'title': 'Purple martin', 'start_paragraph_id': 12, 'start_character': 50, 'end_paragraph_id': 12, 'end_character': 56, 'bleu_score': 1.0, 'section': 'Section::::Description and taxonomy.:Distribution and habitat.\n'}]}, {'provenance': [{'wikipedia_id': '18952673', 'title': 'Purple martin', 'start_paragraph_id': 12, 'start_character': 0, 'end_paragraph_id': 12, 'end_character': 151, 'bleu_score': 0.9271474438253491, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 14213605736765851526}, 'section': 'Section::::Description and taxonomy.:Distribution and habitat.\n'}]}]