It's July in the deserts of Nevada in the western United States. 美国西部内华达州沙漠的七月
the continent of Antarctica is as large as the United States of America. 面积相当于一个美国
and are on their way north to the southern United States. 正向北飞往美国南部
but beneath these rolling desert slopes in the United States 但是在美国这些荒凉起伏的山崖之下
so although this rocky escarpment in the United States is now hundreds of metres above sea level 所以 尽管美国境内的这座石壁 如今矗立在海平面以上几百米高的地方
400,000 greater snow geese flock to the estuaries along the Atlantic coast of the United States 40万只大西洋雪雁成群飞往 美国大西洋海岸的河口地带