It's so small an area with such high a density of birds.
为什么形容词high在a 前面呢，还望老师们不吝赐教，感谢！
你的句子不符合规范语法。规范的表达应该是：
It's so small an area with such a high density of birds.
It's so small an area with so high a density of birds.
