从八月下旬开始，可以听见非常好听和响亮的鸟鸣声。最初，我想一定是云雀在叫吧，不过我错了。这是雄的蓝矶鸫从高处发出的叫声。

十月，我看见了大约十只的蓝矶鸫聚集在一起飞。

Sfox's correction is a very nice one. Very refined and literary. With no intention to offend anyone, I'll still provide you with a more colloquial version of mine.
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蓝矶鸫 Oct 05, 2010

My suggestion:
从八月下旬开始，就(一直)听见非常好听、非常嘹亮的鸟叫声。起初，我想是云雀在叫吧，不过我错了。原来／其实是雄的蓝矶鸫在那显眼的地方叫着。
在十月里，我看见了大概十只左右的蓝矶鸫聚着飞在一起／聚集，然后一起飞翔。
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Notes:
(1)「从......开始，就(一直) V」 is a very common pattern to say "someone has been doing something since ...". If the verb is an action verb (e.g.跑步, 唱歌)，you need to add a 在 to the front of the verb. For a state verb like 听见, a 在 is not needed.

(2) According to your English version, your 在突出地点 is the translation for "at the outstanding point", which means "at the place that is high in position or can be easily seen". If my understanding is correct, then the 颇具特点的 of Sfox's, despite its beauty, is not very appropriate. It actually means "quite characteristic/distinctive".

(3) It's also very common to use 原来 or 其实 after 不过 to make the linking stronger.

(4)汇集 is quite formal; therefore it doesn't fit in well when the rest of the article is not as formal. If gathering and flying happened at the same time, you can refer to the first bit (or the one before the slash). If gathering and flying happened in sequence/one after the other, please refer to the second bit.

蓝矶鸫 Oct 05, 2010

蓝矶鸫 Oct 05, 2010