I saw a large flock (about 50) of small Falcons high up the sky in Yingjing, Yunnan on 2nd May this year. I guess they were Amur Falcons. I check the number of records in China according to months. Here they are:
Jan 4
Apr 24
May 51
Jun 36
Jul 28
Aug 32
Sept 39
Oct 65
Nov 9
Dec 3
So late April and May is probably a good time to see their migration.
HF Cheung