thank u for replying my question
i have checked the CHINA BIRD REPORT. there is no record of the Northern in south China.
and the Asian's records can explain the house martins' distribution in Guangdong better.
however, we mainland birder are very curious about why can't we record the Northern house martin as they breed in northern area and spend winter in southeast asia according to the wild guide to the birds of China
and, i think another characteristic to distinguish these two house martins is their tail forks.
here is another pic also taken in Haifeng
u can see the fork of tail is very shallow, not deep like the Northern house martin according to the wild guide illustrated
so i want to know what the martin u saw looked like
thank u again!