As I have said before, I really don't think that the ringing data will be of any use in this discussion. Most of the species being discussed are trapped infrequently (flycatchers are generally caught less often than other species because of their behaviour). For example, there have only ever been 2 Grey-streaked, 3 Dark-sided and 7 Narcissus ringed by our ringing group (note that other ringers are active in HK, and I don't have their data).
More flycatchers were trapped in the 1990s because there was a lot of ringing carried out in shrubland at that time - there is now more emphasis on reedbeds, where of course flycatchers are caught less frequently. Inevitably this means that less individuals are now trapped & ringed than was the case a few years ago.
My concern is that you are looking to answer the question 'are migrants declining?' and if you look at the ringing data then you are inevitably going to answer that with a 'yes', even though the ringing data are actually of no use in addressing the question. It is not simply that the data are 'not perfect', they are actually misleading.
For what it's worth, the two most frequently trapped flycatcher species in our data set (which is not all ringing data for Hong Kong) are Yellow-rumped (total 140 trapped - peak years 1991-94, when 17-23 were trapped each year - also good years in 1996 and 2000) and Mugimaki (total 135 - peak years 1992-97, when 10-26 trapped each year).
