I think the Winter Atlas survey have shown this trend quite well. The recent observation is a further extension of range of this species in HK. The same is also true for a few forest species. They are increasing in number and becoming more widespread. Re-forestation in HK has produced a very significant changes in forest birds in the last 20 years. Dr. HK Kwok has done two studies that span over 10+ years in TPK. The conclusion generally points to the same trend. For the future, I would predict Bay Woodpecker will breed in HK pretty soon, and other woodpeckers would become more common.
HF Cheung