I have spent only a few days in Hong Kong during visits in 1998, 2005 and 2017.
It isn’t famous for its mammals but Hong Kong Dolphin Watch run trips to see the pink race of Indo-Pacific Hump-backed Dolphin in the harbour and I saw several in January 1999. There are also Finless Porpoises in these waters, though they hang out in a different area to that visited by the dolphin trips. They are reportedly seen sometimes from the south of Hong Kong island but I was told it takes several hours to walk to the best vantage point.
I returned to Hong Kong in August 2017 for a couple of nights. I wasn’t looking for mammals but couldn’t resist trying to see some of the Greater Short-nosed Fruit Bats (Cynopterus sphinx) that are quite common in the city. They roost in tents in Chinese Palms and can apparently be tracked down in many areas including Kowloon and Victoria Parks. I found a couple in Hong Kong Park, right next to my hotel in Central Hong Kong. The bats were roosting in one of the taller Chinese Palms, in a relatively undisturbed area of the busy park.
I am not sure how faithful the bats are to individual roost trees, but this palm was at the back of the miniature “Olympic” amphitheatre in the park. Walk up the steps of the theatre and continue a few metres onto the dirt and look up at the palms on the right hand side. I saw a Pallas’s Squirrel in a palm in the park too.
Feral domestic water buffalo are common in the south of the main island. And, though I have never been there, Kadoorie Farm looks interesting. Pangolins, Ferret Badgers and Short-nosed Fruit Bats (Cynopterus sphinx) are among the creatures reported to live here.
Hong Kong, 2019: Vladimir Dinets, 6 days & 20 species including Leopard Cat, Yellow-bellied Weasel and Humpbacked Dolphins.
Australia & Hong Kong, 2015: Dominique Brugiere, with some information on Humpbacked Dolphin watching in Hong Kong (at the end).
Hong Kong, 2012: Coke Smith’s account of Humpbacked Dolphin watching in the harbour and birding in the Mai Po Wetlands.