What kind of big bird is this seen walking around Taipei?
I am fairly certain that this is a Malayan Night Heron (Gorsachius melanolophus).

Taiwan is listed as one of the countries where the Malayan night heron can be found. Its diet consists of small reptiles, snails, chilopods, arachnids, crabs and insects. This would explain why you have observed it bend down a lot to look for food.

Needless to say you can find more information in the corresponding Wikipedia article.

Here a photo with better resolution:


Photo by: Pete Morris/Birdquest

In addition, here is a link to a video taken in Taiwan. Does this remind you of the bird that you saw?