The Mudumalai Sanctuary is famous for tigers. This means that option 1 is the correct answer. Tigers are a major attraction in the sanctuary, and they are one of the key reasons why people visit the area. Option 2, bison, might be found in the sanctuary as well, but they are not the main highlight. Option 3, birds, is not the primary focus of the sanctuary either, although there may be a variety of bird species present. Option 4, elephants, could also be found in Mudumalai Sanctuary, but they are not the most famous or sought-after animals in the area. Therefore, the correct answer remains option 1 - tigers.