Can we watch other wildlife during a birding trip in Sri Lanka, such as leopards, elephants, sloth bears, and small mammals or butterflies and dragonflies?

Yes, you have a great chance to see other wildlife in a birding tour. This mainly depend on the sites you visit and your tour guide. In your tour itinerary, you have to include the right sites for other wildlife. And you have to have a an expert naturalist guide with an overall knowledge of wildlife. Then you can easily achieve your targets.