In Spring just before trees leaf out, take a pair of binoculars and a bird identification book into a forest near where you live and look for wood warblers. These colourful birds come in flocks in early Spring to eat insects, especially emerging caterpillars on trees. They come in many different colours. Go looking for colourful groups of these tiny birds.
You might find that certain types only forage in the bottom of the forest, while others are in the tops of trees. Try to figure out what adaptive behaviours caused these birds to differentiate into so many different species. One factor is the environment. Another is a divergence in mate preferences.