It shoud be like this:
→ A small group of birds arrives from South America because before things start evoluting, you need to have birds from somewhere else so they habe something to adapt to.
→ Geographic isolation because they isolate themselves from other birds (since they're in islands) and form new species with new characteristics.
→ Changes is gene pool occur since they have been isolated for a long time and have developed different characteristics that match their environment.
→ Since they have developed different behaviours, the changes in their behaviour prevent them from interbreeding.
Hope it helped,
BioTeacher101
