Transitions--words or phrases that help the reader move from one sub-topic to the next. 

Thesis: Sea gull's habits are very annoying to humans. 

I Feeding habits
II Population Problems

Look at the two subtopics at right. 
How might a writer move from one sub-topic to the second? 

Example Transition 1:
However, seagulls are annoying in many ways beyond their feeding habits. For example…

Example Transition 2:
Possibly more annoying than their feeding habits are the problems springing from their population. In some instances…

Example Transition 3:

Other examples of how annoying seagulls are come from problems with their population. In many cases...