Step 1: Understanding the Concept
A niche is the functional role of a species, including its food and where and when it feeds.
Step 2: Birds in the same habitat
Several bird species can live in one habitat, such as a tree, without competing directly.
Step 3: Reason
They avoid competition because they eat different kinds of food or feed in different ways and places. So they differ in niche because of different eating habits.
Final Answer:
Birds of the same habitat differ in niche because they have different eating habits.
\[ \boxed{\text{(C) }\text{have different eating habits.}} \]