How does the endoskeleton of birds help them to fly?

Explanation

### Step-by-Step Solution:

1. **Understanding Endoskeleton**: The endoskeleton of birds is the internal skeletal structure made up of bones. It provides support and shape to the bird's body.

2. **Pneumatic Bones**: Birds have a special type of bone known as pneumatic bones. These bones are hollow, meaning they do not contain bone marrow.

3. **Lightweight Structure**: The absence of bone marrow in pneumatic bones makes them lighter than the solid bones found in many other animals. This reduction in weight is crucial for flight.

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