What are the modifications that are observed in birds that help them fly?

Explanation

To answer the question about the modifications observed in birds that help them fly, we can break down the key adaptations as follows:

### Step-by-Step Solution:

1. **Pneumatic Bones**:
- Birds have developed pneumatic (hollow) bones. These bones are lightweight, which reduces the overall weight of the bird's skeleton. This adaptation is crucial as it allows birds to be lighter and more agile in the air.

2. **Modified Forelimbs**:
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