Why in winters birds swell their feathers?

Explanation

### Step-by-Step Solution:

1. **Understanding the Problem**: The question asks why birds swell their feathers during winter. This indicates a need to explore the relationship between feather structure, air, and temperature regulation.

2. **Feather Structure**: Birds have feathers that can be fluffed up. When birds swell their feathers, they create more space between the feathers.

3. **Trapping Air**: By fluffing up their feathers, birds trap air in the spaces created. This trapped air acts as an insulating layer.

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