Merge the given sentences together to form a new one.
The sun is setting. The birds are singing.
As the sun sets, the birds fill the air with their melodious singing.
Complete the following task based on the instruction and optional input provided.### Instruction:
Merge the given sentences together to form a new one.

### Input:
The sun is setting. The birds are singing.

### Output:
As the sun sets, the birds fill the air with their melodious singing.