Birds and mammals share one of the following characteristics as a common feature.

Options

A. Pigmented skin
B. Alimentary canal with some modifica- tion
C. Viviparity
D. Warm blooded nature

Answer

To solve the question regarding the common characteristic shared by birds and mammals, we will analyze each option provided.

### Step-by-Step Solution:

1. **Understanding the Options**:
We need to evaluate the four options given to identify which one is a common feature of both birds and mammals.

2. **Option 1: Pigmented Skin**:
- **Analysis**: Mammals have pigmented skin due to pigments like melanin and carotenoids. However, birds do not have pigmented skin; instead, their feathers are pigmented.
- **Conclusion**: This option is incorrect as it does not apply to both groups.

3. **Option 2: Elementary Canal with Some Modification**:
- **Analysis**: The elementary canal refers to the digestive tract. Birds have beaks and a different digestive system compared to mammals, which have mouths. The structure and function of the digestive systems are not the same.
- **Conclusion**: This option is also incorrect.

4. **Option 3: Viviparity**:
- **Analysis**: Viviparity refers to giving birth to live young, which is a characteristic of most mammals. Birds, on the other hand, lay eggs (oviparity).
- **Conclusion**: This option is incorrect as it does not apply to both groups.

5. **Option 4: Warm-Blooded Nature**:
- **Analysis**: Warm-blooded (endothermic) organisms can maintain a constant body temperature independent of the environment. Both birds and mammals are warm-blooded.
- **Conclusion**: This option is correct as it is a common feature shared by both birds and mammals.

### Final Answer:
The correct answer is **Option 4: Warm-blooded nature**.