Birds are not characterized by

Options

A. Feathers
B. Jaws modified into beak
C. warm blooded
D. only viviparous

Answer

To solve the question "Birds are not characterized by," we will analyze each option provided to determine which characteristic does not apply to birds.

### Step-by-Step Solution:

1. **Analyze the first option: Feathers**
- Feathers are a defining characteristic of birds. All birds possess feathers, which are essential for flight, insulation, and display.
- **Conclusion**: This option is correct as birds are characterized by feathers.

2. **Analyze the second option: Jaws modified into beak**
- Birds have jaws that are modified into beaks. This adaptation is crucial for their feeding habits and varies widely among different bird species.
- **Conclusion**: This option is also correct as birds are characterized by having beaks.

3. **Analyze the third option: Warm-blooded**
- Birds are warm-blooded (endothermic) animals. They can regulate their body temperature independently of the environment, which is a key characteristic of birds.
- **Conclusion**: This option is correct as birds are indeed warm-blooded.

4. **Analyze the fourth option: Viviparous**
- Viviparous animals give birth to live young after the development of the embryo inside the mother's body. Birds, however, are oviparous, meaning they lay eggs and the development of the embryo occurs outside the mother's body.
- **Conclusion**: This option is incorrect as birds are not characterized by being viviparous.

### Final Answer:
Birds are not characterized by **viviparous**.

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