Birds are

Options

A. Poikilothermic
B. Ectothermic
C. Cold blooded
D. Endothermic

Answer

To determine the correct classification of birds based on their thermoregulation, we can analyze the options provided in the question step by step.

### Step 1: Understand the Term "Poikilothermic"
- Poikilothermic organisms, also known as cold-blooded animals, have body temperatures that vary with the environment. They rely on external sources, such as sunlight, to regulate their body temperature.
- **Hint:** Remember that poikilothermic means the body temperature changes with the environment.

### Step 2: Analyze the Ectothermic Classification
- Ectothermic is another term for poikilothermic. It refers to organisms that cannot internally regulate their body temperature and depend on external heat sources.
- Since birds do not fall into this category, this option is incorrect.
- **Hint:** Ectothermic = cold-blooded; think about how birds regulate their temperature.

### Step 3: Consider the Cold-Blooded Option
- The term "cold-blooded" directly refers to animals that are poikilothermic or ectothermic. Since birds are not cold-blooded, this option is also incorrect.
- **Hint:** Cold-blooded animals cannot maintain a constant body temperature; birds can.

### Step 4: Define Endothermic
- Endothermic organisms, or warm-blooded animals, can generate and maintain their body heat internally. This allows them to keep a stable body temperature regardless of external conditions.
- Birds fall into this category as they can produce heat internally and maintain their body temperature.
- **Hint:** Endothermic = warm-blooded; think about how birds can survive in various temperatures.

### Conclusion
Based on the analysis of the definitions and characteristics of each classification, the correct answer is that birds are **endothermic** (warm-blooded) organisms. Therefore, option 4 is the correct answer.

### Final Answer
Birds are **endothermic** (warm-blooded) organisms.