Which of the following is not a characteristic of birds ?

Options

A. Lungs with air sacs
B. Pneumatic bone
C. Ectothermic
D. Amniotic eggs

Answer

To determine which of the following is not a characteristic of birds, we will analyze each option provided:

1. **Lungs with air sacs**: Birds possess lungs that are complemented by air sacs. This adaptation allows for efficient respiration, enabling birds to extract oxygen more effectively during both inhalation and exhalation. Since this is indeed a characteristic feature of birds, we will not select this option.

2. **Pneumatic bones**: Birds have pneumatic bones, which are hollow bones that reduce weight without sacrificing strength. This adaptation is crucial for flight, making it a characteristic feature of birds. Therefore, we will not select this option either.

3. **Ectothermic**: Ectothermic organisms cannot regulate their body temperature internally and rely on external environmental conditions. Birds, however, are endothermic, meaning they can regulate their body temperature internally. Thus, this option is not a characteristic feature of birds, making it the correct answer.

4. **Amniotic egg**: Birds lay amniotic eggs, which have a protective membrane (amnion) surrounding the embryo. This feature is also characteristic of birds, as well as reptiles and mammals. Therefore, we will not select this option.

In conclusion, the option that is not a characteristic of birds is **ectothermic**.