Which is the most abundant species of bird in the world?

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks for the most abundant species of bird in the world. This means we need to identify which bird species has the largest population.

2. **Classifying Birds**: Birds belong to the class Aves. They are characterized by features such as wings, feathers, and pneumatic bones, which are hollow bones that help reduce body weight for flight.

3. **Identifying Abundant Species**: To find the most abundant species, we look for the bird species with the largest estimated population.

4. **Finding the Answer**: The species identified as the most abundant is the **red-billed quelea**. This bird has an estimated population of approximately **1.5 billion** individuals.

5. **Describing the Red-Billed Quelea**: The red-billed quelea is a wild bird that is roughly the size of a sparrow. It has a stout bill adapted for cracking seeds, which is its primary food source.

6. **Conclusion**: Therefore, the most abundant species of bird in the world is the **red-billed quelea**.