The extinction of passenger pigeon was due to

Options

A. a) increased number of predatory birds
B. b) over exploitation by humans
C. c) non-availability of the food
D. d) bird flu virus infection.

Explanation

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks for the reasons behind the extinction of the passenger pigeon, a bird that was once abundant in the USA.

2. **Identifying the Extinction Causes**: The extinction of the passenger pigeon can be attributed to two main factors:
- **Hunting**: Passenger pigeons were hunted extensively for their meat. This overhunting significantly reduced their population.
- **Deforestation**: The destruction of their natural habitat through deforestation further contributed to their decline, as it reduced the areas where they could live and find food.

3. **Evaluating the Options**: The question provides several options to choose from:
- **Option A**: Increase in the number of predatory birds - This is incorrect as it was not a significant factor in their extinction.
- **Option B**: Over exploitation by humans - This is correct, as both hunting and deforestation are forms of human exploitation.
- **Option C**: Non-availability of food - This is incorrect because the primary food source for passenger pigeons, which was insects, was still available.
- **Option D**: Bird flu virus infection - This is also incorrect as there is no evidence that bird flu contributed to their extinction.

4. **Conclusion**: Based on the analysis of the options, the correct answer is that the extinction of the passenger pigeon was due to **over exploitation by humans** (Option B).