Which one of the following is considered as the main reason for the extinction of passenger pigeon?

The two major causes of the extinction of the passenger pigeon:

• Overexploitation - Large flocks and communal breeding made the species highly vulnerable to hunting. As the flocks dwindled in size, populations decreased below the threshold necessary to propagate the species. They were hunted and killed on a massive scale for their meat.
• Habitat loss - Another significant reason for its extinction was deforestation.