What are two variables that can affect the survival rate of birds?

1. Habitat: The availability and quality of habitat can significantly influence bird survival. Factors like habitat loss, fragmentation, pollution, and climate change can adversely affect bird populations. Suitable nesting sites, food resources, and protection from predators are crucial for bird survival.

2. Predators: Predation is a major factor that can impact the survival of birds. Birds are vulnerable to various predators throughout their life cycle, including eggs, nestlings, and adults. Predators such as mammals, reptiles, and other birds can significantly reduce bird populations and influence their distribution and behavior.