Massachusetts Comprehensive Assessment System (MCAS) Biology Practice Test

How will natural selection most likely affect seed-eating birds during an extended dry period on an island?

1. All birds will equally survive

2. Birds with large beaks will produce more offspring

3. Birds with small beaks will thrive

4. Only birds with unique feather patterns will survive

The correct answer is: Birds with large beaks will produce more offspring

During an extended dry period on an island, the availability of food sources, particularly seeds, can be dramatically affected. In this scenario, natural selection would favor birds with larger beaks. This is because larger beaks are typically better suited for cracking open tough seeds, which may be the predominant food source during a time of drought when softer seeds might be scarce. The birds with large beaks would be able to access and eat the hard seeds more efficiently than those with smaller beaks, allowing them to survive better in conditions where food is limited. As a result, they would likely have a higher survival rate and, consequently, produce more offspring. This increase in reproductive success would lead to a greater proportion of the next generation having the advantageous trait of larger beaks. Other choices do not align with the principles of adaptation and survival in a changing environment. Birds with small beaks would struggle to access food, and unique feather patterns would not directly enhance survival during a dry period related to food scarcity. The statement that all birds will equally survive overlooks the variations in beak size and the specific advantages that those variations confer in this context.