Every year, monarch butterflies travel thousands of miles from their summer homes in northern states and Canada to wintering spots in Mexico and southern California. In spring, they make the journey back again. However, the butterflies die before they reach their northern homes. New butterflies, hatched from eggs laid by migrating monarchs, complete the journey. A scientist wanted to know how the new butterflies found their way to their northern homes if they had never been there before. Which of the following is not a testable hypothesis about monarch migratory behavior?

Question

1. Monarchs can sense Earth's magnetic field.
2. Monarchs can smell the remains of last season's Monarchs.
3. Monarchs follow the routes that have many milkweed plants.

Answer 1

The hypothesis that is not testable from the options provided is:

2. Monarchs can smell the remains of last season's Monarchs.

This hypothesis is not easily testable because it relies on the assumption that the butterflies can detect the remains of the previous season's butterflies and use that information for navigation. There is no clear method to measure or test this scent detection in a way that would scientifically validate the hypothesis. In contrast, the other options can be tested through experiments and observations that measure the butterflies' ability to sense magnetic fields or their relationship with milkweed plants.