Which type of falcons is known for not building their own nests?

The correct answer is that true falcons are known for not building their own nests. Instead, they often use the abandoned nests of other birds or nest in cliff faces, trees, or ledges. This behavior is a characteristic of the genus Falco, which includes many species of true falcons. These birds have adapted to take advantage of existing structures for nesting rather than expending energy to build their own.

In contrast, forest falcons and caracaras exhibit different nesting behaviors and may engage in nest-building or utilize materials to create their own nests. The statement that all falcons do not build their own nests is too broad, as it does not apply to every species within the falcon family. Therefore, the distinct characteristic of true falcons regarding nesting is what makes this answer accurate.