Which longwing is most likely to be found nesting in a deserted crow's nest?

The Merlin is most likely to be found nesting in a deserted crow's nest because it is known for its adaptability in nesting habits. Merlins often utilize abandoned nests of other birds, especially those of crows or smaller predators, as they may need a suitable high vantage point for their young.

In contrast, the Peregrine, Prairie Falcon, and Gyrfalcon typically prefer more traditional nesting sites. Peregrines often nest on cliffs or tall structures, while Prairie Falcons tend to choose ledges and natural cavities in rocky areas. Gyrfalcons usually prefer higher, more remote locations, often nesting in secluded areas far from potential disturbances. Thus, the preference of the Merlin for repurposing existing structures, particularly those suitable for predatory birds, aligns well with the observation of utilizing deserted crow's nests.