Final answer:
Torpor allows hummingbirds to conserve energy at night due to their high metabolic rate. Songbirds migrate at night because of fewer predators and cooler air.
Step-by-step explanation:
The concept of torpor is a condition where animals lower their metabolic rate and body temperature, conserving energy. For hummingbirds, which have a high metabolic rate due to their fast wing beats and need for constant food, torpor is essential. At night, when they are not foraging, entering a state of torpor helps hummingbirds conserve energy. During migration, songbirds tend to fly at night because there are fewer predators, and the air is cooler, which makes it easier for them to regulate their body temperature and fly over long distances without overheating. This nocturnal migration also helps them avoid the dehydration and overheating that could occur during the day.