Why do black redstarts exhibit migratory restlessness at night for fewer days than common redstarts?

The statistics given has shown that night-migrating birds are driven by autonomous circadian clocks which is made possible  by sunset cues. This timekeeping that is the autonomous circadian clocks system is probably the key factor in the overall control of nocturnal songbird migration.

Blact redstarts are associated with circadian clock. Seasonal melatonin and circadian clock lead to migratory nocturnal restlessness. The birds that exhibit migratory restlessness at night is due to high levels of melatonin at nights because melatonin are high in the night.

Explanation:

Migratory restlessness is the locomotive performance that birds engaged in before migration. It is common in birds with circadian rhythm.

answer: decrease

a limiting factor is the one which decrease the abundance, distribution and causes extinction of the population of species in a ecosystem. here, predators including hawks, owls and snakes are the limiting factor for the population of mexican free tailed bat.   although bats are nocturnal animals as they forge for food at night these predators also may remain active during night which can decrease the population of the mexican free-tailed bats. also, these bats eat only one type of insects that are moths. the food can also be a limiting factor as all 400 members are dependent upon same type of food needs that are moths. the decrease in the moth population can cause decrease in population size of the mexican free-tailed bats.

therefore, the scenarios will most likely to decrease the population size of the mexican free-tailed bats.