Migration encompasses four related concepts: persistent straight movement; relocation of an individual on a greater scale (both spatially and temporally) than its normal daily activities; seasonal to-and-fro movement of a population between two areas; and movement leading to the redistribution of individuals within a population. Migration can be either obligate, meaning individuals must migrate, or facultative, meaning individuals can "choose" to migrate or not. Within a migratory species or even within a single population, often not all individuals migrate. Complete migration is when all individuals migrate, partial migration is when some individuals migrate while others do not, and differential migration is when the difference between migratory and non-migratory individuals is based on age or sex (for example).While most migratory movements occur on an annual cycle, some daily movements are also referred to as migration. Many aquatic animals make a Diel vertical migration, travelling a few hundred meters up and down the water column, while some jellyfish make daily horizontal migrations, traveling a few hundred meters across a lake.Irregular (non-cyclical) migrations such as irruptions can occur under pressure of famine, overpopulation of a locality, or some more obscure influence.Seasonal migration is the movement of various species from one habitat to another during the year. Resource availability changes depending on seasonal fluctuations, which influence migration patterns. Different species also might migrate for reproductive purposes. Pacific salmon is an example of a species migrating to reproduce. Every year pacific salmon travel upstream to mate and then return to the ocean. Temperature is also a driving factor of migration that is dependent on the time of year. Many species, especially birds, migrate to warmer locations during the winter to escape poor environmental conditions.Circadian Migration is where birds utilize circadian rhythm (CR) to regulate migration in both the fall and the spring. In circadian migration clocks of both circadian (daily) and circannual (annual) patterns are utilized to determine the birds’ orientation in both time and space as they migrate from one destination to the next. This type of migration serves as being advantageous in birds that during the winter remain close to the equator and also to monitor the auditory and spatial memory of the birds’ brain to remember an optimal site of migration. These birds also possess timing programs that provide avians with the distance that bird have to travel in order to reach their destination. To regulate the migration patterns of these birds, the mammalian circadian clock is utilized. This clock serves to allow for the avians to determine when the appropriate time is to migrate and which site will allow the birds to regulate their metabolism to see if traveling by either land or water will serve as being most advantageous for these migrating species.Tidal Migration is the use of tides by organisms to move periodically from one habitat to another. This type of migration is often used in order to find food or mates. Tides can carry organisms horizontally and vertically for as little as a few nanometers to even thousands of kilometers. The most common form of tidal migration is to and from Intertidal zone during daily tidal cycles. These zones are often populated by many different species and are nutrient rich. Organisms like crabs, nematodes, small fish, corals, and other species cycle to these areas as the tides rise and fall typically about every twelve hours. The cycle movements are associated with foraging of marine and bird species. Typically, during low tide smaller or younger species will emerge to forage because they can survive in the shallower water and have less chance of being preyed upon. During high tide, larger species can be found due to the deeper water and nutrient upwelling from the tidal movements.
Smith is observing the migrating patterns of different flocks of birds. He is curious as to which type of migration each species of birds follows. In Flock A, all of the birds migrate. In Flock B, some of the birds migrate and some do not. In Flock C, only the younger birds migrate while the older birds do not migrate.
What type of migration does Flock C exhibit, complete, partial, or differential?