question: How do birds in a flock know when to change direction?
comment: URL_0 Basically the birds respond to other birds "flanking into them". Essentially you fly normally until you see another bird turning towards you, then you turn too. And if you see something on your side, you turn and other birds will turn with you.
passages: The control of migration, its timing and response are genetically controlled and appear to be a primitive trait that is present even in non-migratory species of birds. The ability to navigate and orient themselves during migration is a much more complex phenomenon that may include both endogenous programs as well as learning.
  
  Section::::Physiology and control.:Timing.
   Recent studies of starling flocks have shown, however, that each bird modifies its position relative to the six or seven animals directly surrounding it, no matter how close or how far away those animals are. Interactions between flocking starlings are thus based on a topological rule rather than a metric rule. It remains to be seen whether the same rule can be applied to other animals. Another recent study, based on an analysis of high speed camera footage of flocks above Rome and assuming minimal behavioural rules, has convincingly simulated a number of aspects of flock behaviour.
  
  Section::::Collective decision making.
   Flocks of birds often exhibit collective detection. One or more birds initially detect the threat, and other birds that did not perceive the threat detect their departure and also respond by fleeing. The departure of multiple birds simultaneously is likely to be a more effective alarm signal than that of a single bird as birds regularly depart flocks for reasons other than predator detection.
   However recent studies of starling flocks have shown that each bird modifies its position, relative to the six or seven animals directly surrounding it, no matter how close or how far away those animals are. Interactions between flocking starlings are thus based on a topological, rather than a metric, rule. It remains to be seen whether this applies to other animals. Another recent study, based on an analysis of high-speed camera footage of flocks above Rome and assuming minimal behavioural rules, has convincingly simulated a number of aspects of flock behaviour.
  
  Section::::Models.:Evolutionary models.
   Many animals travel hundreds or thousands of miles in seasonal migrations or returns to breeding grounds. They may be guided by the sun, the stars, the polarization of light, magnetic cues, olfactory cues, winds, or a combination of these. This extensive area of research is covered in the main article on Animal navigation.
   Olfactory cues may be important in salmon, which are known to return to the exact river where they hatched. Lockley reports experimental evidence that fish such as minnows can accurately tell the difference between the waters of different rivers. Salmon may use their magnetic sense to navigate to within reach of their river, and then use olfaction to identify the river at close range.
  
  Section::::Mechanisms.:Gravity receptors.
  
  GPS tracing studies indicate that gravity anomalies could play a role in homing pigeon navigation.
  
  Section::::Mechanisms.:Other senses.
   Many birds follow strict time schedules in their activities. These are often dependent upon environmental cues. Birds also are sensitive to day length, and this awareness is especially important as a cue for migratory species. The ability to orient themselves during migrations is attributed to birds' superior sensory abilities, rather than to intelligence.
  
  Section::::Studies.:Beat induction.
  
  Research published in 2008 that was conducted with an Eleonora cockatoo named Snowball has shown that birds can identify the beat of man-made music, an ability known as beat induction.
  
  Section::::Studies.:Self awareness.
   BULLET::::- The participants in a flock of birds or a shoal of fish all maintain their relative positions or alter direction simultaneously due to lateral communication.
  
  BULLET::::- Ants, termites and bees coordinate by lateral communication, mediated in the case of ants and termites, for example, by scent trails. The resulting physical structure is an emergent property of the individual entities.
   In a pioneering experiment, Lockley showed that warblers placed in a planetarium showing the night sky oriented themselves towards the south; when the planetarium sky was then very slowly rotated, the birds maintained their orientation with respect to the displayed stars. Lockley observes that to navigate by the stars, birds would need both a "sextant and chronometer": a built-in ability to read patterns of stars and to navigate by them, which also requires an accurate time-of-day clock.
   Some animals use true navigation for their homing. This means in familiar areas they will use landmarks such as roads, rivers or mountains when flying, or islands and other landmarks while swimming. However, this only works in familiar territory. Homing pigeons, for example, will often navigate using familiar landmarks, such as roads. Sea turtles will also use landmarks to orient themselves.
  
  Section::::Magnetic orientation.
   Ravens ("Corvus corax") have been observed to recruit other ravens to large feeding sites, such as to the carcass of an animal. However, at first glance their motivation for recruiting is less obvious, and the specifics of their communication system are more elusive. Still, it has been documented that ravens must have such a system, as their patterns of gathering at sites clearly indicate that they must have been informed of the presence of the resource. It is believed that non-mated ravens call in a group of other non-mated birds to be able to feed and not get chased away by mated territorial pairs of established ravens.
   Homing pigeons use magnetic field information with other navigational cues. Pioneering researcher William Keeton showed that time-shifted homing pigeons could not orient themselves correctly on a clear sunny day, but could do so on an overcast day, suggesting that the birds prefer to rely on the direction of the sun, but switch to using a magnetic field cue when the sun is not visible. This was confirmed by experiments with magnets: the pigeons could not orient correctly on an overcast day when the magnetic field was disrupted.
  
  Section::::Mechanisms.:Olfaction.
   BULLET::::- Dead reckoning, also known as "path integration," is the process of computing one's position by starting from a known location and keeping track of the distances and directions subsequently traveled. Classic experiments have shown that the desert ant keeps track of its position in this way as it wanders for many meters searching for food. Though it travels in a randomly twisted path, it heads straight home when it finds food. However, if the ant is picked up and released some meters to the east, for example, it heads for a location displaced by the same amount to the east of its home nest.
   The migration of this bird is nocturnal and they are able to detect the geomagnetic field of the earth in order to guide themselves to their breeding and overwinter territory. The orientation of the snow bunting during migration is independent of any type of visual cue. Furthermore, studies have shown that only those individuals with adequate energy storage will be able to select seasonally appropriate directions during their migration.
  
  Section::::Behaviour.
  
  Section::::Behaviour.:Diet.
   BULLET::::- Pigeons can remember large numbers of individual images for a long time, e.g. hundreds of images for periods of several years.
  
  All these are capacities that are likely to be found in most mammal and bird species. In addition pigeons have unusual, perhaps unique, abilities to learn routes back to their home from long distances. This homing behaviour is different from that of birds that learn migration routes, which usually occurs over a fixed route at fixed times of the year, whereas homing is more flexible; however similar mechanisms may be involved.
   Experiments with Manx shearwaters showed that when released "under a clear sky" far from their nests, the seabirds first oriented themselves and then flew off in the correct direction. But if the sky was overcast at the time of release, the shearwaters flew around in circles.
  
  Monarch butterflies use the sun as a compass to guide their southwesterly autumn migration from Canada to Mexico.
  
  Section::::Mechanisms.:Orientation by the night sky.
   Visual or auditory signals and their association with food and other rewards have been well studied, and birds have been trained to recognize and distinguish complex shapes. This is probably an important ability that aids their survival..
  
  Section::::Studies.:Spatial and temporal abilities.
   The insectivorous weaver bird "Ploceus bicolor" can also learn to associate four feeding rooms with four feeding times, and it maintains the correct spatio-temporal pattern even when one of the rooms is blocked on test days (the bird then waits for the next feeding time and visits the appropriate room for that time); however, room blocking disrupts the spatio-temporal pattern in the granivorous weaver bird "Euplectes hordaceus", which suggests that time-place learning may be stronger in species for which food in nature is more likely to vary spatio-temporally (as is the case for insects, as opposed to grain).
   For example, in foraging behaviour, red harvester ants ("Pogonomyrmex barbatus") communicate to other ants where food is, how much food there is, and whether or not they should switch tasks to forage based on cuticular hydrocarbon scents and the rate of ant-interaction. By using the combined odors of forager cuticular hydrocarbons and of seeds and interaction rate using brief antennal contact, the colony captures precise information about the current availability of food and thus whether or not they should switch to foraging behaviour "all without being directed by a central controller or even another ant". The rate at which foragers return with seeds sets the rate at which outgoing foragers leave the nest on foraging trips; faster rates of return indicate more food availability and fewer interactions indicate a greater need for foragers. A combination of these two factors, which are solely based on local information from the environment, leads to decisions about switching to the foraging task and ultimately, to achieving the global goal of feeding the colony.
   Section::::Social insects.:Examples.:Honey bees.
  
  Honey bees ("Apis mellifera") also use quorum sensing to make decisions about new nest sites. Large colonies reproduce through a process called swarming, in which the queen leaves the hive with a portion of the workers to form a new nest elsewhere. After leaving the nest, the workers form a swarm that hangs from a branch or overhanging structure. This swarm persists during the decision-making phase until a new nest site is chosen.
   The ability of birds to return to precise locations across vast distances has been known for some time; in an experiment conducted in the 1950s, a Manx shearwater released in Boston in the United States returned to its colony in Skomer, in Wales within 13 days, a distance of . Birds navigate during migration using a variety of methods. For diurnal migrants, the sun is used to navigate by day, and a stellar compass is used at night. Birds that use the sun compensate for the changing position of the sun during the day by the use of an internal clock. Orientation with the stellar compass depends on the position of the constellations surrounding Polaris. These are backed up in some species by their ability to sense the Earth's geomagnetism through specialised photoreceptors.
   introduced a complementary force to the alignment that they call the change of leadership. This steer defines the chance of the bird to become a leader and try to escape.
  
  Hemelrijk and Hildenbrandt
   Section::::Biology.:Distribution and movements.:Navigation.
  
  Many species in the order travel long distances over open water but return to the same nest site each year, raising the question of how they navigate so accurately. The Welsh naturalist Ronald Lockley carried out early research into animal navigation with the Manx shearwaters that nested on the island of Skokholm. In release experiments, a Manx shearwater flew from Boston to Skokholm, a distance of in 12 days.
   In short, the use of a combination of simple cues makes it possible for red harvester ant colonies to make an accurate and rapid adjustment of foraging activity that corresponds to the current availability of food while using positive feedback for regulation of the process: the faster outgoing foragers meet ants returning with seeds, the more ants go out to forage. Ants then continue to use these local cues in finding food, as they use their olfactory senses to pick up pheromone trails laid by other ants and follow the trail in a descending gradient to the food source. Instead of being directed by other ants or being told as to where the food is, ants rely on their closely coupled action and perception systems to collectively complete the global task.
   Birds can also detect slow moving objects. The movement of the sun and the constellations across the sky is imperceptible to humans, but detected by birds. The ability to detect these movements allows migrating birds to properly orient themselves.
  
raw_presuppositions: Birds in a flock know when to change direction.
raw_corrections: They don't know they just follow the bird in front of them.