question: When birds fly together in large groups, how do they all know which direction to turn in unison?
comment: They don't. Birds' movement in large flocks is actually something talked about in a series of mathematical principles called Chaos Theory. The idea is that you can make things *appear* orderly even when they are in chaos (like having 20k birds all independently flying in a group.) Instead of one big piece of organization, the birds all use a simple set of rules to follow: if the bird in front of me moves left, also move left. If the birds to my side change direction, also change direction. Is there a predator? If so, stay in the flock. Using a series of simple rules like this, you get a lot of "order" out of the chaos. It's the same for schools of fish, or herds of elk.
passages: 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.
   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.
   Section::::Studies.:Social behavior.
  
  Social life has been considered to be a driving force for the evolution of intelligence. Many birds have social organizations, and loose aggregations are common. Many corvid species separate into small family groups (or "clans") for activities such as nesting and territorial defense. The birds then congregate in massive flocks made up of several different species for migratory purposes. Some birds use teamwork while hunting. Predatory birds hunting in pairs have been observed using a "bait and switch" technique, whereby one bird will distract the prey while the other swoops in for the kill.
   Keas ("Nestor notabilis"), parrots native to New Zealand, are a distant relative of the grey parrot. They live in complex social groups and do well on cognitive tests. Heaney, Gray, and Taylor gave four captive keas a series of cooperative loose-string tasks. After solo training and shaping with string ends increasingly further apart, two birds were released simultaneously in a joint loose-string task. Both pairs did very well, one pair failing only 5 in 60 trials. Shaping was then used in a delay task, with the partner released after one second, then two, and gradually up to 25 seconds later than the first bird.
   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.
   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 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.
   In the Denmark, there is a biannual phenomenon known as "sort sol" (Danish for "black sun"). This is when flocks of European starlings gather in vast numbers, creating complex shapes against the sky during the spring. It is during this time spent in Denmark that the European starlings spend time gathering food and resting as part of their migration journey. By being in groups this large the European starlings are able to decrease their risk of predation by hawks.
   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
   There are exceptions to fixed action pattern rules. For example, male blond ring doves isolated from their own species will resort to courting a pigeon, then a human's hand, and finally expressing courtship activity alone in their box if they are left alone for a long period of time.
  
  Section::::Exploitation.
   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.
   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.
   Possible improvements:
  
  BULLET::::- bin-lattice spatial subdivision. Entire area the flock can move in is divided into a large number of bins. Each bin stores which birds it contains. Each time a bird moves from one bin to another, lattice has to be updated.
  
  BULLET::::- Example: 2D(3D) grid in a 2D(3D) flocking simulation.
  
  BULLET::::- Complexity: formula_2, k is number of surrounding bins to consider; just when bird's bin is found in formula_3
  
  Lee Spector, Jon Klein, Chris Perry and Mark Feinstein studied the emergence of collective behavior in evolutionary computation systems.
   Aviary experiments conducted with captive flocks of scaly-breasted munia have tested whether producers and scroungers reach the predicted stable equilibrium frequency (see Evolutionarily stable strategy) when individuals are free to choose either behavior. The numbers choosing either producers and scrounger strategies have been shown to converge on stable frequencies while demonstrating that variation in tactics arise through frequency dependent pay-offs from the choice of different feeding strategies.
   Social behavior requires individual identification, and most birds appear to be capable of recognizing mates, siblings and young. Other behaviors such as play and cooperative breeding are also considered indicators of intelligence.
  
  Crows appear to be able to remember who observed them caching food. They also steal food cached by others.
   Recent studies indicate that some birds may have an ability to memorize "syntactic" patterns of sounds, and that they can be taught to reject the ones determined to be incorrect by the human trainers. These experiments were carried out by combining whistles, rattles, warbles, and high-frequency motifs.
  
  Section::::Studies.:Conceptual abilities.
   Birds communicate with their flockmates through song, calls, and body language. Studies have shown that the intricate territorial songs of some birds must be learned at an early age, and that the memory of the song will serve the bird for the rest of its life. Some bird species are able to communicate in several regional varieties of their songs. For example, the New Zealand saddleback will learn the different song "dialects" of clans of its own species, much as human beings might acquire diverse regional dialects. When a territory-owning male of the species dies, a young male will immediately take his place, singing to prospective mates in the dialect appropriate to the territory he is in. Similarly, around 300 tui songs have been recorded. The greater the competition in the area, it has been suggested, the more likely the birds are to actually create or make their song more complex.
   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.
   Birds learn their songs from those made by other birds. In several examples, birds show highly developed repetition abilities: the Sri Lankan Greater racket-tailed drongo ("Dicrurus paradiseus") copies the calls of predators and the alarm signals of other birds Albert's lyrebird ("Menura alberti") can accurately imitate the satin bowerbird ("Ptilonorhynchus violaceus"),
   Measurements of bird flocking have been made using high-speed cameras, and a computer analysis has been made to test the simple rules of flocking mentioned above. It is found that they generally hold true in the case of bird flocking, but the long range attraction rule (cohesion) applies to the nearest 5-10 neighbors of the flocking bird and is independent of the distance of these neighbors from the bird. In addition, there is an anisotropy with regard to this cohesive tendency, with more cohesion being exhibited towards neighbors to the sides of the bird, rather than in front or behind. This is no doubt due to the field of vision of the flying bird being directed to the sides rather than directly forward or backward.
   Studies of waldrapp ibis show that birds spatially coordinate the phase of wing flapping and show wingtip path coherence when flying in V positions, thus enabling them to maximally utilise the available energy of upwash over the entire flap cycle. In contrast, birds flying in a stream immediately behind another do not have wingtip coherence in their flight pattern and their flapping is out of phase, as compared to birds flying in V patterns, so as to avoid the detrimental effects of the downwash due to the leading bird's flight.
  
  Section::::Adaptations for flight.
   In 2010, Bhattacharya and Vicsek used an SPP model to analyse what is happening here. As a paradigm, they considered how flying birds arrive at a collective decision to make a sudden and synchronised change to land. The birds, such as the starlings in the image on the right, have no decision-making leader, yet the flock know exactly how to land in a unified way. The need for the group to land overrides deviating intentions by individual birds. The particle model found that the collective shift to landing depends on perturbations that apply to the individual birds, such as where the birds are in the flock. It is behaviour that can be compared with the way that sand avalanches, if it is piled up, before the point at which symmetric and carefully placed grains would avalanche, because the fluctuations become increasingly non-linear.
   Visual communication among birds may also involve ritualised displays, which have developed from non-signalling actions such as preening, the adjustments of feather position, pecking, or other behaviour. These displays may signal aggression or submission or may contribute to the formation of pair-bonds. The most elaborate displays occur during courtship, where "dances" are often formed from complex combinations of many possible component movements; males' breeding success may depend on the quality of such displays.
   Visual stimuli are also used in male-male competition. In rock sparrows, elaborate feather ornamentations are the best predictor of dominance in foraging groups. It has been shown, through the use of social network analysis to determine patterns of leader-follower interactions, that individuals with the brightest yellow breast patches showed the most dominance in the foraging group and had the most followers compared to less elaborate individuals.
   A 2013 study that tracked the eye movements of peahens responding to male displays found that they looked in the direction of the upper train of feathers only when at long distances and that they looked only at the lower feathers when males displayed close to them. The rattling of the tail and the shaking of the wings helped in keeping the attention of females.
  
  Section::::Behaviour and ecology.:Breeding.
  
presuppositions: When birds fly together in large groups, they all know which direction to turn in unison. Birds flying in large groups know what direction to turn in unison.
corrections: When birds fly together in large groups, they do not know which direction to turn in unison, but follow what the bird in front of them is doing. Birds do not "know" this, the birds follow a simple set of rules, for ex: if the bird to my side changes direction then I will change direction.
raw_presuppositions: When birds fly together in large groups, they all know which direction to turn in unison. Birds flying in large groups know what direction to turn in unison.
raw_corrections: When birds fly together in large groups, they do not know which direction to turn in unison, but follow what the bird in front of them is doing. Birds do not "know" this, the birds follow a simple set of rules, for ex: if the bird to my side changes direction then I will change direction.