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Bird intelligence deals with the definition of intelligence and its measurement as it applies to birds. Traditionally, birds have been considered inferior in intelligence to mammals, and derogatory terms such as bird brains have been used colloquially in some cultures.
It is everywhere recognized that birds possess highly complex instinctive endowments and that their intelligence is very limited.—Herrick, 1924
Such perceptions are no longer considered valid. The difficulty of defining or measuring intelligence makes the subject difficult for scientific study. Anatomically, birds have a relatively large brain compared to head size. The visual and auditory senses are well developed in most species, while tactile and olfactory senses are well developed only in a few groups. Locomotion is achieved through flight and use of the legs in most species. The beak and feet are used to manipulate food and other objects. Birds can communicate using visual signals as well as through the use of calls and song. The testing of intelligence is therefore based on studying the responses to sensory stimuli.
Studies of bird intelligence
Bird intelligence has been studied through several attributes and abilities. Many of these studies have been on birds such as quail, domestic fowl and pigeons kept under captive conditions. It has, however, been noted that field studies have been limited, unlike those of the apes. Birds such as the corvids and psittacines have been shown to live social lives, have long developmental periods and large forebrains, and these may be expected to have greater cognitive abilities.
Counting has been considered an ability that shows intelligence. Early bird photographers used hides to take pictures of birds at nest. They noticed that some species are alarmed by human presence and wait for the human to leave the hide before approaching. Some photographers tried a technique to fool the birds by having two people enter the hide and having only one leave it. Many birds failed to see the trick and returned to their nests assuming that the human had left. However, crows were found to be able to keep count and a figure of 7 was found to be the limit of their counting ability.[How to reference and link to summary or text]
Cormorants used by Chinese fishermen that were given every eighth fish as a reward were found to be able to keep count up to eight.
In the 1970s, on the Li River, Pamela Egremont observed fishermen who allowed the birds to eat every eighth fish they caught. Writing in the Biological Journal of the Linnean Society, she reported that, once their quota of seven fish was filled, the birds "stubbornly refuse to move again until their neck ring is loosened. They ignore an order to dive and even resist a rough push or a knock, sitting glum and motionless on their perches." Meanwhile, other birds that had not filled their quotas continued to catch fish as usual. "One is forced to conclude that these highly intelligent birds can count up to seven," she wrote.—Hoh, E. H.
Many birds are also able to detect changes in the number of eggs in their nest and brood parasitic cuckoos are often known to remove one of the host eggs before laying their own.
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.
Spatial and temporal abilities
A common test of intelligence is the detour test. Here a glass barrier between the bird and an item such as food is used in the setup. Most mammals discover that the objective is reached by first going away from the target. Domestic fowl fail on this test. Many corvids were found to readily solve the problem.
Large fruit-eating birds in tropical forests depend on trees which fruit at different times of the year. Many species, such as pigeons and hornbills, have been shown to be able to decide upon foraging areas according to the time of the year. Birds that show food caching behaviour have also shown the ability to recollect the locations of food caches. Nectarivorous birds such as hummingbirds also optimize their foraging by keeping track of the locations of good and bad flowers. Studies of Western Scrub Jays (Aphelocoma californica) also suggests that birds may be able to plan for the future. They cache food according to future needs and risk of not being able to find the food on subsequent days.
Many birds follow strict time schedules in their activities. These are often dependent upon environmental cues. Birds also are sensitive to daylight 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.
Many birds have been shown capable of using tools. The definition of a tool has been debated. Tool use has been defined as
the use of physical objects other than the animal's own body or appendages as a means to extend the physical influence realized by the animal—Jones and Kamil, 1973
By this definition, an Egyptian vulture dropping a bone on a rock would not be using a tool since the rock cannot be seen as an extension of the body. However the use of a rock manipulated using the beak to crack an ostrich egg would qualify the Egyptian vulture as a tool user. Many other species, including parrots, corvids and a range of passerines, have been noted as tool users.
New Caledonian Crows have been observed in the wild to use stick tools with their beaks to extract insects from logs. While young birds in the wild normally learn this technique from elders, a laboratory crow named "Betty" improvised a hooked tool from a wire with no prior experience. The Woodpecker Finch from the Galapagos Islands also uses simple stick tools to assist it in obtaining food. In captivity, a young Cactus Finch learned to imitate this behaviour by watching a woodpecker finch in an adjacent cage. Crows in urban Japan have innovated a technique to crack hard-shelled nuts by dropping them onto crosswalks and letting them be run over and cracked by cars. They then retrieve the cracked nuts when the cars are stopped at the red light. Striated Herons (Butorides striatus) use bait to catch fish.
Learning using rewards to reinforce responses is often used in laboratories to test intelligence. However, the ability of animals to learn by observation and imitation is considered more significant. Crows have been noted for their ability to learn from each other.
At the beginning of the 20th century, scientists argued that the birds had hyper-developed basal ganglia, with tiny mammalian-like telencephalon structures.. Modern studies have refuted this view  Basal ganglia only occupies a small part of the avian brain. Instead, it seems that birds use a different part of their brain, the medio-rostral neostriatum/hyperstriatum ventrale, as the seat of their intelligence, and the brain-to-body size ratio of psittacines and corvines is actually comparable to that of higher primates.
Studies with captive birds have given insight into which birds are the most intelligent. While parrots have the distinction of being able to mimic human speech, studies with the African Grey Parrot have shown that some are able to associate words with their meanings and form simple sentences (see Alex). Along with parrots, the crows, ravens, and jays (family Corvidae) are perhaps the most intelligent of birds. Not surprisingly, research has shown that these species tend to have the largest hyperstriata. Dr. Harvey J. Karten, a neuroscientist at UCSD who has studied the physiology of birds, has discovered that the lower parts of avian brains are similar to those of humans.
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.
Social behaviour requires individual identification, and most birds appear to be capable of recognizing mates, siblings and young. Other behaviours such as play and cooperative breeding are also considered indicators of intelligence.
When crows are caching food, they appear to be sensitive to note who is watching them hide the food. They also steal food cached by others.
In some fairy-wrens such as the Superb and Red-backed, males pick flower petals in colors contrasting with their bright nuptial plumage and present them to others of their species that will acknowledge, inspect and sometimes manipulate the petals. This function seems not linked to sexual or aggressive activity in the short and medium term thereafter, though its function is apparently not aggressive and quite possibly sexual. 
- Main article: Talking birds
While birds have no form of spoken language, they do 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 a variety of dialects. For example, the New Zealand saddleback will learn the different song "dialects" of clans of its own species, much as human beings might learn 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. [How to reference and link to summary or text]
Recent studies indicate that some birds may have an ability to understand grammatical structures.
Evidence that birds can form abstract concepts such as same–different has been proven by Alex, the African grey parrot. Alex was trained to vocally label more than 100 objects of different colours and shapes and which are made from different materials. Alex can also request or refuse these objects ('I want X') and quantify numbers of them.
A study on the Little Green Bee-eater suggested that these birds may be able to see from the point of view of a predator. Such an ability to see from the point of view of another individual has been attributed only to the Great Apes. Such abilities form the basis for empathy.
- Herrick, C. J. 1924 Neurological foundations of animal behaviour. New York: Henry Holt.
- Nathan J. Emery (2006) Cognitive ornithology: the evolution of avian intelligence. Phil. Trans. R. Soc. B (2006) 361, 23–43 
- Hoh, Erling Hoh (1988) Flying fishes of Wucheng - fisherman in China use cormorants to catch fish. Natural History. October, 1988
- Carter, D. E. & Eckerman, D. A. 1975 Symbolic matching by pigeons: rate of learning complex discriminations predicted from simple discriminations. Science 187, 662–664.
- Scott, John P. 1972. Animal Behavior. Univ. of Chicago Press. Chicago, Ill. p. 193.
- Kamil, A., and R. Balda. 1985. Cache recovery and spatial memory in Clark's nutcrackers (Nucifraga columbiana). Journal of Experimental Psychology and Animal Behavioral Processes 11:95-111.
- Bennett, A. T. D. 1993 Spatial memory in a food storing corvid. I. Near tall landmarks are primarily used. J. Comp. Physiol. A 173, 193–207. (doi:10.1007/BF00192978)
- Healy, S. D. & Hurly, T. A. 1995 Spatial memory in rufous hummingbirds (Selasphorus rufus): a field test. Anim. Learn. Behav. 23, 63–68.
- C. R. Raby, D. M. Alexis, A. Dickinson and N. S. Clayton 2007. Planning for the future by western scrub-jays. Nature 445, 919-921 doi:10.1038/nature05575 PDF
- Jones, T. B. & Kamil, A. C. 1973 Tool-making and tool-using in the northern blue jay. Science 180, 1076–1078.
- Crow making tools
- Bugnyar, T. & Kotrschal, K. 2002 Observational learning and the raiding of food caches in ravens, Corvus corax: is it 'tactical' deception? Anim. Behav. 64, 185–195. (doi:10.1006/anbe.2002.3056)
- Edinger, L., (1908) The relations of comparative anatomy to comparative psychology. Journal of Comparative Neurology and psychology 18:437-457
- [Reiner,A. et al, (2005) Organization and Evolution of the Avian Forebrain The_Anatomical_Record_Part_A 287A:1080-1102
- Iwaniuk, A.N. and Nelson, J.E. (2003) Developmental differences are correlated with relative brain size in birds: A comparative analysis. Canadian Journal of Zoology 81: 1913-1928.
- Evolution of the brain
- N.J. Emery and N.S. Clayton, The mentality of crows: convergent evolution of intelligence in corvids and apes, Science 306 (2004), pp. 1903–1907
- Karubian, Jordan & Alvarado, Allison (2003): Testing the function of petal-carrying in the Red-backed Fairy-wren (Malurus melanocephalus). Emu 103(1):87-92 HTML abstract
- Timothy Q. Gentner, Kimberly M. Fenn, Daniel Margoliash & Howard C. Nusbaum (2006) Recursive syntactic pattern learning by songbirds. Nature 440:1204-1207 abstract
- Pepperberg, I. M. 1999 The Alex studies: cognitive and communicative abilities of Grey parrots. Cambridge, MA: Harvard University Press.
- Watve Milind, Thakar J, Kale A, Pitambekar S. Shaikh I Vaze K, Jog M. Paranjape S. 2002. Bee-eaters ( Merops orientalis) respond to what a predator can see. Animal Cognition 5(4):253-9
- An overview of the brain at the Life of Birds website
- The anatomy of a bird brain
- Crow Makes Tool by Bending Wire to Snag Food
- Tool using in birds
- Video of parrot demonstrating tool use
- Birdminds: Exploring Bird Intelligence
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