Studies with captive birds have given us 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. 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, discovered that the lower part of avian brains are similar to ours.
Indications of intelligence in bird species
Birds rely heavily on their eyes for flying and navigation. The brains of many birds must be able to handle tasks differently from other animals. All flying birds must possess a fine level of motor control for in-flight maneuvering and landing.
Most small birds are prey animals. Detecting the movement of predators in their environment is critical. Their eyes are positioned on the sides of their heads to make this easier. They have monocular vision.
Other predatory species like owls are built differently. Their eyes are positioned in the front of their heads so that they can calculate and maneuver a successful strike on a moving target. Owls eyes are so large proportionally, they cannot move them independently. They are stationary inside the skull. That's why they can rotate their heads nearly 360 degrees.
A bird of prey searching for a small rodent from high above the ground must be able to process a huge amount of complex visual information. It helps that they can see in a different color spectrum than humans. According to a video series distributed by PBS.org called "The Life Of Birds" by David Attenborough, new research shows that hawks, for example, can easily see the urine in the grass found around mouse habitats because it glows fluorescently for them. Seeing in a different color spectrum also helps individual birds determine the sex of other members of their species. Light reflects differently off the feathers of males and females. Perceiving this from a distance is obviously an advantage for a bird who is defending his territory.
Some scientists argue that the more social animals are, the more intelligent they seem to be. The human race itself is an example of evidence that would support this conjecture. Both parrots and corvids have shown tendencies towards organized social behaviour. Many corvid species separate into small family groups or "clans" for activities like nesting and territorial defense. The birds will then congregate in massive flocks made up of several different species for migratory purposes. When the migration period is over, they will return to their original family groups. Scientists report that such behaviours indicate intelligence, as they would require the birds to not only recognize and remember their former companions, but also to interpret subtle changes in temperament and appearance.
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.
Use of tools
Like primates, many bird species have taught themselves to use tools.
- 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 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.
- British documentarian David Attenborough, in his mini-series The Life of Birds, captured an innovation the crows in urban Japan had developed. They dropped hard-shelled nuts onto crosswalks. Once they were cracked by cars that ran over them, they were retrieved while the cars were stopped at a red light.
- Striated Herons (Butorides striatus) use bait to catch fish.
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.
Recent studies indicate that they may also have an ability to understand grammatical structures.
A controversial study conducted by Ryan B. Reynolds has suggested budgerigars are able to form simple, meaningful sentences. The evidence consists so far of only audio files, but they have yet to be either proven or disproven. .
Scientists who have studied the mechanisms of bird migration over long distances have shown that while a bird may be instinctively able, and biologically equipped, to make a first flight on its own, adults are less prone to wander off-course than first-year fledglings. The birds were able to learn from experience or remember landmarks for the benefit of future flights.
When a group of birds fly together, they often form a V shape. This creates a slipstream between the birds, making an area of reduced pressure in the middle of the formation. This reduces air-resistance, enabling the flock to travel up to 75% faster than they would individually. The first bird encounters the majority of the air-resistance; as a consequence, the lead bird changes repeatedly as the flock travels. If a bird falls out of formation, two other birds generally leave with that bird to help it return to the flock with a similar formation.
Moreover, birds observe and integrate subtle visual clues to aid in their navigation, including the movement of the sun, visual landmarks, cloud movements, wind direction, and the earth's own magnetic field. Individual birds use different sources of information to navigate and may switch from one source to another while in flight.
Some birds, notably pigeons, have demonstrated the ability to conceptualize. In one study, conducted at Harvard in 1964, it was shown that pigeons have a general concept of "human," which includes male humans and female humans, individual body parts, and the human body from the back, from below, and from above. When shown photographs of all of the above, the pigeons recognized the photos as "human." They also recognized photographs of human beings in "disguise" (i.e, a human in the nude, wearing strange clothes, or shown out of proportion).
Another study conducted with pigeons showed that the birds were able to distinguish between the artworks of different artists. For example, they could tell the difference between a Picasso and a Monet.
Other interesting behaviors showing higher intelligence
In an article published in 1995 by the National Geographic magazine, the macaw project at Tambopata Research Center in the rain forest of Peru studied what the wild birds eat. Since most food items are available only seasonally, researchers discovered that during the dry season, birds are forced to eat seeds that are poisonous. To medicate themselves, hundreds of birds of many species of parrots and macaws congregate at a nearby riverbank at the world's largest known avian clay lick. The clay that they consume helps bind the toxins and prevent sickness in the birds. 
Cormorants used by Chinese fisherman are often rewarded with fish on every seventh fish that they catch. The cormorants learn this pattern and are able to keep count and predict their reward and will wait for it if the fisherman fails to keep count.
Hummingbirds feeding on bushes with flowers are able to remember the spatial distribution of flowers that have nectar and ones that do not and will not revisit bad ones.
Many frugivorous birds have seasonal foraging patterns based on the flowering and fruiting seasons and the locations of fruiting trees in a forest.