Despite their popularity, parrots are difficult pets. While they can be emotionally rewarding, they are also emotionally demanding and many species can be quite loud (Peacocks are often considered loud. Parrots can be much louder, with some cockatoos purportedly peaking at 135 db). Parrots are described as "relentlessly social", and many people buy parrots without understanding them, resulting in many birds being abandoned.
Escaped parrots of several species have proved surprisingly hardy in adapting to conditions in Europe and North America. They sometimes even multiply to the point of becoming a nuisance, or a minor pest and a threat to local ecosystems.
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 (see Alex and N'kisi). Along with crows, ravens, and jays (family Corvidae), parrots are considered the most intelligent of birds. The brain-to body size ratio of psittacines and corvines is actually comparable to that of higher primates.
One argument against the supposed intelligent capabilities of bird species is that birds have a relatively small cerebral cortex, which is the part of the brain considered to be the main area of intelligence in other animals. However, it seems that birds use a different part of their brain, the medio-rostral neostriatum/hyperstriatum ventrale, as the seat of their intelligence.
Not surprisingly, research has shown that these species tend to have the largest hyperstriata, and 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. In Animal Planet's program "Most Extreme Animals: Smartest", parrots were ranked #1 as the world's smartest animals. Not only have parrots demonstrated intelligence through scientific testing of their language using ability, but some species of parrot such as the Kea are also highly skilled at using tools and solving puzzles.
Sound imitation and speech
Many species can imitate human speech or other sounds, and the results of a study by Irene Pepperberg suggest a high learning ability in an African Grey Parrot named Alex. Alex has been trained to use words to identify objects, describe them, count them, and even answer complex questions such as "How many red squares?" with over 80% accuracy (which is more impressive than it sounds, considering that transcribers only need to be able to recognize Alex speaking a word with 90% accuracy before that word can be used in tests.
It's also interesting that he scores higher with unfamiliar objects). A second example is that of N'kisi, another African grey, which has been shown to have a vocabulary of approximately a thousand words and has displayed an ability to invent as well as use words in context and in the correct tense.
Parrots do not have vocal cords, so sound is accomplished by expelling air across the mouth of the bifurcated trachea. Different sounds are produced by changing the depth and shape of trachea. So, talking parrots are really whistling in different variations. Congo African Grey parrots (CAG) are well known for their ability to "talk", which may be caused by more control, or stronger trachea. But that dosen't mean that a cockatiel (cockatiels are not well known for talking ability), could have a greater vocabulary than an African Grey parrot.
Parrots as vulnerable or endangered species
The Convention on the International Trade in Endangered Species (CITES) has made trade, import and export of all wild caught parrot and cockatoo species illegal; highly endangered species are protected on the CITES appendix 1 list, and all the other species are protected on the CITES appendix 2 list of vulnerable species. Habitat loss, enviromental changes and illegal trapping remain risks to wild populations.