Acclimatization is, “the process of an organism adjusting to chronic change in its environment, often involving temperature, moisture, food, often relating to seasonal climate changes,” and it is relevant in aviculture when you import a bird from overseas.
If you take the step of importing a bird then the first phase is quarantine, however, it is important to note that quarantine marks the start of the acclimatization process, and even after release from quarantine it can take up to two years for a bird to fully acclimatize.
If you are in a climate with cold and frosty winters then you would not be able put an imported tropical bid outside in an aviary unless it is summer. In fact for the first two winters it is advisable to keep the bird inside, and for the third winter and beyond you must ensure adequate shelter is provided in the aviary.
Another part of the acclimatization process is that of introducing a new bird to an aviary shared by other birds. In the first few days you should closely monitor the new bird for signs of distress. The risk of a new bird being bullied is much heightened during the breeding season and you should not introduce a new bird to an established group at this time.
The most famous example of acclimatization of birds, and an illustration of how difficult it can be, dates back to1872 when German immigrant Andrew Erkenbrecher decided to introduce the song birds he had grown up with in his childhood into his adopted city of Cincinnati. In a two year period he imported 4,000 birds of various species: robin redbreast, wagtail, skylark, starling, dunnock, blackbird, goldfinch, nightingale, song thrush, great tit, dutch tit, Hungarian thrush, missel thrush, crossbill, siskin, dipper, corncrake, and sparrows. This came at great expense to Erkenbrecher yet the acclimatization was a total failure and the birds disappeared – the process of releasing the birds one fine May day was inadequate.
When you take on the process it should be far more carefully planned and it will be tailored to the specific species of bird. For example, a Senegal Parrot will need protection from any wet and cold weather, but can be kept in an aviary. That said if you have two Senegals then it is best to keep them separate as they argue. With a Blue Fronted Amazon Parrot you will find that they are noisy in the mornings and evenings so you will want to keep them sheltered at these times. So you can see that acclimatization as a general process must be considered, and also the specific needs of the species you are introducing.