Outcompeting natives for nest sites
The budgerigar (Melopsittacus undulatus), occassionally called the budgie, is a very small parrot species which is very commonly kept as a pet and has become established in a number of countries.
The budgerigar is natvie to Australia, where it is present throughout much of the interior. 
The budgerigar has become established in much of Florida. It's established range is greatest on, but not restricted to, Florida's western Gulf Coast.  These populations may be falling due to competition with other birds, including another introduced species, the European starling.
The budgerigar has also become established in much of Japan, in the prefectures of Niigati, Ibaraki, Tochigi, Saitama, Tokyo, Chiba, Kanagwa, Yamnashi, Shizouka, Nagano, Aichi, Mie, Shiga, Nara, Wakayama, Kyoto, Osaka, Hyogo, Okayama, Kochi, Oita and Miyazaki. 
The budgerigar has also been introduced to South Africa, New Zealand, Switzerland, the United Kingdom and Puerto Rico but have not become established in these countries. 
Pathways and IntroductionEdit
The budgerigar is extremely popular as a pet and as a result has been sold in many countires.[3/4]
Budgerigars have been present in Florida since at least the 1940s, when they were first seen in the city of Saint Petersburg.
Budgerigars were first brought to Great Britain in 1840. It is likely that escaped or hitchhiking animals travelled on ships from Australia to the UK, although the first sightings in the wild were not until 1970 in Tresco.
Budgerigars may compete with native birds for nest sites in some areas and could be carriers of chlamydiosis, also called parrot fever. 
Control and Removal MethodsEdit
No methods of controlling or removing introduced populations of budgerigars have been made.[3/4]