The Java Sparrow is thought to be endemic only to Java, Bali, Kangean, and possibly Bawean. A popular cage bird, it has been widely introduced (both intentionally and unintentionally) to many parts of the world. Introductions to China date to the Ming period. In Japan, the Java Sparrow is mentioned in a handbook of Japanese foods and in a dictionary of the Japanese language published in the seventeenth and eighteenth centuries, respectively. In the past, this species was released in Taiwan during religious ceremonies as an offering to the dead.
Early attempts at introducing Java Sparrows to North America and the Hawaiian Is. during the latter half of the nineteenth century were unsuccessful. Sightings were first documented in Florida in the mid-1950s and on O‘ahu I., Hawaiian Archipelago, in 1964. In Florida, this species reached a peak in numbers in 1969 but was extirpated during the following decade. In contrast, the population on O‘ahu I. has undergone explosive growth: from 4 birds documented on the Honolulu Christmas Bird Count (CBC) in 1969 to 1,096 tallied on this same count in 1995. In addition, Java Sparrows have expanded their distribution to the islands of Hawai‘i, Kaua‘i, Maui, and Moloka‘i. On Puerto Rico, it is established in the capital of San Juan.
Java Sparrows live close to humans and build domed nests under eaves of buildings and other artificial structures. They have a wide repertoire of calls. They are sedentary and highly gregarious, often occurring in large flocks that may number more than 200 birds. Unlike most birds, their sexual development is activated, in part, by decreasing day length. In the Hawaiian Is. and Puerto Rico, they breed during fall and continue breeding through winter.
Because this species subsists largely on seeds, it poses a potential threat to agricultural grain crops, in particular rice. As a result, the U.S. Department of Agriculture Code of Federal Regulations prohibits the importation of this species into the United States and its territories. However, many states allow the possession and interstate traffic of captive-bred birds.
The status of the Java Sparrow is somewhat paradoxical. Although common to abundant in most of its introduced ranges, its native population has declined severely during the last 2 decades as a direct result of trapping for the cage bird trade.