Distribution

From their Afrotropical origins the sparrows now occupy most of Africa and Eurasia. Many species have restricted distributions, but two, the house sparrows (Passer domesticus) and tree sparrows (Passer montanus), occur widely throughout Eurasia and have increased the range of the family through deliberate introductions from the mid-nineteenth century onwards. The house sparrows have now an almost worldwide distribution, absent only from Antarctica and parts of tropical Africa. The tree sparrows have modest populations in North America and Australia, and are now expanding in the southeast Asian archipelagos and some of the Pacific island groups, partly by introduction, but also by natural spread.

The capacity of the house sparrows for rapid range extension is shown by the way they spread from the Urals to the Pacific coast in the nineteenth and twentieth centuries. Following the building of the trans-Siberian railway, they spread more than 3,000 mi (5,500 km) in a little over 100 years. The rates of spread of this and introduced populations have ranged 9-50 mi per year (15-80 km per year).

Most species are sedentary or disperse nomadically outside the breeding season, though a few have a more defined migration. This particularly applies to high latitude and high al titude populations that withdraw to milder regions in the winter. Pale rock sparrows move south to Arabia and northeast Africa in the winter, and the subspecies of the house sparrow Passer d. bactrianus breeds in the Central Asian Republics and Afghanistan and winters in the northern plains of Pakistan. Spanish sparrows (Passer hispaniolensis) breed in a Mediterranean-type climate with a short spring flush, migrating to the northeast for successive broods as suitable conditions wax and wane.

0 0

Post a comment