Birds (class Aves)
Birds are more conspicuous than many other animals in the natural environment and are generally quite easily observed and recognized by the members of the public. They tend to be easy to catch in large numbers relatively, and many serve ornamental and sentimental purposes. While at the same time many birds are introduced as game, for example Ring-necked Pheasants (Phasianus colchius) and Chukar (Alectoris chukar), the motive of some introductions is based solely on nostalgia --- the occurrence of common garden birds like the Goldfinch (Carduelis carduelis) in New Zealand and the Song Thrush (Turdus philomelos) in Australia have originated from the whimsical wishes of early colonizers to create a familiar environment in their new homeland. Starlings (Sturnus vulgaris) have been reputedly introduced into the New World originally because people wanted to have all the birds mentioned in Shakespeare texts to appear in the novel, uncharted grounds. The magnificent Ostrich (Struthio camelus) has been shipped to Australia for aviculture in order to obtain its meat and feathers.
Example:
|
Name: European Starling
Order: Passeriformes (Songbirds)
Family: Sturnidae (Starlings)
Scientific name: Sturnus vulgaris |
 |
|
The most successful member of the Starling group is undoubtedly a familiar bird throughout its home range and colonized territories. A sparkling bird and mellifluous songster in its own right, the Starling is small (20cm) and glossed purple and green all over, with shining "stars" --- cream feather tips on the fresh plumage after the post-breeding moult, a blue-based yellow bill and pink feet. Rather gregarious, it is usually seen in flocks of up to fifty individuals and huge flocks of 200 are not uncommon in places. They use communal roosts at night and flock even during breeding season.
The natural range of the species stretches from Scandinavia through Europe to the plains of China, where it is less common. It has been widely introduced into North America, where the species proliferated from approximately 100 birds introduced into the Central Park of New York city in the early 1890s, and is now ever spreading in North America, numbering over 200 million birds. They are now recorded from Alaska to Mexico. They show a preference for human-altered habitats, suburban areas and towns near agricultural areas, but do not refrain from establishing in open countryside with suitable roosts and feeding areas nearby.
Starlings nest in cavities in trees, rocks and artificial structures, and will aggressively evict other cavity-nesters such as Woodpeckers (which excavate their own nest holes), Eastern Bluebirds, Tree Swallows, Great Crested Flycatchers and others, whose numbers are reduced due to nest site competition with the Starlings.
Starlings also cause native insects populations to decline and damage crop, as they feed on insects as well as seed grains, reducing the food supply for both insect-eating birds and seedeaters in the area.
|
Name: House Sparrow
Order: Passeriformes (Songbirds)
Family: Passeridae (Sparrows)
Scientific name: Passer domesticus |
 |
|
Perhaps it would do without a description of this familiar bird of the cities. Being sexually dimorphic, the females are nondescript with a pale brow, being mostly sandy brown all over, whilst the males, quite unmistakably patterned, have a small black mask, grizzly head and chestnut markings on the sides of the head, and a back of bold black streaks on the rich background of brown.
In 1852, 100 Sparrows were introduced to the Brooklyn district of New York. By 1874 it has reached West coast cities like San Francisco. Now the Population of House Sparrows in North America may well have exceeded 150 million. They are confined to open agricultural land and gardens where human activities sustain them, and are generally absent from extensive woodlands, deserts, grasslands and wetlands.
As an introduced species dominating the urban areas wherever introduced, it is immensely successful but displaces most other birds in urban settings or within villages in suburban areas, though a certain degree of competition would inevitably be brought about between the native suburban species and the House Sparrow. House Sparrows are grain eating and they are liable to damage crops when allowed to multiply without control, but predators like Hawks tend to keep the Sparrow population in check. 60% of Sparrow diet consists of livestock feed, and most of the remaining from weed seeds. The House Sparrow remains a largely neutral introduced species, with little effect observed on the peripheral wildlife of human inhabitations, as they mainly rely on humans for sustenance and the impact on native species is generally not as malignant as many other Avian species. However, the fact that it likes to nest under roofs, which degrade the appearance of buildings with grassy nesting materials, is a nuisance to humans, with little associated biological impact.
|
Name: Brown-headed Cowbird
Order: Passeriformes (Songbirds)
Family: Icteridae (American Orioles)
Scientific name: Molothrus alter |
 |
|
Brood parasitism is a curious trait of survival exhibited by various members of the Cuckoo family. Some Passerines however, such as the Cowbirds, have recently also developed the proclivity for adopting this breeding strategy, and some species have become obligate brood parasites – they have to rely on hosts for raising their young and have lost nest-building and young-rearing skills.
This bird originated from the plains of the United States and utilizes almost every type of habitat from open woodland to pastures and fields in ranches, and a wide range of intermediate habitats, feeding on the insects that swarmed around the buffalo. As the bird's source of food was constantly on the move, it developed an ingenious reproductive strategy in adaptation to the environment and the ephemeral, unstable food source. It lays its eggs in the nests of other birds, and relies on the surrogate parents to raise its young. This habit is known as brood parasitism.
(Brood parasitism of cowbird)
When cattle herds spread west with the ranchers in the late 19th century, the Brown-headed Cowbird came with them, laying its eggs in the nests of the native species on the way as they became established. When the egg of the cowbird hatches, the hatchling is substantially sturdier than the other offspring and begins to evict them from the nest or compete with them for food, and it tends to hatch a little sooner because of a shorter incubation period, so that the Cowbird chick usually gains an advantage over the nestlings of the host. The parents end up rearing the cowbird young at the expense of their own, leading to a significant negative impact on the reproductive success of native bird species that are parasitized, which amounts to more than 200 native species in North America.
The Cowbird is a good example of a species experiencing the benefits of human-assisted range expansion. Large-scale deforestation, conversion of woodlands into pastures and urbanization have created large tracts of suitable habitats for the Cowbird and it underwent a population increase afterwards that enabled it to spread widely into both the Northeastern States and the Southwest US from the original confined range of the Central Prairies.
|
Name: Red-vented Bulbul
Order: Passeriformes (Songbirds)
Family: Pycnonotidae (Bulbuls)
Scientific name: Pycnonotus cafer |
 |
|
This clamorous, gregarious bird is aptly named as its under tail coverts are brightly coloured red, otherwise very dark with a short crest. Primarily a frugivore, it is considered widely as an agricultural pest as it causes considerable damage to tomatoes, peas and beans. It is not choosy and will take berries, flowers, plant buds, insects and some small reptiles when available. Areas with trees, including gardens, forests and scrublands, agricultural land and urban area are inhabited. It gathers in flocks and communal roosts as many of the successful invasive species do. One further negative impact of the introduction of this species is that it helps other invasive plant species to disperse their seeds, which allows these exotic plants to proliferate and take over the distinctive native flora of these islands.
From its native range in South Asia it has been introduced into many Pacific Islands, where it competes with other bird species for food. Its aggressiveness and generalist feeding habits are key factors to its status as being one of the most prominent Avian NNS known. Red-vented Bulbuls were introduced in ships navigating among the Pacific Islands.
