Sunday, March 27, 2011

Cockatiel : Sexual dimorphism


All wild cockatiel (also known as the Normal Grey Cockatiel) chicks and juveniles are phenotypically female, and virtually indistinguishable from the time of hatching until their first molting. They display horizontal yellow stripes or bars on the ventral surface of their tail feathers, yellow spots on the ventral surface of the primary flight feathers of their wings, a gray colored crest and face, and a dull orange patch on each of their cheeks.
Adult cockatiels are sexually dimorphic, though to a lesser degree than many other avian species. This is only evident after the first molting, typically occurring about six to nine months after hatching: the male loses the white or yellow barring and spots on the underside of his tail feathers and wings. The gray feathers on his cheeks and crest are replaced by bright yellow feathers, while the orange cheek patch becomes brighter and more distinct. The face and crest of the female will typically remain mostly gray, though also with an orange cheek patch. Additionally, the female commonly retains the horizontal barring on the underside of her tail feathers.
The color in cockatiels is derived from two pigments: Melanin (which provides the gray color in the feathers, eyes, beak, and feet), andlipochromes (which provide the yellow color on the face and tail and the orange color of the cheek patch). The gray color of the melanin overrides the yellow and orange of the lipochromes when both are present.
The melanin content decreases in the face of the males as they mature, allowing the yellow and orange lipochromes to be more visible, while an increase in melanin content in the tail causes the disappearance of the horizontal yellow tail bars.
In addition to these visible characteristics, the vocalization of adult males is typically louder and more complex than that of females.

Cockatiel : Taxonomy and etymology


Originally described by Scottish writer and naturalist Robert Kerr in 1793 as Psittacus hollandicus, the Cockatiel (or cockateel) was moved to its own genus, Nymphicus, by Wagler in 1832. Its genus name reflects the experience of one of the earliest groups of Europeans to see the birds in their native habitat; the travelers thought the birds were so beautiful that they named them after mythical nymphs. The specific namehollandicus refers to New Holland, a historic name for Australia.
Its biological relationship had long been argued; it is now classified into a monotypic subfamily Nymphicinae but had sometimes in the past been misclassified among the Platycercinae, the broad-tailed Parakeets. This issue has now been settled with molecular studies. A 1984 study of protein allozymes signalled its closer relationship to cockatoos than to parrots,[3] and Mitochondrial 12S rRNA sequence data[4] places it amongst the Calyptorhynchinae (Dark Cockatoos) subfamily. The unique, Parakeet (meaning LONG-tailed Parrot) morphological feature is a consequence of the decrease in size and accompanying change of ecological niche.
Sequence analysis of intron 7 of the nuclear ?-fibrinogen gene, on the other hand, indicates that it may yet be distinct enough as to warrant recognition of the Nymphicinae rather than inclusion of the genus in the Calyptorhynchinae.[5]
The Cockatiel is now biologically classified as a genuine member of Cacatuidae on account of sharing all of the Cockatoo family's biological features, namely, the erectile crest, a gallbladderpowder down, suppressed cloudy-layer (enabling Lories, Lorikeets (long-tailed Lories), Parakeets and typical Parrot species' display of structural colours such as aquas, blues, greens, purples and turquoises), and facial feathers covering the sides of the beak, all of which are rarely found outside the Cacatuidae family.