Superb Fairywren - Description

Description

The Superb Fairywren is 14 cm (5½ in) long and weighs 8–13 g (0.28–0.46 oz), with males on average slightly larger than females. The average tail length is 5.9 cm (2⅓ in), among the shortest in the genus. Averaging 9 mm (0.4 in) in subspecies cyaneus and 8 mm (0.3 in) in subspecies cyanochlamys, the bill is relatively long, narrow and pointed and wider at the base. Wider than it is deep, the bill is similar in shape to those of other birds that feed by probing for or picking insects off their environs.

Like other fairywrens, the Superb Fairywren is notable for its marked sexual dimorphism, males adopting a highly visible breeding plumage of brilliant iridescent blue contrasting with black and grey-brown. The brightly coloured crown and ear tufts are prominently featured in breeding displays. The breeding male has a bright-blue forehead, ear coverts, mantle and tail, brown wings, and black throat, eye band, breast and bill. Females, immatures, and non-breeding males are a plain fawn colour with a lighter underbelly and a fawn (females and immatures) or dull greyish blue (males) tail. The bill is brown in females and juveniles and black in males after their first winter. Immature males moult into breeding plumage the first breeding season after hatching, though incomplete moulting sometimes leaves residual brownish plumage that takes another year or two to perfect. Both sexes moult in autumn after breeding, with males assuming an eclipse non-breeding plumage. They moult again into nuptial plumage in winter or spring. Breeding males' blue plumage, particularly the ear-coverts, is highly iridescent because of the flattened and twisted surface of the barbules. The blue plumage also reflects ultraviolet light strongly, and so may be even more prominent to other fairywrens, whose colour vision extends into this part of the spectrum.

Vocal communication among Superb Fairywrens is used primarily for communication between birds in a social group and for advertising and mobbing, or defending a territory. The basic, or Type I, song is a 1–4 second high-pitched reel consisting of 10–20 short elements per second; it is sung by both males and females. Males also possess a peculiar song-like Type II vocalization, which is given in response to the calls of predatory birds, commonly Grey Butcherbirds (Cracticus torquatus). The purpose of this behaviour, which does not elicit a response from other nearby wrens, remains unknown. It is not a warning call, but in fact gives away the location of the vocalizing male to the predator. It may serve to announce male fitness, but this is far from certain. Superb Fairywrens' alarm call is a series of brief sharp chits, universally given and understood by small birds in response to predators. Females also emit a purr while incubating. Strangely, the bird appears to also use song as a password for its chicks to give it a chance to avoid cuckoo parasites.