Fairy-bluebird

The two fairy-bluebirds are small passerine bird species found in forests and plantations in tropical southern Asia and the Philippines. They are the sole members of the genus Irena and family Irenidae, and are related to the ioras and leafbirds.

These are bulbul-like birds of open forest or thorn scrub, but whereas that group tends to be drab in colouration, fairy-bluebirds are sexually dimorphic, with the males being dark blue in plumage, and the females duller green.

These species eat fruit, especially figs, and maybe some insects. They lay 2-3 eggs in a tree nest.

The call of the Asian Fairy-bluebird is a liquid two note Glue-It.

As the names would suggest, the Asian Fairy-bluebird occurs across southern Asia, and the Philippine Fairy-bluebird in that archipelago.

Taxonomy

The first scientists to examine fairy-bluebirds placed them in the roller genus Coracias, presumably on the strength of the iridescent blue plumage on the back. This was challenged in the 1820s by Thomas Horsfield and Coenraad Temminck, who suggested a relationship instead with the drongos. It was variously placed with the bulbuls and orioles as well. On the basis of the DNA-DNA hybridization studies of Sibley and Alhquist its closest relatives have now been identified as the leafbirds. The leafbirds are sometimes included in the family Irenidae with the fairy-bluebirds, but the time since the apparent divergence suggests that they are better treated as separate families.

Morphology

Fairy-bluebirds are robust birds that resemble Old World orioles in shape and size. Males are larger than females, and the two species weigh between 50-100 g, with some of that variation being caused by sexual differences and some by geographic variation. There are clines in size differences in both species which can be attributed to Bergmann's rule, with the northernmost pouplations being larger on average. Both species have a powerful deep and notched bill used for crushing, with that of the Philippine species being larger. Their feet are small, which suggests that they spend less time climbing in order too feed and more time on the wing.

The plumage of the fairy-bluebirds is exceptional, with the upperparts being deep rich blue. The Asian Fairy-bluebird is sexually dimorphic in its plumage, with the male being much brighter than the female, but the Philippine Fairy-bluebird exibits much less difference and the female is almost as bright as the male. The deep colour is provided by specialised naked feather-tip barbs. Although the fairy-bluebirds are highly visible in sunlight they are much more cryptic in the shade of the forest.

Distribution and habitat

The Asian Fairy-bluebird has a discontinuous distribution from India to Java and Vietnam. In India the species is present in the south west of the country and in the north east. From Burma it has a continuous distribution (in suitable habitat) throughout most of South East Asia, and down into Borneo and Sumatra, as well as on the Andaman Islands. The species has not been reliably recorded on Sri Lanka since the 1870s. The Philippine Fairy-bluebird is found on Luzon, Polillo, Leyte, Samar, Mindanao, Dinagat and Basilan.

The fairy-bluebirds are dependent upon fruit producing forests, but both species seem to exist in a wide range of forests, both evergreen and semi-evergreen. Within forests they are generally found in the canopy.

Behaviour

Pairs or small groups (individuals are seldom seen alone) of fairy-bluebirds forage widely to obtain food. Fruit, particularly figs in the genus Ficus, are the most important item in the diet of fairy-bluebirds. Fairy-bluebirds will generally eat fruit of a certain size, and will crush larger fruits in order to make them manageable. Most food is obtained in the canopy. In addition to fruit berries may be eaten, as well as nectar, although this behaviour has only been reported in birds in India. In contrast to adults, hoeever, insects are the principal component of the diet of nestlings. In the Philippines birds have been observed following troops of macaques, possibly in order to collect flushed insects.