Gilbert's Whistler

Identification

The adult male, which weighs 29.8-32.5 g, possesses a rufous-coloured chin and throat from its third year of life, as does its most likely closest relative, the red-lored whistler. Both males can easily be differentiated by the colour of their lores: black for the Gilbert's and red for the red-lored whistler. The female Gilbert's whistler (23.5-32.2 g) has a pale grey throat and a white ring around the eye; her underparts can be lightly streaked. Both sexes are uniformly brownish-grey, and have a red iris and a black stubby bill (17–18 mm). Juveniles (30.9 g) are darker than adults, with tinges of brown, and have dark streaks on the breast and belly. Immatures are very similar to adult females except for their brown bill and dark brown iris. Care should be taken not to mistake the female and immature Gilbert's whistler for the female golden or western whistlers where they co-exist.<p>At one stage, the Gilbert's whistler was divided into two subspecies: Pachycephala inornata inornata to the east of the Flinders Ranges with greyish white underparts, and Pachycephala inornata gilberti in the west with cinnamon and buff underparts; this variation is now considered clinal.<p>A study undertaken by Onley, Gardner and Symonds (2020) on possible larger appendages in whistlers caused by climate change (Allen's rule) from museum specimens collected between 1915 and 2013, found an increase in the body size of the Gilbert's whistler at higher latitudes, following Bergmann's rule.

Taxonomy

The family Pachycephalidae originated within the Australo-Papuan region. Together with the red-lored whistler and the olive whistler, the Gilbert's whistler is basal to the genus Pachycephala – the typical whistlers. This old monotypic lineage represents a relictual form that was once more widespread.<p>John Gould, who first described this species in 1841, named it after Mr Gilbert who discovered the bird in Western Australia and collected specimens that he handed over to Gould. As for its scientific name – Pachycephala inornata – in Ancient Greek pachys and kephale respectively mean ‘thick’ and ‘head’; several of the members of the genus Pachycephala are indeed called ‘thickheads’, and other common names for the Gilbert's whistler include black-lored Gilbert thickhead, red-throated thickhead, Gilbert's thickhead, or simply thickhead. With ‘inornatus’ meaning ‘plain’ in Latin, the second part of its binominal name is attributed to the Gilbert's whistler's plumage, which is often described in the literature as being plain.<p>There are several entries in the GenBank DNA sequence database for Pachycephala inornata.

Scientific name

Pachycephala inornata

Authority

Gould, 1841

Order

Passeriformes

Family

Pachycephalidae

Genus

Pachycephala

Range and habitat

Migration

Resident species

Behavior

Gilbert's whistlers feed mostly on the ground, as does about half of all declining species of birds in southern Australia. This species also forages in understorey layers. They feed primarily on invertebrates, although fruit and seeds can also form part of its diet.<p>Gilbert's whistlers erect a deep cup nest in a dense shrub, often on top of old babblers’ nests. Both sexes build the nest, incubate two or three, sometimes four eggs over a period of 15 days, and look after the chicks. Young are altricial and nidicolous.

Conservation

Of the four states in which the Gilbert's whistler occurs, this species is listed as vulnerable only in New South Wales under the NSW Biodiversity Conservation Act 2016 based on population decrease in size and distribution. A conservation strategy was developed in 2015 as part of the Saving our Species program with some of the priority management areas including: restoring native vegetation, removing weeds, implementing actions to reduce the impact of noisy miners when deemed necessary, encouraging landholders to implement sensitive grazing practices, strip burning with refuge areas remaining unburnt for 25 years or more, raising public awareness of the importance of large old trees, revegetating, and identifying methods to improve soil quality.<p>The Gilbert's whistler is not listed at national level under the Environment Protection and Biodiversity Conservation Act 1999, and is listed as least concern at international level under the IUCN Red List of Threatened Species 2016.

Population trend

declining