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Species of bird From Wikipedia, the free encyclopedia
The western gerygone (Gerygone fusca) is a small, brownish-grey species of passerine bird, which is found in inland and south-west Australia.[3] It is an arboreal, insectivore of open forest, woodland and dry shrubland.[4] It is not currently threatened with extinction (IUCN: Least Concern).[1]
Western gerygone | |
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Subspecies exsul | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Aves |
Order: | Passeriformes |
Family: | Acanthizidae |
Genus: | Gerygone |
Species: | G. fusca |
Binomial name | |
Gerygone fusca (Gould, 1838) | |
Subspecies[2] | |
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Distribution of the western gerygone: Lighter shaded area represents non-breeding migration. |
The western gerygone is a member of the family Acanthizidae (Thornbills and Allies), which has been split from the family Pardalotidae (Pardalotes).[5]
It is a sister-species to the mangrove gerygone (Gerygone levigaster).[6] The close relationship of this phylogenetic pair is suggested by analyses of both morphological characteristics[7] and genetic loci.[8] Populations of a common ancestor of the two species are thought to have diverged after becoming fragmented by severe aridity during the Pleistocene.[9] These two species are now in secondary contact in the Carpentarian Basin, but occupy very different habitats and do not interbreed.[9]
The common name western gerygone and scientific name Gerygone fusca are recognized by the taxonomies of the International Ornithological Congress,[2] Clement's Checklist,[10] the Handbook of the Birds of the World[11] and Christidis and Boles.[12]
The western gerygone has plain, brownish-grey upperparts, with no prominent wing markings.[3] The underparts are whitish, with variable amounts of grey on the throat and breast.[3] The outer tail-feathers are conspicuously marked, with large, white patches at the base, a broad, blackish, subterminal tail band and white tips.[13]
It is usually found singly or in pairs,[14] in the mid to upper storey of trees and shrubs[4] and is often located by its characteristic, persistent song.[4] It can be very active when foraging.[15]
The western gerygone is similar in appearance to several other Australian gerygones, which don't usually share its habitat.[16] Its plumage can be distinguished from these species by the diagnostic large, white patches at base of its outer tail feathers.[3]
The western gerygone is the most widespread gerygone species and is endemic to Australia.[4] Its three subspecies show subtle differences in plumage and form geographically separate populations:[4]
Nomadic individuals may travel far beyond this species' regular geographic limits.[17]
Gerygone species are largely allopatric.[16] They are usually separated from each other by their geographic distribution, or by their preference for different habitats.[16] As it is the only gerygone of the Australian interior, the western gerygone does not overlap geographically with other gerygones throughout most of its range.[3]
There are two island populations.[9] Both are near Perth in Western Australia.[9] Rottnest Island was colonized by the western gerygone in the 1950s.[18] It was first observed on the island in 1955 and rapidly spread into all suitable habitat.[19] On nearby Garden Island, which is closer to the Australian mainland, the species has been present since European records began.[9]
The western gerygone occupies a wide range of wooded habitats.[9] These vary from open sclerophyll forests, dominated by a broad array of eucalyptus species, to sparse mallee and mulga shrublands.[9] It is often found along watercourses.[9] In elevated regions, it only occurs below 850 meters.[4]
Different populations of the western gerygone show different patterns of movement.[9] Those in south-western Western Australia are partial migrants.[9] They breed only in the south-west, but some individuals migrate inland or northwards during winter.[9] Populations in the Carpentarian Basin and on the Eyre Peninsula are sedentary.[9] Desert populations are partially nomadic, responding to inland rainfall.[9]
The western gerygone is insectivorous.[4] Its foraging techniques include probing into bark, gleaning from foliage, hovering outside foliage and aerial strikes from perches.[16] It may join other small birds in mixed-species feeding flocks.[15]
Breeding usually occurs between September and January, but has been recorded from August to March.[20] Courtship involves intricate chases between pairs.[4] Territories are maintained throughout the breeding season and territorial disputes involve agitated calls.[4] Males display by intensely fluttering their wings and tail, with their bodies tilted horizontally.[20]
The nest is a long, oval-shaped, pendent structure, with a hooded entrance near the top and a 'tail' at the bottom.[20] Both sexes build the nest.[20]
The clutch size is 2 or 3 eggs, (rarely 4).[4] The incubation period lasts 10–12 days, and only the female incubates.[20] The nestling period lasts 10–13 days, and both parents feed the nestlings.[20] Fledglings are fed by their parents for up to 15 days, until independence.[4]
The western gerygone's song is an irregular series of clear, high-pitched whistles, with a meandering melody.[3] Each note maintains a consistent pitch and there is a distinct change in pitch between notes.[19] Although the song isn't loud in volume, its persistence and distinctive tonal qualities are often recognizable from long distances.[4] Singing birds may turn their head in different directions with each note.[4]
Across different mainland populations, songs are fairly similar.[19] Singing is mostly confined to the breeding season and this species is far less conspicuous when it is not breeding.[4]
A distinct, new song has emerged in the western gerygone population which colonized Rottnest Island in the 1950s.[19] Unlike the mainland song, its notes are delivered in a strictly repeated melody.[19] (See sound files on right for comparison.) In 2003, it was estimated that more than a third of the western gerygones on Rottnest island sang the new song, including some individuals which sang both the new song and the typical mainland song.[19]
The island biogeography of birdsong is of interest to evolutionary biologists because of its relevance to speciation.[21] The novel western gerygone song on Rottnest Island is a notable example of both cultural innovation and cultural transmission by social learning.[19] It has occurred over a rapid period of time in a recently isolated population.[19] Sexual selection could eventually result in the typical, mainland western gerygone song on Rottnest Island being completely replaced with the novel song.[19] If secondary contact is subsequently established with the original, mainland population, breeding birds may no longer respond to each other's songs.[19] Behavioural reproductive isolation is a mechanism of evolutionary divergence.[22]
The western gerygone is common throughout much of its range, especially in Southwest Australia.[13] Extensive clearing of native vegetation in this region has led to a reduction in abundance.[23] Predation of western gerygones by feral cats is thought to be uncommon.[4]
The Australian inland reaches extremely high temperatures in summer.[24] Heat waves in these regions can result in sudden, dramatic, large-scale avian mortality events, with lasting ecological consequences.[24] The frequency of such events is predicted to increase dramatically in coming decades, due to climate change. This poses a threat to Australia's inland birds, potentially including some western gerygone populations.[24]
Despite a declining population trend,[1] the western gerygone's conservation status is categorized as least concern by the IUCN[1] and by most Australian state legislation.[25] This species occupies a wide variety of habitats across a large geographic range,[1] which encompasses numerous protected areas, including large, secure national parks.[26]
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