For many people the word “warbler” suggests a dull brownish bird singing a gentle. Trilling song (i.e. warbling) from a concealed perch in dense vegetation. Such unobtrusiveness and drabness of plumage are indeed characteristics of many Old World warblers, but: this large subfamily contains numerous distinctive species. No fewer than 25 of the 56 genera contain only one species, although many of these and other members of the subfamily are of doubtful affinity and some may note true warblers at all. The taxonomic confusion surrounding warblers is highlighted by some of the vernacular names; the Oriole babbler, tit-flycatchers, and tit-weavers areal currently regarded as warblers.
The great majority of species are neither Eurasia nor Africa. The New World warblers have nine primary feathers and are not close relatives of the mainly Old World ‘warblers which have ten primary feathers. However, some species of Old World warblers occur in the New World! There are T 3 species ofgnatwrens and gnatcatchers and 2 kinglets. In addition, the Arctic warbler has extended its breeding range from Siberia into western Alaska, although even these birds return to tithe Old World to winter in southern Asia.
Mainland Australia has only 8 resident species, including the distinctive Spinier bird, and New Zealand has only one, the fern bird. The archipelagoes of the Pacific and Indian Oceans contain a variety of unique warblers. The tiny populations of some of these island endemics make them highly vulnerable to extinction. The Aldabrawarbler, whose population was fewer than birds in 1983, is a good example of this.
Typical warblers are small birds with fine, narrowly pointed hills. Their feet are strong and well-suited for perching. Some (egg Dart-ford warbler) have long tails which counter-balance the body as the birds thread their way through dense foliage, carrying out inspections over and under leaves and twigs in their tireless search for insects.
Warblers’ dependence on insect prey is the main reason why most warblers of high latitudes are strongly migratory. Most north Eurasian warblers winter in Africa or tropical Asia, some performing prodigious journeys. For example, Willow warblers nesting in Siberia travel up to 7 2,000km (7,5oomi) twice a year, to and from sub-Saharan Africa. These long-distance migrants accumulate substantial reserves of fuel, in the form of fat deposits, before their journeys. It is not unusual for them to double their body weight in preparation frothier migration. Those few warblers that remain in cold climates in winter are sometimes badly affected by food shortages in harsh weather. Dart ford warblers in Britain, for example, often suffer large population decreases during severe winters.
Warblers are typically monogamous although instances of polygamy are known for several’ species (egg Sedge warbler). Voice has recently been shown to the important in some species for mate attraction and mate selection, in addition to being a primary means of advertising the positions of territorial boundaries. Male Sedge warblers may cease to sing after pairing and individual Reed warblers with elaborate song repertoires tend to succeed in attract-in females sooner than less accomplished singers.
Some species (egg Citrine warbler) extend their repertoires by mimicking other bird species, for reasons that are not understood. The Marsh warbler has gone further: its song consists entirely of imitations of other species. Each Marsh warbler mimics on average so species, over half of them African birds heard in the warbler’s winter quarters. The voice also plays an important part in distinguishing species.
For example, chiffchaffs and Willow warblers look almost identical but have unmistakably distinct songs. Songs are generally delivered from perches, but warblers of low vegetation often use song flights as a means of broadcasting their songs for long distances. Examples of these include scrub warblers, such as the white-throat, and many of the Cist cola grass warblers, such as the Cloud-scraper.
All warblers seem to be competing for the same basic food: insects. In practice, there is often a high degree of spatial separation which minimizes competition for food between species and between individuals. Species that occur at high densities, notably the temperate-zone ones, are characteristically territorial. Typically the males defend territories against members of their species and sometimes also against members of closely related species.
For example, blackcaps and Garden warblers defend territories against each other as well as against other members of their species. In the first case, the territories of both species are large and supply most of the food of the nest-ting pairs and their broods. In the latter, however, breeding territories are small and perhaps serve mainly to space out nests to make it less profitable for predators to specialize in searching for them.
Territorial behavior is not confined to the breeding season nor is it necessarily always directed at other warblers. For example, blackcaps using bird tables or taking nectar from a particular bush will drive off species of similar or smaller size that try to feed there too.
Some warblers achieve ecological segregation by other means. Vertical separation
sometimes occurs: for example, the Long-billed crumbed forages lower down in the vegetation, where its range overlaps with that of a close relative, the Red-faced crumbed, than it does elsewhere. Sometimes where species co-occur there is dietary specialization. For example, the nestling diets of Reed and Great reed warblers tend to differ where the two species are nesting in the same reed bed.
But not where they occur apart from each other. Large warbler species are often found to coexist peacefully with smaller ones. Ecological segregation here may be due to the specialization of the prey of different sizes and to differences in foraging behavior. For example, blackcap and chaff-chaff breeding territories often overlap in Europe since the two species share the same habitat, i.e. deciduous woodland. Blackcaps take fewer tiny insects than do the smaller chiffchaffs and, in addition, blackcaps feed to a large extent on settled insects whereas chiffchaffs often fly catch. Or hover to take insects from the extremities of leaves and twigs where they may be inaccessible to blackcaps.
The log runners are a group of secretive birds, more often heard than seen. Most species are consequently rather poorly known indeed wedgebill was recently split into two species based on calls: the Chirruping wedgebillcalls “tootsie-cheer” and the Chiming wedge-bill “did-you-get-drunk.” The wedge-bills and whip birds perform duets, the male easternwhipbird giving a characteristic whipcrack to which the female replies “cher, cher.”
The name quail-thrush describes the genus Cinclosoma well, as they are thrush-like in proportions and plumage yet are ground-dwelling and eat seeds and insects. They mostly live in desert or eucalypt or acacia woodlands in Australia whereas most of the other log runners occupy the understory of rainforest in eastern Australia and NewGuinea, where they are chiefly insectivorous. Although most species are cryptically colored the Blue jewel-babbler male is blue and white. Most are dumpy birds with rather long tails; they have strong feet, which are used for digging. Logrunnersoften digs in areas from which Brush turkeys have removed the leaf litter for their mounds.
Logrunners may engage in noisy territorial battles in the breeding season, and perhaps most species are monogamous and territorial. Nests of dry sticks, bark, roots, and grass are placed in thick foliage or on the ground, in winter and spring, but occasionally in the fall. Though quail thrushes mostly nest between August and November, the desert species have been recorded breeding in all months of the year.
The Western whip bird was at one time considered rare or even endangered, but once its haunting, ventriloquistic call was learned it was discovered in several places in southern Australia. Several species oflogrunners have been affected by the clearing of forest or the overgrazing of shrubland in Australia, though none is currently threatened.
To many people, the Australasian warblers are just dull little brown birds. However, they are of great scientific interest because they display a variety of complex breeding biologies.
The Gerygone warblers are the most widespread members of the group occurring in Australia, New Guinea, Indonesia, Malaysia, Burma, New Zealand, and many Pacific Islands. They are delicate attractive birds with tinkling songs that flitter through the foliage after tiny insects. Scrub-wrens inhabit the understory of forests in Australia and New Guinea and thornbills are principally Australian, where they forage in a range of sites from the ground to the treetops.
Most Australasian warblers are small, even tiny, with short tails and wings and fine hills. Although many are dull brown or olive, many thorn bills have contrastingrumps and the Gerygone warblers often have bright yellow underparts. The Rock warbler, which nests in caves in sandstone around Sydney, NSW, is dark gray above and reddish brown beneath. In appearance, the sexes and ages are similar, often identical.
Insects are the primary food, but the whitefaces, which live in dry habitats, eat a lot of seeds. Where several species ofthombill occur in the same place each usually forages at a different level in the vegetation.
Evidence is slowly emerging that hornbill, despite their tiny size (7–rog,0.2 5-0.28oz) are long-lived, with-year-old birds being quite frequent in populations studied. Perhaps due to this they often do not breed in their first year. Breeding takes place from late winter to summer, and although some species breed as pairs cooperative breeding is more typical of the group.
The Buff-tailed thornbill lives in clans of about ten birds for most of the year. At the beginning of the breeding season, these break up into pairs, trios, and quartets which attempt to breed. Those that fail in their breeding attempt help a neighboring pair or group. until the clan comes together again in the fall. A change in foraging coincides with the breakup of the clan. Larger groups feed more on the ground and pair on the harbor among the foliage.
Australasian warblers frequently join and may lead feeding flocks of mixed species in the non-breeding season, a habit that does not help the bird-watcher confronted with a host of species of little brown birds.
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