Class AVES Order PASSERIFORMES Suborder OSCINES Family ORIOLIDAE (ORIOLES AND FIGBIRDS) free text Handbook of the Birds fo the World
Medium-sized passerines with relatively large, long and pointed wings, short to medium-length tail; many species very colourful in yellow to golden and black, some more green.
Woodland, forest and parklands.
2 genera, 30 species, 92 taxa.
3 species threatened; none extinct since 1600.
The orioles and figbirds form a small and well-defined family of highly arboreal, medium-sized bird species inhabiting woodlands, forests and parklands of the warmer parts of the Old World, mainly in Africa and tropical southern Asia eastwards through Wallacea and New Guinea to Australia. Different authors have recognized between 25 and 30 species in the family, and with differing species limits within this range. In the present treatment, Oriolidae comprises 30 species in two genera: Sphecotheres, containing the figbirds, and Oriolus, with the orioles. Figbirds are distinguished on the basis of the possession of bare red skin around the eye and their colonial nesting habits. Among the orioles proper, some early taxonomists separated a sombre-coloured group of Australasian species, which they placed in the genus Mimeta, from the generally brightly coloured Afro-Asian species, which constituted the genus Oriolus, but R. B. Sharpe, in his 1877 review of the family, combined them all in Oriolus. This arrangement was continued in a 1923 review by R. Meinertzhagen, who pointed out that the only criterion for retaining Mimeta would be that the species involved lacked the brilliant colours of adult Oriolus; in all other respects, however, the two groups are closely similar. Meinertzhagen also reasoned that the family might be Australo-Papuasian in origin, rather than, as had formerly been assumed, Oriental. His argument was based on the fact that adults of the former regionâ€™s Mimeta group retained a striped plumage like that of juveniles of the brightly coloured Afro-Asian species, and the fact that the genus Sphecotheres is confined to eastern Indonesia, New Guinea and Australia. Meinertzhagen envisaged two distinct branches arising from Australasia. The first involved the two maroon species, namely the Maroon Oriole (Oriolus traillii) and the Black-and-crimson Oriole (Oriolus cruentus), in South-east Asia; this branch, linked to Mimeta, he thought, by the Black Oriole (Oriolus hosii), did not spread to the Palearctic or Africa. The second branch produced the bright black-and-yellow orioles, linked to Mimeta by the Isabela Oriole (Oriolus isabellae) and the Philippine Oriole (Oriolus steerii), over the rest of Eurasia and Africa.
Traditionally, the Oriolidae were considered to be most closely related to the drongos (Dicruridae), the crows (Corvidae), the leafbirds (Chloropseidae) and the fairy-bluebirds (Irenidae). On the basis of evidence obtained in analyses of DNAâ€“DNA hybridization, however, C. G. Sibley and J. E. Ahlquist found the oriolesâ€™ immediate closest relatives to be the cuckoo-shrikes (Campephagidae). These authors placed the orioles and cuckoo-shrikes together in a tribe, the Oriolini, in the subfamily Corvinae, within their much-expanded family Corvidae. Although the link between the orioles and the cuckoo-shrikes is corroborated by the results of protein studies and some similarities in osteological traits, other morphological differences suggest that the retaining of Oriolidae and Campephagidae as separate families is the preferable course of action. Although Sibley and Ahlquistâ€™s family Corvidae also includes the drongos, DNAâ€“DNA hybridization does not support a close relationship between the drongos and the orioles. More recent sequencing of nuclear genes reveals the leafbirds and the fairy-bluebirds to be even more remote from the orioles. Thus, although taxonomic syntheses based on the sequencing of both mitochondrial and nuclear genes have provided a finer and perhaps more reliable resolution of some parts of the oscine tree, as shown by, for example, the 2003 study by P. G. P. Ericson and U. S. Johansson, they have not so far directly affected the lower-level inter-familial relationships of the orioles as suggested by Sibley and Ahlquist in 1990.
As a matter of interest, it is worth mentioning the position of the Madagascan genus Tylas. It has been suggested that this genus, which contains a single species, Tylas eduardi, might be closely related to the Oriolidae. Current opinion, however, is that it is a vanga, and it is generally therefore placed in the Vangidae, a family confined to Madagascar and the nearby Comoro Islands. Nevertheless, the true systematic position of the Tylas Vanga may perhaps merit further study.
Molecular-genetic techniques have not yet been used as a means of investigating species limits within the family Oriolidae, and these still rely on conventional characters such as osteology, plumage and voice. Although the genus Oriolus appears remarkably homogeneous, with no need for subdivision, as was recognized by Sharpe, Meinertzhagen and, most recently, J. C. Greenway in J. L. Petersâ€™s Check-list of Birds of the World, attempts have nevertheless been made at one time or another to introduce some substructuring, by proposing alternative genera or subgenera in which to group similar species. Five such suggestions have been made. The first of these involves the original Australasian genus Mimeta, erected by N. A. Vigors and T. Horsfield in 1827, and comprising dull brown to olive-green species with striped underparts. This name has been used to group the Green Oriole (Oriolus flavocinctus) with the Brown (Oriolus szalayi), Dusky-brown (Oriolus phaeochromus), Grey-collared (Oriolus forsteni), Black-eared (Oriolus bouroensis), Olive-brown (Oriolus melanotis) and Olive-backed Orioles (Oriolus sagittatus). These last six were considered by Sibley and Monroe and by R. Schodde and I. J. Mason to form a superspecies.
The alternative genus Xanthonotus, originally described by C. L. Bonaparte, in 1854, has been used to group the Dark-throated Oriole (Oriolus xanthonotus), the Philippine Oriole and the Isabela Oriole, the first two of which were considered by Sibley and Monroe to be sister-species. The subspecies albilorus of the Philippine Oriole has sometimes been elevated to the rank of a full species, but in other treatments the Philippine Oriole, including albiloris, has been considered a subspecies of the Dark-throated Oriole.
African Oriole, near Serrakunda, Gambia. Picture by Jan Dolphijn
C. M. N. White, in 1986, considered the Eurasian Golden Oriole (Oriolus oriolus), African Golden Oriole (Oriolus auratus), Slender-billed Oriole (Oriolus tenuirostris) and Black-naped Oriole (Oriolus chinensis), the so-called â€œyellow-headed groupâ€, to constitute a superspecies, to which the Indian Golden Oriole (Oriolus kundoo), now separated from the Eurasian species, can be added. Four years later, however, Sibley and B. L. Monroe treated these taxa as comprising two sets of sister-species: O. oriolus, with kundoo as a subspecies, and O. auratus forming one set, the other consisting of O. chinensis and O. tenuirostris.
In the Afrotropics, the â€œAfrican black-headed groupâ€, comprising the Green-headed (Oriolus chlorocephalus), Sao Tome (Oriolus crassirostris), Western Black-headed (Oriolus brachyrhynchus), Ethiopian Black-headed (Oriolus monacha), Mountain (Oriolus percivali), Eastern Black-headed (Oriolus larvatus) and Black-winged Orioles (Oriolus nigripennis), could be considered to belong to the alternative genus Baruffius, created by Bonaparte in 1854. Sibley and Monroe regarded the Western Black-headed and Ethiopian Black-headed Orioles as sister-species, and the Eastern Black-headed and Mountain Orioles similarly to be sister to each other.
Finally, the alternative genus Analcipus, created by W. Swainson in 1832, has been used to accommodate the Black Oriole, Black-and-crimson Oriole, Maroon Oriole and Silver Oriole (Oriolus mellianus). These, together with the Black-hooded Oriole (Oriolus xanthornus), have been referred to as the â€œAsian black-headed groupâ€. Within this group, the Maroon and Silver Orioles were considered sister-species by Sibley and Monroe.
As it is not clear to what extent plumage characteristics among orioles, on which much of the above grouping rests, carry a strong phylogenetic signal, we cannot be confident that such substructuring accurately reflects evolutionary relationships within the oriole family tree. Given also that some species, such as the Black-naped Oriole, are undoubtedly polyphyletic as presently constituted, a molecular-genetic reappraisal of the Oriolidae is much needed.
Schodde and Mason, in 1999, proposed that the genus Sphecotheres should be placed before Oriolus in the systematic sequence, because they regard Sphecotheres as the ancestral taxon. This is the practice currently adopted.
Orioles and figbirds are medium-sized, robust passerines 20â€“30 cm in length. The sexes are of similar size, although the female is usually slightly smaller than the male. Orioles have a slightly decurved and finely hooked bill which is about equal in length to the head. It varies, however, from being long and slender, as with the Slender-billed Oriole, to being robust, deep and broad, as is the bill of the Sao Tome Oriole and some races of the Black-naped Oriole, to being rather short and like that of a bulbul (Pycnonotidae), as demonstrated by the Western Black-headed Oriole. Figbirds differ from orioles proper in having a very short bill. In the case of the Eurasian Golden Oriole, at least, the juvenileâ€™s iris is light brown and usually becomes progressively redder with age. Likewise, the bill of the juvenile is dark reddish-brown, changing to pale red in adults. Orioles have relatively large, long and pointed wings with ten primaries, the outermost, P10, being about half the length of the adjacent one (P9), with primary P8 the longest. The tail is square, short to medium length, and has twelve rectrices. The tarsi are relatively short but strong, and the feet are also short but rather weak; they are apparently not used in feeding.
Many species of oriole are colourful, at least in the adult male plumage, which is often patterned in brilliant golden-yellow and black colours. The family name may derive from the Old French oriol, which may, in turn, have come from the Latin aureolus, meaning â€œgoldenâ€, or it may be just an onomatopoeic rendition of a common oriole call (see Voice), or it could be due to both possibilities. It was applied originally to the Eurasian Golden Oriole, but the males of many other species in the family are also mostly golden-yellow with black wings, the African Golden Oriole being a good example, although some Oriental species have the yellow replaced by crimson or silvery white. Those species having yellow in the plumage possess a dull red or pink bill, whereas those with red in the plumage have a horn-coloured or bluish bill. Figbirds are much duller in plumage, being predominantly dull yellow, green, brown and grey or white, with a black or brownish bill. Within the Oriolidae, there are occasional documented records of melanistic individuals or individuals with other colour aberrations.
Although the adult plumages of male and female orioles are mostly well known, the sequence of immature plumages as young birds moult from juvenile to adult is not. Among species in which the sexes differ strongly in adult coloration, sexual differences usually become apparent after the second moult. In general, the immature plumage of females can be expected to resemble a duller version of the adult female, but in the case of males of such species, or with orioles in which adults of both sexes are brightly coloured, an immature may pass through a more complex sequence, especially if sexual maturity is delayed. For many of the oriole species this has been poorly recorded, and further research is required. As adults, orioles apparently moult once per year.
Eurasian Yellow Oriole, near Byalistok, Poland. Picture by Jan Dolphijn
Eurasian Yellow Oriole, near Byalistok, Poland. Picture by Jan Dolphijn
Orioles and figbirds vary in the degree of sexual dichromatism exhibited. Some species are distinctly dichromatic, with the female quite different from and much less brightly coloured than the male. Examples include the Eurasian Golden Oriole and the African Golden Oriole, the females of which retain an olive-green, streaked plumage like that of an immature, although, on rare occasions, females strongly resemble the males. With about half of the species, however, the female resembles the male or is only slightly duller. This is so in the â€œAfrican black-headed groupâ€, which comprises the Eastern Black-headed, Western Black-headed and Ethiopian Black-headed Orioles, the Mountain Oriole and the Black-winged Oriole; also included with these species are the Green-headed Oriole, which has the black pigment of the head replaced by green, and the island endemic the Sao Tome Oriole, which resembles a â€œwashed-outâ€ version of the mainland species. The â€œ Asian black-headed groupâ€ includes four species, the Black, Black-and-crimson, Maroon and Silver Orioles, which exhibit no yellow but, instead, have this colour substituted by red, brown or silver. These species are sexually dichromatic, although the degree to which this is expressed varies. In the case of the Black-and-crimson Oriole, uniquely, two subspecies are strongly dichromatic and two are apparently monochromatic. Several Australasian species, however, lack bright coloration in both sexes and are generally greenish above and streaked below, resembling the females and immatures of the African and Asian species that are strongly dichromatic. In this respect they are similar to the figbirds, both sexes of which are also greenish above and streaked below, the most conspicuous sexual dichromatism being in the colour of the bare skin around the eye, which is red in the male and bluish-grey in the female.
The drab brown or olive-green coloration of several Australasian species of oriole may be unimpressive in itself, but it is remarkable in that it closely mimics the plumages of species of friarbird (Philemon) having ranges that coincide with those of the orioles themselves. The mimicry in coloration includes the possession by the orioles of black-feathered areas that match areas of black bare facial skin on the friarbirds, and the similarities are so close that even specimens held in the hand may be confused. This plumage mimicry is reinforced by similarities in posture, movements and flight, as well as by vocal mimicry in two species, so that orioles and friarbirds may be even harder to distinguish in the field, even though the latter are members of a different family, the honeyeaters (Meliphagidae). Thus, in New Guinea, the Brown Oriole is similar visually and also vocally to the Helmeted Friarbird (Philemon buceroides), although it is streaky below and lacks the friarbirdâ€™s bill knob. The Dusky-brown Oriole on Halmahera is a close visual mimic of the Dusky Friarbird (Philemon fuscicapillus) and difficult to distinguish in the field, and on Seram the Grey-collared Oriole is virtually identical to the Seram Friarbird (Philemon subcorniculatus). The two subspecies of the Black-eared Oriole, one on Buru and the other in the Tanimbar Islands, are each closely similar visually to the respective island races of the Black-faced Friarbird (Philemon moluccensis) and are said also to be vocal mimics. On Wetar, the female of the local race finschi of the Olive-brown Oriole is quite similar to the local Helmeted Friarbird but the male is less so, while on Timor, where the nominate race of this oriole occurs, the female is again quite similar to the Helmeted Friarbird but the male is not. In Australia, however, where both the Olive-backed Oriole and the Green Oriole overlap in range with the Helmeted Friarbird, there is no mimicry.
It seems clear that the orioles mimic the friarbirds, rather than vice versa. The brown plumage and black facial skin are shared by all except one species of friarbird and by many other meliphagids, but the combination of brown plumage and black facial feather patches is unique among orioles. Furthermore, sister-taxa with identical plumage in the same friarbird superspecies occur on many islands where the mimicking orioles do not, yet the mimetic orioles are virtually confined to islands with friarbirds. A further intriguing fact is that, the greater the size disparity between friarbird and oriole, the more perfect is the mimicry. Orioles in this superspecies are rather uniform in body mass, whereas the friarbirds vary from oriole-sized to roughly twice this. The Seram Friarbird is the largest and is approximately 78% heavier than the Grey-collared Oriole, which is an almost perfect mimic of it. The friarbirds on Halmahera, Buru and Tanimbar are about 50% larger than the Dusky-brown Oriole and the two races of the Black-eared Oriole, respectively, and the mimicry of these last is close but not perfect. In New Guinea and on Wetar, the friarbirds are about 39% heavier than the Brown and Olive-brown Orioles, respectively, and the mimicry is even less good. On Timor, where the friarbird is only some 13% larger than the Olive-brown Oriole, the mimicry is fair in the female but absent in the male, and it is lacking altogether in both sexes of the Olive-backed and Green Orioles in Australia, where the local friarbirds also average only 12% larger. A further twist to the story is that the Brown Oriole in New Guinea is itself closely mimicked, both visually and vocally, by another meliphagid less than half its size, the Streak-headed Honeyeater (Pycnopygius stictocephalus).
These size relationships between models and mimics suggest that smaller birds are mimicking larger ones, rather than its being a case of Batesian mimicry, in which palatable orioles may avoid predation by mimicking a distasteful friarbird model. There is no evidence that friarbirds are distasteful, nor would Batesian mimicry explain why another honeyeater would mimic an oriole. J. M. Diamond has plausibly suggested that the frequent incidence of attacks among orioles, friarbirds and other honeyeaters might provide a strong selective force for the evolution of size-dependent mimicry. These birds have similar habitat preferences and regularly feed together in the same flowering and fruiting trees, exhibiting a broad overlap in their diets of insects, fruit and nectar. There is a great amount of fighting within these feeding assemblages, with a dominance hierarchy based on size and aggressiveness, the larger birds, friarbirds especially, being more combative and more successful. Nevertheless, Diamond, during his studies in New Guinea, never observed an attack by a Helmeted Friarbird on a Brown Oriole, nor an attack by a Brown Oriole on a Streak-headed Honeyeater, despite the fact that these regularly fed within a few metres of each other and frequently attacked other species. In north-east Australia, however, he saw the same friarbird species attack and drive off the smaller non-mimetic Green Oriole, and in south-east Australia the non-mimetic Olive-backed Oriole stands its ground when attacked by the similar-sized Noisy Friarbird (Philemon corniculatus), and either species may win or lose a fight. Diamondâ€™s suggestion is that mimics, by convergence in appearance, escape attack by larger models that might otherwise drive them away; and, the greater the size disparity between oriole and friarbird, the more perfect the mimicry had to be for the oriole to assert itself against an increasingly large aggressor. Although the Australian populations of the Olive-backed Oriole do not mimic friarbirds, they may mimic the Australasian Figbird (Sphecotheres vieilloti). The plumage of both sexes of the former is very similar to that of the female figbird, and the oriole often feeds with figbird flocks and may nest close to figbird breeding colonies. The Olive-backed Orioleâ€™s behaviour is secretive in the presence of figbirds, which ignore it, whereas the presence of other species usually elicits an aggressive response.
Orioles are primarily canopy feeders (see General Habits). Almost all members of the family have been recorded in primary forest habitats of various kinds: dry, closed-canopy African woodlands, evergreen and semi-evergreen broadleaf forests, including monsoon forest, damp highland and moss forests, eucalypt (Eucalyptus) woodland, and deciduous and coniferous forests, as well as mixed forests such as pineâ€“oak (Pinusâ€“ Quercus) forest.
Nevertheless, with the exception of the globally threatened and Near-threatened species (see Status and Conservation), which appear to be particularly dependent on large undisturbed tracts of closed-canopy forest, most orioles seem to prefer semi-open woodland habitats over completely closed forests, even when taking into consideration the possibility of observer bias due to the fact that birds are more easily observed in open habitats. These open woodland habitats can also be of various kinds, although they are structurally rather similar to one another. Thus, 20 oriole species have been recorded in forest edges, including treefall gaps and small overgrown clearings, 19 in relatively mature second growth, 16 in semi-open woodlands, 15 in cultivated areas with large trees, 13 in tall riverine vegetation such as gallery forest, twelve in plantations, twelve in gardens, nine in parks, five in windbreaks and avenue trees, five in groves and five in orchards. Other, similarly open habitats include bushes, scrub and thickets, in which eleven oriolids have been recorded, mangroves, with ten species, swamp-forests, with five, and bamboo forests, in which three have been found. In a particularly comprehensive study, S. Baumann monitored the movements of breeding Eurasian Golden Orioles in northern Germany. Using telemetry, she found that movements varied strongly from one breeding pair to another depending on habitat geometry, time of the breeding season and, concurrently, food supplies. Forested habitats were clearly preferred, but tree plantations, parks, gardens and isolated groups of trees, such as avenue trees, were also popular, while treeless habitats were almost completely avoided.
Although orioles are usually bound to tree-dominated habitats, they do nevertheless sometimes exploit other habitats opportunistically. In particular, the Eurasian Golden and Indian Golden Orioles are found in open deserts and high mountain regions during migration. While the Eurasian Golden Oriole does no more than rest on stopover at Saharan oases while on passage through Africa, the Indian Golden Oriole breeds in such places, as, for example, in oasis plantations in the Kyzyl-Kum Desert, south-east of the Aral Sea. The Eurasian Golden Oriole also forages in treeless heath and among sand dunes on almost treeless islands, using the few trees present for breeding only. Thus, the breeding requirements of these species may sometimes be as simple as a tree with a suitably shaded forked branch for nesting and sufficient invertebrate food available in the foliage or on the ground.
Orioles are highly arboreal, generally foraging secretively alone or in pairs. Despite the conspicuous plumage of most of the species, orioles are usually hard to see against a leafy forest background dappled by the sunâ€™s rays, and they seem deliberately to hide from the observer, although their characteristic calls (see Voice) reveal their presence. Even in flight, orioles may be inconspicuous. The typical flight pattern is swift, silent and undulating, as the bird closes its wings at regular intervals, in the manner of a woodpecker (Picidae). They have a powerful but somewhat irregular wingbeat, reaching average speeds of 40â€“47 km/h, and a male can achieve up to 70 km/h when chasing another male. In their favoured, tree-dominated habitats they will typically fly from treetop to treetop, never staying in the open for long. Before landing on a perch, they typically sweep upwards with half-opened wings. Orioles can hover for short periods, with an upright body posture and fast-beating wings, looking not unlike a miniature kestrel (Falco), in order to observe or catch a food item or when building a nest. Figbirds, on the other hand, are gregarious and travel in noisy flocks of up to 100 or more individuals. A feeding flock may remain in a fruiting tree until it is virtually stripped clean, the birds even hanging upside-down on the ends of twigs to reach the last fruits. Many oriole species, especially in the tropics, also occasionally gather in small groups in fruiting or flowering trees, and regularly join marauding mixed-species flocks in the search for food; these mixed flocks can comprise a dozen or more different bird species. Likewise, up to ten individuals may congregate in a small area wherever caterpillar densities are high. Although orioles generally sleep solitarily, evening roosts can at times attract dozens or even hundreds of individuals to the same place. Usually, however, individuals or pairs keep away from each other in widely spaced feeding territories, younger individuals floating in and out of these territories. For the Eurasian Golden Oriole, for example, feeding ranges have an average extent of about 40 hectares, but vary between 7 ha and 110 ha, while defended territories around the nest are much smaller, at about 1Â·3 ha, ranging from 0Â·7 ha to 2Â·3 ha.
Territorial advertisement and defence against conspecifics involve calls and songs (see Voice), most singing taking place in the morning and evening from exposed and regularly used perches high in the tree canopy. The calling frequency decreases in bad weather and also after the young have hatched. In order to escalate the threat against an intruder, the Eurasian Golden Oriole turns from side to side and ruffles its neck feathers while giving a more varied song than usual, and with increased volume, speed and intensity. It may then resort to an aggressive stance, with the wings held open, the tail fanned and the head stretched forward, aided by short, loud calls, wing-beating and beak-snapping, or it may even hover in front of the intruder. Finally, chases and physical attack ensue, and these can, in rare instances, lead to injury or death through collision in the air or impact with the ground resulting from the birds interlocking their feet.
With their often brightly coloured plumage but self-concealing habits, it is difficult to know how vulnerable adult orioles may be to predation. Orioles are probably regularly attacked by birds of prey, but reports of such events are only anecdotal. When in a situation in which they feel threatened, orioles usually fixate on the danger for a short period, in motionless posture, before they retreat to a higher perch in the canopy. When encountering unexpected noises or other potential threats while foraging on the ground, however, the Eurasian Golden Oriole immediately seeks cover. In attempts to avoid an attacking Eurasian Sparrowhawk (Accipiter nisus), one individual reportedly escaped into a woodpecker hole, and another hid under the edge of a roof. A further individual of this species hid in dark rock crevices to escape the attentions of an Eleonoraâ€™s Falcon (Falco eleonorae). Migrating Eurasian Golden Orioles are frequently captured by Eleonoraâ€™s Falcons in the Mediterranean region and by Sooty Falcons (Falco concolor) in Ethiopia. Other raptors recorded as preying on this oriole are the Booted Eagle (Hieraaetus pennatus), Red (Milvus milvus) and Black Kites (Milvus migrans), the Common Kestrel (Falco tinnunculus), the Red-footed (Falco vespertinus), Lanner (Falco biarmicus) and Peregrine Falcons (Falco peregrinus), the Northern Goshawk (Accipiter gentilis) and the Eurasian Buzzard (Buteo buteo), and the Eurasian Eagle-owl (Bubo bubo), Northern Long-eared Owl (Asio otus), Ural Owl (Strix uralensis) and Tawny Owl (Strix aluco) have also been recorded as taking Eurasian Golden Orioles as prey. Peregrine Falcons and Japanese Sparrowhawks (Accipiter gularis) attack and sometimes kill Black-naped Orioles, and Black SparrowÂhawks (Accipiter melanoleucus) and Peregrines have both taken Eastern Black-headed Orioles.
South American Yellow Oriole, near Paramaribo, Surinam. Picture by Jan Dolphijn
An intriguing anti-predator response is exhibited by adult Eurasian Golden Orioles, which, when threatened, adopt a stiff posture with beak turned upwards, similar to that of a bittern (Botaurus) when disturbed or alarmed. This behaviour is demonstrated also by fledglings when warned by their parents, and it is already evident even among nestlings; the latter, if a parent gives a warning call, press themselves flat into the bottom of the nest but keep the bill pointing upwards. Dodging all dangers, ringed Eurasian Golden Orioles reached a maximum age of eight years, with an average of 1Â·5 years for ringed nestlings and 3â€“4 years for individuals that had reached adulthood.
Orioles must drink, and they may do so in various ways. The Eurasian Golden Oriole, for example, may pump or suck water, as well as nectar, upwards into its downward-pointed beak, or it may use a sequence of alternately pumping and raising its beak, a â€œsuck-and-tiltâ€ process. Usually, this species drinks from tree hollows, takes dew or raindrops from branches or leaves, or flies closely above the surface of a waterbody and quickly dips its bill. In rare instances, it will also drink from rain puddles.
The Eurasian Golden Oriole bathes by diving down rather steeply from a waterside tree or bush, splashing briefly on to the surface of the water and immediately returning to the original perch or another one, a method recorded also for the Indian Golden Oriole. Alternatively, the former species will bathe in the manner of swallows (Hirundinidae), by gliding just above the water and briefly dipping its breast and belly. It will also bathe in shallow water along the waterâ€™s edge or in wet foliage, and, during rainshowers, several individuals have been observed to hang upside-down from a branch, with the wings held open. Bathing is usually followed by an extensive and vigorous grooming bout in order to rearrange and clean the feathers, a task for which orioles prefer high and covered perches. A group of Australasian Figbirds, for example, started rain-bathing high up in some fig trees (Ficus) by lowering the head and fanning the tail; the birds then slowly slid under the perching branch into an upside-down position, where they cupped the wings for 1â€“3 seconds, after which they returned to an upright position to shake, ruffle and groom the entire plumage. This performance was repeated several times. An Olive-backed Oriole rain-bathed in a similar upside-down position, but with its head thrown back, its wings fully opened and its tail fully fanned. Orioles may also sun-bathe, but the function of this behaviour is less clear, as it may be used for comfort, for thermoregulation or for the control of ectoparasites. Anting has not been recorded for any of the family.
As already mentioned (see Morphological Aspects), a plausible alternative explanation for the origin of the name â€œorioleâ€ is that it is onomatopoeic. Although this derivation is associated with the Eurasian Golden Oriole, which does, indeed, utter a clear â€œo-ri-oleâ€ call, the songs and calls of many other species in the genus Oriolus have the same sweet, liquid, fluting characteristics, making them immediately recognizable as emanating from an oriole. Similarly widespread among the Oriolus species, having been recorded from at least 17 species, is a harsh nasal call, variously described as growling, sneezing or screeching, or a cat-like â€œmiaouwâ€. Figbirds, on the other hand, utter a series of simple tuneless whistles and short sharp yelps.
The complexity of oriole calls varies greatly among the species. Several species, instead of producing clear musical calls, will at times emit a prolonged jumble of syncopated sweet notes, as demonstrated by the Black-hooded Oriole. The Philippine Oriole delivers a series of often rapidly repeated simple syllables for an extended period, and the Dark-throated Oriole accompanies such a vocalization with tail-flicking; in the case of the Black-naped Oriole, several individuals join together in producing this rapid series. Three of the species in the â€œAfrican black-headed groupâ€, namely the Black-winged Oriole and the Eastern Black-headed and Western Black-headed Orioles, have very varied and extensive repertoires, and another in that group, the Sao Tome Oriole, also exhibits much variation. Three species in this group, the Mountain, Eastern Black-headed and Black-winged Orioles, may extend their calls into a duetting sequence between male and female. Similarly, the Eurasian Golden Oriole will perform a quiet antiphonal duet, and in New Guinea the Brown Oriole also duets, but the latterâ€™s performance is poorly synchronized.
Western Black-headed, Eastern Black-headed, Brown and Olive-backed Orioles are excellent vocal mimics of several other species. In the case of the Brown Oriole, this includes its visual mimic, the Helmeted Friarbird, the call of which the oriole also uses in the duetting sequence. Likewise, the Black-eared Oriole is said to be a vocal mimic of the Black-faced Friarbird, which it closely resembles in appearance (see Morphological Aspects). The vocalizations of orioles have provided some corroborative support in taxonomic diagnoses, most recently as one of the characters separating the Eurasian Golden and Indian Golden Orioles at the species level. In other cases, some clear vocal differences among taxa have not yet persuaded taxonomists that they provide sufficient evidence for the â€œsplittingâ€ of species. As an example, the call of the â€œWhite-lored Orioleâ€ is different from that of the Philippine Oriole, within which it is currently placed as the subspecies albiloris, and the extensive racial differences within the Black-naped Oriole complex remain largely unstudied.
Food and Feeding
Orioles are omnivorous and almost exclusively arboreal, foraging mainly high in trees. They feed chiefly on berries, fruits and invertebrates, with some other foods taken opportunistically. The latter include, for example, nectar, pollen, flowers, flowering shoots, leaf buds, seeds of, among others, barley, oats and grasses, and vertebrates such as lizards and small mammals, as well as bird eggs and nestlings. While the three Sphecotheres figbirds feed mostly on fruits, the Oriolus species take much more animal food, although the proportion of fruits to invertebrates in the diet varies widely, depending on sex, age, habitat and season. As an example, the Eurasian Golden Oriole apparently consumes more fruit during migration and winter than it does during the breeding period, and it feeds its young with progressively more fruit, if this is available, as they grow.
Foraging orioles keep mainly to the canopy and middle storey, where they detect food items mostly by sight but sometimes by sound, and then glean or snatch these from branches and foliage. While searching for food, orioles move through the vegetation in short flights and hops or by climbing, but they may also use other body postures, including hanging upside-down, in order to reach food. Sometimes, they will catch insects, such as winged termites (Isoptera), in mid-air, and they are able also to hover in a kestrel-like manner to glean items from the undersides of leaves or to locate prey from close above. Orioles sometimes forage in lower levels of vegetation if a good food source is available, as along forest edges or in clearings, treefall gaps or fruiting shrubs. Rarely, however, are they seen to forage on the ground, a substrate which they usually exploit only when pursuing large invertebrates or in mostly treeless habitats. In pursuit of terrestrial prey they often hover before pouncing to the ground, where they hop or briefly fly but rarely walk.
Orioles consume a wide variety of invertebrates. Recorded dietary items include earthworms (Oligochaeta), leeches (Hirudinea) and snails (Gastropoda), and arthropods such as spiders (Araneae) and a multitude of insect taxa. Among the last, damselflies and dragonflies (Odonata), crickets, katydids, grasshoppers and locusts (Orthoptera), preying mantises (Mantodea), termites, mealy bugs (Pseudococcidae), shield bugs (AcanthosoÂmidae), jewel bugs (Scutelleridae), stink bugs (Pentatomidae), cicadas (Cicadidae), weevils and other beetles (Coleoptera), snakeflies (Raphidioptera), mantid flies (Mantispidae), caddis flies (Trichoptera), gadflies (Tabanidae), hoverflies (Syrphidae), craneflies (Tipulidae), moths and butterflies (Lepidoptera), and such Hymenoptera as wood wasps (Siricidae), diprionid sawflies (Symphyta), ichneumon wasps (Ichneumonoidea), ants (Formicidae), hornets and wasps (Vespidae), and bumblebees and bees (Apoidea) have all been recorded as prey. Besides consuming adult invertebrates, orioles eat eggs, pupae and larvae, an orioleâ€™s apparently favourite meal being caterpillars, both hairless and hairy. It is worth remembering that hairy caterpillars are a potential food item that is avoided by most other bird species.
In addition to animal food items, orioles take an equally wide variety of fruits and berries, including those of alien species. The figbirds are, as the vernacular name implies, very fond of figs, but no fewer than 16 oriole species have been observed also to take figs, and it is likely that most other species take these fruits but have not so far been recorded as doing so. Orioles do not shy away from commercial orchards, either, and they are therefore sometimes considered agricultural pests. As a consequence they are persecuted at times (see Status and Conservation), especially during migration periods, when large numbers may assemble in the same orchard. Less easily digestible food items, such as hairy caterpillars or hard-shelled insects, and fruits are typically prepared for up to five minutes before being consumed. This preparation involves the pressing, mandibulating, shaking or ripping of the item, or the vigorous brushing and pounding of it against a hard surface, usually the perch, but the bird does not use the feet to hold the prey while it is being prepared in this way. Such manipulation makes caterpillars, for example, more digestible by removing their hairs and pulping the body, and it is often employed by the adults before feeding such items to the young. Likewise, the parents sometimes squeeze fruits so that the juice enters the mouth of the young chicks. Hard indigestible food items, such as chitinous body parts of insects, are later regurgitated.
Breeding seasons are determined by seasonal climatic patterns, some tropical species breeding throughout the year. While knowledge of the breeding behaviour of many oriole species is only rudimentary or non-existent, what we do know reveals an astonishing uniformity within the family, so much so that the details for many of the species are more or less identical to those pertaining to other species. Again, more is known about the breeding behaviour of the Eurasian Golden Oriole than about that of any other oriolid, but, apart from the figbirds, the breeding behaviour of the other members of the family appears to be very similar. So far as is known, all orioles are socially monogamous, but, whereas those in the genus Oriolus evidently defend exclusive territories, the Specotheres figbirds breed in loose colonies.
Courtship among orioles consists mainly of calls and aerial chases, the male flying, diving, hovering, wing-beating and tail-fanning in view of the female. Aerial chases are sometimes followed by copulation. The male whistles and hops around the female, and she entices her partner with screeching calls and by fanning her tail to one side to allow the male to mount. This he does up to four times, after which he may resume hopping or chasing. Copulation usually takes place on branches or on the nest. It is not known whether females elicit secretive extra-pair copulations. More rarely, several males may engage in lek-like courtship displays directed at a single female, features of which include aerial chases involving two males or one male and a female, and simultaneous or interchanging calling.
A very elaborate courtship display by a male Eastern Black-headed Oriole was observed in Kenya. Having flown down to the branch of a small tree, the male fanned his tail, partly opened his wings, depressed his head, and, in this position, slowly revolved on the branch. He then bent down, suddenly brought his fanned tail over his back, and lowered his wings and spread them fully. Throughout the performance, the oriole called continuously with a mixture of imitations of starling (Sturnidae), sunbird (Nectariniidae) and robin-chat (Cossypha) calls interspersed with the liquid notes which the male of this species ordinarily utters. After a short silence, he displayed again, but this time with the head raised and the neck outstretched, the fanned tail held high, and the wings partially opened and held low on the branch as he bobbed up and down.
After pair formation, the partners start combine to look for potential nest-sites, which may be anywhere within the pairâ€™s feeding territory. Several Asian and Australasian species will deliberately select a nest-site near the nest of more aggressive species, such as drongos, butcherbirds (Cracticidae) or friarbirds, which may afford some protection against nest predators. For example, both Slender-billed and Black-hooded Orioles will nest near Black Drongos (Dicrurus macrocercus), the Brown Oriole may nest near Hooded Butcherbirds (Cracticus crassicus) or Helmeted Friarbirds, and the Olive-backed Oriole may seek out nesting colonies of Australasian Figbirds, while the Australasian Figbird, in turn, may nest in association with Helmeted Friarbirds or Spangled Drongos (Dicrurus bracteatus). Likewise, the Eurasian Golden Oriole occasionally builds its nest near those of, for example, Fieldfares (Turdus pilaris), Great Grey Shrikes (Lanius excubitor) or Lesser Grey Shrikes (Lanius minor).
The typical oriole nest is a shallow to deep, open cup densely woven from various plant materials, decorated with moss and lichens, and suspended hammock-like in a thin, horizontal fork on a lateral branch high inside a well-foliaged tree canopy. If a suitable support is not available, the oriole will often create one by weaving together several thinner branches. The nest is very tough and capable of withstanding severe storms. It is built mostly or entirely by the female, the male sometimes helping by collecting some nest material; the building work is completed within 1â€“2 weeks, exceptionally longer. Figbird nests, by comparison, are not woven and are simpler and flimsier structures, loosely put together from twigs and with no inner lining. Nest-building requires pliable material for fixing the main structure, soft material for lining, and other material suitable for camouflage. Materials utilized for nest-building are probably chosen opportunistically, as is illustrated by the use of animal items such as hair, feathers and even snakeskin, and man-made materials such as paper, string, plastics and textiles, once even stolen from a scarecrow. Around the beginning of the twentieth century, one lucky finder retrieved a 1000 franc banknote from a nest. During the First World War, a nest of the Eurasian Golden Oriole was found to have been made entirely of surgical dressings pilfered from a nearby dressing-station; after the Second World War, nests made almost entirely out of aluminium strips dropped by bombers to deflect the enemyâ€™s radar were found. Most nesting material, however, is plant-based and from a variety of sources, sometimes stolen from the nests of conspecifics or other species.
While building the nest, the female may alight in a neighbouring tree, before secretively hopping to the nesting site itself a little way away. She often uses saliva both to soften vegetable fibres and to glue the first few strips, 20â€“40 cm in length, to the branches, and frequently uses cobwebs for binding. After tightly wrapping the preliminary strips around the holding branches to produce a basic hammock-like structure, the female then intricately weaves further vegetable fibres into the basic structure, using her beak to pull fibres from the outside to the inside of the nest and from the inside to the outside. Once the nestâ€™s structure has reached a certain degree of sturdiness, its shape is constantly improved by the female, which turns one way and the other and presses her body against the inside.
Oriole clutches vary from one egg to six, but the average is about two to three eggs, usually laid at intervals of 1â€“2 days. The eggs measure approximately 2 Ã— 3 cm and weigh 5â€“10 g. They are sometimes white or pinkish-white but mostly some sort of creamy colour, with reddish, brownish, purplish, greyish and blackish spots and streaks, these markings usually concentrated at the obtuse end. The eggs of figbirds, however, are duller, having a greyish-green to olive-brown ground colour.
Although, with some members of the family, it appears that both sexes build the nest, incubate the eggs, and brood and feed the nestlings, this is the exception. More usually, it is exclusively or almost exclusively the female that incubates, for a period of 2â€“3 weeks, and that broods the nestlings, again for 2â€“3 weeks. While incubating, the female of the Eurasian Golden Oriole leaves the nest to feed herself only for brief periods of about ten minutes, and rarely up to 38 minutes, but she leaves for longer foraging trips after the eggs have hatched. Meanwhile, the male may feed her and he may also incubate or brood for short periods.
The nestlings of orioles and figbirds are altricial and nidicolous. Both sexes feed them, in the early stages mostly with small invertebrates, especially caterpillars, but later also with larger invertebrates and more and more berries and fruits, if these are available. The proportion of regurgitated food, as opposed to fresh, unregurgitated food, decreases as the young grow. In the case of the Eurasian Golden Oriole, the best-studied species, both male and female feed the chicks, at a rate of around 9â€“15 times per hour, but sometimes up to 24 times per hour, and with up to 211 feeds in a day. Nestlings begin to beg clamorously, with the open bill upward-turned, as soon as they feel the vibrations and hear the sounds of an arriving parent; after opening their eyes at about 6â€“8 days of age, they also detect the parentsâ€™ presence visually. The parents at first swallow the chicksâ€™ faecal sacs, but they carry them away from the nest once the young are about 8â€“1 0 days old, at which time the chicksâ€™ digestion has become so efficient that their faecal sacs no longer contain any appreciable residual nutrients. Brood-feeding decreases or ceases altogether during the hot midday hours or during periods of bad weather, when nestlings will cuddle together for warmth and, in strong winds, use their claws to cling tightly to the bottom of the nest. During heavy rainfall, the female protects the nestlings by sitting on top of them; at times of intense heat, she may shade them while they pant to lose heat and, in such conditions, the chicks often spread out to such an extent that their heads may protrude over the edge of the nest.
Adverse weather decreases nesting success by depleting food resources, particularly invertebrates, or by directly killing nestlings or destroying nests. After such events, depending on circumstances, pairs may quickly make a new breeding attempt, or they may forgo breeding for the year in question. Exceptionally bad weather, such as hailstorms, can even kill adults.
South American Yellow Oriole, near Paramaribo, Surinam. Picture by Jan Dolphijn
Orioles use several strategies to defend the nest against predators and conspecifics. One is, as mentioned in the preceding paragraphs, to build the nest in close proximity to the nests of other, combative species, which may themselves chase off a potential nest predator. If danger approaches, however, the female crouches low in the nest, or slinks away quietly to hide nearby, returning only once the danger has passed. Potential nest predators such as cats, martens (Martes), mice (Muridae), squirrels (Sciuridae), shrikes, starlings, and such corvids as ravens, crows, magpies and jays, as well as owls (Strigidae) and birds of prey, are actively chased away, the oriole sometimes defecating on them, and neighbouring pairs occasionally joining in. Orioles rarely resort to direct physical attack, but in a few instances they have been recorded as actually killing an intruding predator by using the bill. Known nest parasites of orioles, such as the Common Koel (Eudynamys scolopaceus) and other cuckoos (Cuculidae), are also chased away. Once the young start begging for food, a warning call by one of the parents silences them immediately and causes them to crouch motionless in the nest.
Telemetric studies of the Eurasian Golden Oriole in northern Germany showed that, during the breeding season, the adults foraged for 45% of the time within 200 m of the nest and for 80% of the time within 700 m of the nest, but they would travel 1â€“3 km for especially abundant food sources, such as plants infested with caterpillars. Their foraging ranges increased significantly after the hatching of the eggs. Sometimes, up to three immature or adult orioles, presumably previous offspring of the nesting pair, helped in the feeding of the young, especially in habitats with poor food availability. A similar phenomenon has been recorded for the Australasian Figbird, the nestlings of which are occasionally brooded and fed by extra males and females.
Nestlings of the Eurasian Golden Oriole begin to preen and to exercise their wings when they are about 10â€“12 days old, which is the time when most down feathers start to be replaced with adult feathers. A few days later, some leave the nest and perch in the immediate surroundings, including the ground. They start to fly when 16â€“20 days old, after which the young stay with the parents in family groups for a few weeks, or perhaps even months, feeding by the parents eventually ceasing altogether. Orioles probably breed for the first time at the age of 2â€“3 years, as demonstrated for the Eurasian Golden Oriole.
Studies of Eurasian Golden Orioles have revealed that this species can exhibit site-fidelity over several years. In a few cases, ringing has confirmed that both male and female returned to the same territory year after year. Usually the pair chooses a new nesting site, but occasionally it will occupy the same nesting tree or, indeed, the same branch, and it may even reuse materials from the previous yearâ€™s nest or, rarely, the orioles will use the old nest, merely repairing it with some new material. Both the Eastern Black-headed Oriole and the Eurasian Golden Oriole have on rare occasions been recorded as using the same nest a year later.
Among the Oriolidae, only two species are long-distance migrants the entire populations of which move seasonally. The Eurasian Golden Oriole migrates between breeding grounds in the Palearctic Region and non-breeding areas in the Afrotropics, and the Silver Oriole moves between southern China, where it breeds, and Thailand and Cambodia, where it spends the non-breeding season. In eight other species, only parts of the population are migratory while others are sedentary; these are the Olive-backed, Indian Golden, African Golden, Black-naped, Slender-billed, Eastern Black-headed, Black-hooded and Maroon Orioles. The remaining 20 species in the family are largely sedentary, but may move short distances in response to food fluctuations, or the young may roam about, or â€œfloatâ€, while seeking to establish new territories. Whether individuals fly only a few kilometres or thousands of kilometres, the overriding reason for movements is the search for adequate food supplies, largely in the form of fruits and invertebrates (see Food and Feeding). It is usually, therefore, that part of the population living in areas where the winters are harshest that migrates, while sedentary populations are found in more stable climates.
Most is known about the migration of the Eurasian Golden Oriole, but the movement-related habits of this species are probably similar to those of other orioles which migrate. Migration is usually preceded by heavy bouts of feeding to promote the accumulation of fat reserves, a phenomenon observed also for the African Golden Oriole. Spring migration is faster, more direct and more diurnal than is autumn migration. This is because the males are competing to establish breeding territories as early as possible, and because the females, although usually arriving up to ten days later than the males, need to reach the breeding grounds in time to begin nesting in the optimal period. No such pressing needs push the birds during autumn migration, when the Eurasian Golden Oriole migrates at a more leisurely pace and reportedly mostly at night, probably in order to avoid predators (see General Habits). Adverse weather can be another threat, as it is known to delay by up to several weeks the spring migration of both the Eurasian Golden Oriole and the Black-naped Oriole.
Eurasian Golden Orioles usually migrate alone or in small flocks of up to 30 individuals, although hundreds may gather around fruit resources, especially in gardens and orchards. In exceptional circumstances, even larger concentrations are recorded; for example, thousands were seen together south-west of Alexandria, in north Egypt, on 27th April 1982. Flight altitude can vary. Recorded heights during diurnal passage southwards vary between 5 m and 100 m while over land, many orioles then crossing the Mediterranean Sea at altitudes of 200â€“300 m but ascending to 1500â€“2000 m on reaching the Sahara. Within the Afrotropics, with no need for breeding, the only consideration for Eurasian Golden Orioles becomes that of staying alive. This requires mainly that they follow the wet season as it moves southwards across the continent, since rainfall triggers the growth of green vegetation and a subsequent bonanza of caterpillars and other large invertebrates.
Relationship with Man
Several oriolids, among them the Eurasian Golden Oriole, the Eastern Black-headed Oriole and the Australasian Figbird, occasionally cause damage to fruit crops in gardens and orchards, and have consequently been persecuted. It is very likely that other oriole species have met the same fate.
Orioles have been exploited by humans for food, sport hunting, the cagebird trade, taxidermy and medicine and for their eggs (see Status and Conservation). In the Altai Mountains of Central Asia, orioles were used by shamans in their religious rituals. Farther west, in the Chuvashskaya Republic of European Russia, the cooked feathers of the Eurasian Golden Oriole were believed to cure malaria and yellow fever, and in Hungary the nests of this species were burnt to produce a cure for mastitis in cows. African Golden Orioles were occasionally sold in markets in Nigeria, probably for traditional medicinal purposes, and the flesh of the Black-naped Oriole has been eaten by pregnant women in South-east Asia supposedly to make their babies more beautiful.
The Eurasian Golden Oriole is considered a harbinger of summer in Europe, and has been called the â€œWhitsun-birdâ€ because of its late arrival in central Europe, the religious festival of Whitsun, or Pentecost, coming seven weeks after Easter. This species has been named also the â€œ beer-birdâ€, because Whitsuntide used to be marked by a festival with a lot of merriment and ale-drinking. It has also been called â€œrain-birdâ€ or â€œrain-catâ€, as it is sometimes the only bird to sing in the humid weather conditions that precede a thunderstorm. K. D. Feige, in his German-language monograph of the Eurasian Golden Oriole, lists more than one hundred colloquial names for this species. For example, this speciesâ€™ dietary preferences are reflected in such colloquial names as â€œcherry-thiefâ€, â€œfig-eaterâ€ and â€œgrape-thrushâ€, just as the name â€œmango-birdâ€ for both the Indian Golden Oriole and the Black-hooded Oriole indicates one of the favourite feeding trees of these members of the family. The Indian Golden Oriole has been endowed also with the native name of Peeluk, meaning â€œThe Yellow Oneâ€, on account of its brilliant plumage, and the Eurasian Golden Oriole, similarly, has colloquial names such as â€œyellow-birdâ€, â€œgold-birdâ€, â€œgold-thrushâ€ and â€œolive-thrushâ€ in Arabic, English, German, Icelandic, Luxembourgish, Norwegian and Swedish.
The mournful whistled song of the Eurasian Golden Oriole evokes sad feelings in some people, apparently especially so among Russians. This is evidenced by the poem by the Russian writer Anna Akhmatova entitled â€œI hear the always-sad voice of the orioleâ€, which salutes the passing of the summer, as well as by the documentary movie â€œSomewhere laments an orioleâ€¦â€, by the Russian film-maker Edmond Keosayan, which tells the story of a Russian girl who, during the Second World War, was brought from Russia to Belgium, where she became an active Resistance fighter. Another book referring specifically to orioles is R. Trevelyanâ€™s The Golden Oriole: Childhood, Family and Friends in India, in which the author describes his journey across India as he revisits the places of his childhood and evokes the spirit of the British experience in colonial India. Finally, one of Germanyâ€™s best-loved comedians, Vicco von BÃ¼low, whose last name is itself an onomatopoeic spelling of the orioleâ€™s song, adopted the French name of the oriole, Loriot, as his stage-name. The Eurasian Golden Oriole is quite a popular bird in Germany, at least, with three excellent German monographs published in the last two decades. That by Feige has been mentioned in the preceding paragraphs; the other two are by E. Bezzel and R. Wassmann. Bezzelâ€™s monograph celebrates the oriole being awarded the title of â€œBird of the Yearâ€ in 1990, an honour bestowed annually on a particular bird species by the German BirdLife partner in order to raise conservation awareness among the general public.
Status and Conservation
Of the 30 species of Oriolidae currently recognized, three are globally threatened and a further three are listed as Near-threatened. This total of six species amounts to 20% of the family, the same as the global average for all avian families. Top of the list is the Critically Endangered Isabela Oriole of the north Philippines, rediscovered in 1993 after a 32-year absence of records, followed by the Sao Tome Oriole and, in south China, the Silver Oriole, the current status of each of which is considered to be Vulnerable. The Dark-throated Oriole, the Black Oriole and the Wetar Figbird (Sphecotheres hypoleucus) are thought not yet to be at immediate risk and are placed in the conservation category of Near-threatened.
The Isabela Oriole is apparently dependent on the lowland rainforests, and especially thick bamboo forest, on the Philippine island of Luzon, where it has had to contend with a 75% reduction of its habitat over the last century. Although this species has been recorded also in second growth and forest edges, primary forest habitat is probably of crucial importance for its continued survival. Likewise, the Sao Tome Oriole and the Silver Oriole appear to be dependent mainly on primary forest, utilizing mature secondary forest to a far lesser extent. Of the Near-threatened species, the Dark-throated Oriole and the Wetar Figbird use both primary and secondary forests, while the Black Oriole seems to be restricted to primary forest.
All six of these species have relatively small global ranges, predisposing them to extinction, but the ultimate causes of their precarious status are anthropogenic, principally habitat loss, degradation and fragmentation brought about by logging, agricultural expansion and, to a much lesser degree, other forms of Âhuman encroachment such as road-building, mining and uncontrolÂled fires. Pesticide use is also implicated in the decline of the Sao Tome Oriole. In reality, it is not really known how dependent many of the 30 oriole species are on primary, undisturbed forest for long-term survival or whether they could also survive in patches of secondary forest. The protection of large tracts of forest must, therefore, be considered essential in view of the current limited knowledge of these speciesâ€™ ecology. The conservation of the Silver Oriole is further complicated by the fact that this oriole migrates between breeding grounds in China and non-breeding areas in Thailand and Cambodia, thereby necessitating conservation strategies for both regions.
South American Yellow Oriole juvenile, near Paramaribo, Surinam. Picture by Jan Dolphijn
Yellow Oriole juvenile, near Paramaribo, Surinam. Picture by Jan Dolphijn
Encouragingly, all globally threatened and Near-threatened members of the family except the Wetar Figbird occur in one or more protected reserves, with further areas in the process of becoming protected. Nevertheless, it remains highly questionable whether these limited forest patches will suffice to ensure the long-term survival of each species, in particular because some of these reserves are poorly managed and inadequately protected. All except one of the six oriolids that are threatened or potentially threatened have been observed in degraded forest habitats, which may enable them to survive in a patchwork of primary and secondary forest remnants. It is not known, however, whether they can successfully breed in degraded or secondary habitats, which may therefore act as population â€œsinksâ€, these species still being completely dependent on primary habitats for survival. The Black Oriole, the only threatened or potentially threatened species that has so far been recorded only from primary forest habitats, may make use of secondary habitats, too, but not yet have been observed in them.