Distribution
The starling family is restricted to the Old World, except where man has introduced species elsewhere. Within the Old World, starlings have radiated into many geographic regions and occupied many habitats within them. Geographically, they range over the whole of Africa and west to the Azores, Europe north to c. 68°N, Asia north to c. 65°N, Japan and the Kurile Islands, the Indian sub-continent, Indonesia, New Guinea, islands of Micronesia east to c. 165°E, Melanesia south to c. 32°S, Polynesia east to c. 160°W, and in Australasia extend into northern Queensland. Within this range occur species of wide distribution, such as Amethyst Starling that occurs over most of sub-Saharan Africa and Common Starling that occurs over much of Europe and Asia, and species restricted to small islands.
This range embraces a wide diversity of habitats and starlings have penetrated most of them; these include forests, both evergreen and deciduous, humid and dry, and montane and lowland, although the absence of starlings in the highland forests of New Guinea is notable. Starlings also inhabit more open environments, including forest edge and open woodland, savanna, riparian valleys, arid semi-desert and of course cultivated areas.
Representatives are found in montane forest on Pacific islands, but these species are island endemics and most species in Oceania, New Guinea and Indonesia tend to be birds of the lowlands, where they inhabit forest, forest edge and clearings. Many of these species appear to be resident. In India and mainland South-East Asia, starlings occur throughout, with species in montane forest and extending into the Himalayan foothills; here again, however, most species occur in the lower areas, but including the Deccan plateau. The lowland starlings of India, Indochina and the large islands of Java and Sumatra have developed specialisations that enable them to exploit terrestrial food sources and this has been accompanied by a more insectivorous or even omnivorous habit. The evolution of these traits paved the way for starlings to enter more open, and especially more arid, areas and this enabled some forms to colonise the vast steppes of southeastern Europe and Central Asia, and ultimately the temperate grasslands so extensively expanded by man’s activities. These areas possess rich food resources in terms of both invertebrates and fruit, but these resources are highly seasonal in their availability, and in response to this seasonality the starlings that colonised these more northerly areas evolved long-distance migrations.
These migrations are generally north-south, with birds that breed in eastern Europe and Asia returning to the tropics or subtropics in winter. In western Europe, Common Starlings sometimes winter to the southwest, or even west, of their breeding area and some populations, towards the west and southwest of their breeding area, are resident. After breeding, the young of several of the species that breed at higher latitudes undergo a dispersal, sometimes into habitats such as marshes and moorlands, which are not normally exploited by them. Some of these dispersals can be highly directional, e.g. Swiss-breeding Common Starlings move northwest to the North Sea and Atlantic seaboard prior to undertaking their autumn migration to the south. In India, Chestnut-tailed Starlings undertake movements, possibly migrations, so that at certain times of year the distinctive races Sturnus malabarica malabarica and S. m blythii may be found in the same area, even in mixed flocks (Ali and Ripley 1972); the nature of these movements is not understood. Brahminy Starling also undertakes movements in the monsoon, but again these are not fully understood except for the movement of northern populations which are known to be summer visitors to this breeding area. Spot-winged Starling is both an altitudinal and an east-west migrant, breeding in the western Himalayan foothills and migrating east through Nepal and Sikkim to winter commonly in Assam. This species is often associated with Chestnut-tailed Starlings both in the breeding and non-breeding areas.
Within Africa also, there are forest starlings and savanna starlings, and birds whose range is centred on high, rocky areas, although they will forage in various surrounding habitats. In contrast to Eurasia, only two species, African Pied Starling and Wattled Starling, occur regularly in treeless, grassy areas. The birds of high rocky ground may be found above 4000 m, and undergo extensive altitudinal movements, even on a daily basis in species such as Slender-billed Red-winged Starling. This group also includes several species which may be found in arid, desert areas. The forest starlings fall into two clear groups: birds of lowland forest, and those of montane forest. They are all primarily birds of the forest canopy, and only one species, the Black-bellied Glossy Starling of the coastal belt, is regularly found at low levels within the forest. Most of the African starlings occur within the savanna vegetation zone, and within this broad category they may be found in all areas from moist to arid regions.
The forest starlings are primarily West and Central African in their distribution, with three montane forest species in East Africa and only a single species ranging from eastern to southern Africa, in coastal forest. Purple-headed Glossy and Coppery-tailed Starlings show a distribution suggesting separation of the parental population and subsequent speciation when the forest was subdivided into western and eastern blocks at the Dahomey Gap in West Africa (Hall and Moreau 1970). The other lowland forest species today show a continuous distribution in the central area, with no morphological differences to confirm any past separation. The two East African montane species, Kenrick’s and Stuhlmann’s Starlings are separated by the Rift Valley, yet a third species, Waller’s Red-winged Starling, has populations on both sides of the Rift Valley and also occurs on the Mount Cameroon massif in West Africa. This implies a longer history for Waller’s Red-winged Starling, with a former distribution over areas which today represent unsuitable habitat.
The starlings of rocky habitats include Tristram’s Red-winged Starling, apparently isolated on the Arabian peninsula by the formation of the Red Sea rift, and a species endemic to the island of Socotra. In this group, three species have a distribution centred on Ethiopia and another is restricted to eastern Africa. The most widespread member of the group is Red-winged Starling, with a range from temperate South Africa to Ethiopia, although the West African populations, formerly treated as a race of Red-winged Starling, are here regarded as a separate species, Neumann’s Red-winged Starling, derived from one of the other Ethiopian species (Craig 1988a).
One savanna species, Amethyst Starling, is the most widespread African starling, with breeding populations in western, eastern, and southern Africa. Two other species, Greater and Lesser Blue-eared Glossy Starlings, also range over these three regions, but their southern African distribution is much more restricted than that of Amethyst Starling. The remaining savanna-woodland birds show four general patterns of occurrence: West African, in some cases extending as far east as the Nile valley; East African; Central African in the Brachystegia vegetation belt; and southern African, extending northwards to Central or East Africa. This group contains several species endemic to eastern Africa, with some such as Ashy Starling having an extremely restricted total range. The Rift Valley and the Ethiopian highlands seem to define the northern and western limits of an area in which these endemics have evolved; by contrast there is only a single endemic of southern African origin, African Pied Starling (Craig 1985). Pale-winged Starling, now virtually restricted to southern Africa, may have originated from an Angolan ancestor (Craig and Hulley 1992).
The movements of starlings within Africa are still poorly understood, although detailed seasonal data for several countries are now available in the form of bird atlases. The most recent attempt at a synthesis of such movements by Curry-Lindahl (1981) did little to advance our knowledge, and the best synopsis of migration within Africa remains the account by Chapin (1932). He mentioned the two species in which migration is best documented, Splendid Glossy Starling and Amethyst Starling. Traylor (1971) provides a good picture of the movements of Amethyst Starling, and these show some resemblance to the regional migrations of Red-billed Quelea Quelea quelea (Ward 1971, Elliott 1990), with the rainfall regime in different parts of Africa determining the movements between breeding and non-breeding areas. The Amethyst Starling’s savanna woodland habitats are highly seasonal in terms of rainfall, and thus food availability, but its distribution does not extend into any temeperate regions. There is a small inter-continental component to its migration, with birds visiting the southern Arabian peninsula to breed.
In marked contrast to most other migratory species, Splendid Glossy Starling is found in tropical forest at all seasons. In this habitat many frugivores show irregular movements related to food abundance, but it seems clear that this species is a true migrant, at least in the southern populations, which are breeding visitors to Zambia and southern Zaïre. Much further study is required to provide a full picture of its movements.
The two species of semi-arid areas in East Africa, Magpie Starling and Hildebrandt’s Starling, apparently show regular migratory movements linked to rainfall (Lewis and Pomeroy 1989). Other African starlings may be nomadic in the non-breeding season, but their movements are too localised and erratic to justify the term migration. This is supported by a detailed analysis of the seasonal occurrence of Wattled Starling, based on both museum specimens and on data from bird atlas schemes (Craig 1996).
Habitat use and social behaviour
Starlings show a wide variety of social behaviours, some of which vary with habitat and geographical location. Social behaviour during breeding is described in the chapter on breeding and its associated activities, while here we discuss social behaviour during activities that are not directly related to breeding, but are related to habitat use.
Few starlings live a solitary existence, Brown-winged and Shelley’s Starlings being the only well-documented cases in which solitary breeding is usual, but out of the breeding season the latter species associates in flocks (Britton 1980). Others for which solitary behaviour has been described are mainly species living on islands, such as Mountain Starling and Pohnpei Mountain Starling, and which live in the forest canopy. These are comparatively rare and unknown species and our impression of their lack of social activity may reflect their scarcity or the difficulty of seeing them. The majority of Asian and Pacific starlings, including most species of Aplonis, and many African species display tendencies to be more gregarious, at least in some situations.
Most members of the genus Aplonis are largely frugivorous but also include insects in the diet. They are generally found in pairs or small groups but some gather in larger numbers at particularly good food sources, e.g. fruiting trees. Two species, Shining Starling and Asian Glossy Starling, depart from the typical Aplonis social behaviour in that they regularly occur in large flocks, and also roost communally in large assemblages at night. These traits are associated with a more opportunistic diet in these two species, and also with a geographical range encompassing larger land masses than in other species.
The members of the largely frugivorous genera Mino, Basilornis, Streptocitta and Ampeliceps also generally associate in pairs, although Yellow-faced Myna regularly feeds in larger flocks and sometimes groups of over 200 birds roost together at night. The monotypic and somewhat aberrant Sulawesi endemics, Flame-browed Starling and Grosbeak Myna, also frequently form large flocks; in the latter species this may be associated with their extreme form of colonial breeding, and the constant vocalisation within feeding flocks doubtless serves to maintain flock cohesion. The significance of the greater propensity of these two largely frugivorous species to form flocks will, however, be elucidated only when more is known of their general biology. Hill mynas tend to show a somewhat greater plasticity in behaviour in that, although largely frugivorous and feeding and roosting in pairs or small family groups, they demonstrate opportunism by, at times, congregating in large flocks to feed in fruiting or flowering trees.
The emphasis on opportunism is taken further by the Acridotheres and Gracupica mynas, and this is accompanied by a more omnivorous diet, involving a much higher proportion of insects and other animal matter and a greater tendency to feed on the ground. Terrestrial feeding has involved a switch from hopping, the form of locomotion used by arboreal frugivores, to walking and running. In these genera we also see the development of prying, the technique that permits the procurement of food items by probing in the surface vegetation or even into the soil. The ability to employ this feeding action has involved modifications of skull shape, eye position and movements, and jaw musculature. These developments have also been accompanied by changes in social behaviour, and although these mynas associate in pairs throughout the year, pairs coalesce into large flocks whenever suitable concentrations of food appear. These species usually roost communally at night (except when breeding), sometimes in huge assemblages and often in company with other starling species. Acridotheres and Gracupica mynas are also highly vocal, using a wide repertoire of calls throughout the day and indulging in intensive bouts of singing during preparation for roosting and during roost departure in the morning; the function of this song in roosts and pre-roost assemblies is not known. The adaptations that facilitated the opportunism of these mynas in exploiting transient abundances of food also permitted the birds to take advantages of similar locally abundant but transient food sources made available by man. These food sources take many forms - cultivation of land, ripening crops grown in monocultures, abundances of flowering and fruiting trees, facilities for storing and disposing of human waste - and the act of creating human settlements and their associated facilities has often involved the removal of forest and the creation of open ground dominated by herbaceous vegetation, thus making available the kind of habitat that these mynas are pre-adapted to exploit. In consequence, these mynas often live in close association with man.
The six species of Sturnia retain a more arboreal habit but nevertheless have a broad diet, including insects, fruit and seeds, and are also opportunistic in their exploitation of temporary superabundances of food. While White-faced and White-headed Starlings are island endemics and probably sedentary, other members of the genus are more mobile. Chestnut-tailed Starling undertakes local movements allowing it to capitalise on seasonally available food, while Red-cheeked, Purple-backed and White-shouldered Starlings exploit seasonally abundant food supplies, especially insects, in temperate regions by migrating north to breed. This trait is taken to its extreme by Rose-coloured Starlings which, in the breeding season, rely upon insect swarms, especially grasshoppers and locusts, in the more arid regions of Central Asia and eastern Europe. This is paralleled in Africa by Wattled Starling, whose movements are more nomadic in their exploitation of insect infestations, again primarily grasshoppers and locusts. As soon as breeding is over, these species revert to a broader diet, including fruits and seeds whose availability is temporary. In association with their exploitation of ephemeral resources, these species form large flocks and roost communally.
In the genus Sturnus, Common and White-cheeked Starlings have combined the opportunism and terrestrial habit seen in Acridotheres species with northward migration to breed, enabling them to exploit the spring flush of surface and sub-surface insects in temperate grasslands. Their opportunism also permits them to capitalise on other temporary superabundances of food made available by man’s agricultural activities and his by-products. After the breeding season, juvenile and adult Common Starlings tend to segregate but both age groups become more omnivorous. In migratory populations both adults and young leave the breeding areas, form flocks and begin to roost communally at night. Communal roosts are largest in winter and at this time adults and 1st-winter birds roost together. The behaviour associated with communal roosting is spectacular and complex, however, involving assembly in ever larger flocks by birds approaching the roost site, coordinated aerial manoeuvres immediately prior to entry, much vocalisation while settling in the roost and before departure, segregation of age and sex classes within the roost and during morning departure, and extreme synchronisation of exoduses of groups of birds during departure (Summers and Feare 1995). The significance of this behaviour is not fully understood.
African starlings are mostly omnivorous, feeding opportunistically on whatever food is most readily available, and even some forest canopy species, which have been categorised as specialist frugivores by Snow (1981), take many insects as shown by their stomach contents. Nevertheless, there is certainly a division between arboreal species, with proportionately short legs and a large component of fruit in the diet, and the longer-legged terrestrial foragers which take a high proportion of animal food. As with Asian species, African starlings take seeds on occasion but none can be termed granivorous.
The most specialised African starlings, with respect to diet, are the oxpeckers, which feed almost exclusively on ticks and other ectoparasites plucked or combed from the body surface of large mammals. Using similar movements, they also feed on blood and body fluids from their hosts. Their legs and claws are modified for clinging in woodpecker-like posture, while the bill shape is distinctive and associated with the stereotyped feeding movements. Three other starlings of rocky areas, with relatively short legs and strong grasping claws have regular grooming associations with ungulates in Africa and Arabia: Red-winged, Pale-winged and Tristram’s Red-winged Starlings (Gargett 1975, Tilson 1977, Yosef and Yosef 1991). However, some predominantly terrestrial starlings, such as African Pied Starling (Craig 1987) and the Acridotheres mynas will also remove ticks from both domestic and wild mammals.
African starlings are also sociable, to varying degrees, outside the breeding season. Commonly, family groups form at the end of the breeding period and in cooperative groups, e.g. in African Pied Starling, members of a breeding unit remain together throughout the year (AC, pers. obs.). These groups may link up while foraging to form flocks of up to 100 birds in many species, and in a few cases very large flocks may form at roosts; these often assemble from a wide area and are clearly not associated as feeding groups during the day. More than 1,000 birds may be found in roosts of Wattled Starlings (Liversidge 1961), African Pied Starlings (Every 1975), Lesser Blue-eared Glossy Starlings (A J Tree, pers. comm.), Purple Glossy Starlings (Thonnerieux et al. 1989), Burchell’s Glossy Starlings (R K Brooke, pers. comm.) and Red-winged Starlings (AC, pers. obs.). The largest assemblages may be those of Splendid Glossy Starlings, for which Brosset and Erard (1986) reported that nocturnal roosts in Gabon during the dry season may contain tens of thousands of birds.
The sexually dimorphic Amethyst Starling seems to be the only species in which the sexes may form separate flocks (Traylor 1971). Long-tailed Glossy Starlings in savanna may join members of other bird families in mixed species feeding flocks (Moynihan 1978), and so do Splendid Glossy Starlings in forest (Prigogine 1978). These associations are assumed to provide extra security against predators, but there have been few studies of the correlates of mixed species flocking in Africa. Ground-feeding starlings may be found alongside other sympatric starlings, or birds such as weavers, and in this situation there may also be benefits in awareness of predators. Wattled Starlings sometimes roost in association with Greater and Lesser Blue-eared Glossy Starlings and, in South Africa, with African Pied Starlings (Liversidge 1961), but in this case the key factor is probably the choice of similar roosting habitat.
Vocalisations
Starlings are not normally thought of as great songsters, compared to families such as the thrushes whose voices are more musical to our ears. Nevertheless, the song of Common Starling is very complex and has been the subject of much research in recent years (for a review see Eens, 1977). Motifs from a captive bird were evidently used as a theme in a score by the composer Mozart (West and King 1990).
Vocalisation plays an important role in intra-specific communication, and during the breeding season is used by males to advertise status and possession of a nest site to females, but it may also attract potential rival males to the area (Mountjoy and Lemon 1991). Song is also used outside the breeding season. Many African starlings gather in trees during the middle of the day or at other times, and vocalise in ‘choirs’ for long periods. It is not known whether both sexes are involved, nor whether such choruses have any special function in the social organisation of the species. In winter, flocks of Common Starlings may be found throughout the day in the tops of bare trees near good food sources, and such flocks keep up a constant cacophony of song. Both sexes participate and although the function of this song is not known, Summers and Feare (1995) have suggested that it may be used by overflying birds to assess the extent of competition likely to be encountered if these birds attempted to feed at the site.
Many species of starling are also vocal in their communal night roosts, especially as the birds settle at the roost site and as they prepare to depart in the morning. Where birds roost in city centres, the noise made by the birds is sometimes regarded as a nuisance of sufficient importance to warrant some form of control, e.g. as in urban roosts of Common Starlings, and Common and White-vented Mynas. In Common Starlings, both sexes are known to participate in this song but its function is uncertain; however, it does seem to play a role in perch acquisition and defence (CJF, pers. obs.).
In Red-winged Starling, the musical whistling calls serve for communication between the members of a pair, and are likely to be individually distinct. Duetting has been noted between members of a pair in Brahminy Starlings (Sontag 1985b) and in Rüppell’s Long-tailed Glossy Starling in Kenya (Dittami 1987). Most starlings have distinctive flight calls in their vocabulary, but harsh alarm calls are very similar between species and are mutually recognisable. Mammals, such as the hosts of the oxpeckers, and the monkeys found alongside ground-feeding starlings in East Africa, can also learn to respond to starling alarm calls (Hauser 1988).
Hill mynas are renowned for their abilities to imitate human speech in captivity, but in the wild they do not imitate the calls of other species but do imitate the calls of neighbouring hill mynas (Bertram 1970). Sonographic analysis of their mimicry of the human voice shows that it is a very accurate representation of the trainer’s voice (Klatt and Stefanski 1974). Vocal mimicry has been reported for several African starlings in the field (Vernon 1973) and is well-known in Common Starling (Hindmarsh 1984, Hausberger et al. 1991). Common Starlings are also capable of mimicking human speech but this ability seems to depend upon a very close bond between the bird and its foster parent (West et al. 1983). There is now clear evidence that Common Starlings are unusual among birds in continuing to learn new song elements, from sounds in their natural environment, throughout life (Bohner et al. 1990, Eens et al. 1992). Recently, neurological studies have identified the brain areas involved in such learning in this species (Uno et al. 1991).