|At Tswalu Kalahari Reserve, South Africa|
A. Smith, 1837
The sociable weaver (Philetairus socius) is a species of bird in the weaver family, endemic to Southern Africa. It is the only species in its genus Philetairus. It is found in South Africa, Namibia, and Botswana, but its range is centered within the Northern Cape Province of South Africa. The species builds large, compound, community nests, a rarity among birds. These nests are perhaps the most spectacular structure built by any bird.
Taxonomy and systematics
The sociable weaver was first described by ornithologist John Latham in 1790. Alternative names include the common social weaver, common social-weaver, and social weaver. Formerly, four subspecies were recognised, but the species is now considered monotypic. The sociable weaver is the only extant species in the genus Philetairus.
Based on a 2017 DNA-analysis, P. socius belongs to the group of sparrow weavers (subfamily Plocepasserinae) and is most related to the genus
Measuring around 14 cm (5+1⁄2 in) in length, the sociable weaver has a black chin, black, barred flanks, and a scalloped back. It typically weighs 26–32 g (15⁄16–1+1⁄8 oz), and sexes are indistinguishable.
Distribution and habitat
The species ranges across northwestern South Africa and southwest Botswana, and extending northwards across Namibia. It is strongly associated with the arid savannas characteristic of the southern Kalahari region. The presence of stiff grasses such as Stipagrostis ciliata (syn. Aristida ciliata) – an important nesting material – is an important determinant of its distribution. The taller grasses and the fire-prone nature of the Northern and Central Kalahari regions may be a factor for the absence of the bird in those regions. The area is semiarid with low and unpredictable rainfall occurring mostly in the summer. The population has not been quantified, but the birds are described as "common to abundant".
Behaviour and ecology
In the southern range of the weaver's habitat, breeding may occur any time of the year and is closely linked to rainfall. In the northern range, a discrete breeding season between December and August has been noted. They may skip breeding during years when rainfall is low and a substantial number (sometimes over half) of birds in the colony may never breed in a given season. Under typical conditions, weavers raise up to four broods per breeding cycle. Sociable weavers are known to assist in the care of younger siblings and unrelated hatchlings, and nearly all pairs are assisted by helpers. A mating pair has been recorded as producing nine broods in a single season in response to repeated predation of its young. Unlike northern temperate passerine birds, which commence breeding within the first year of life, sociable weavers exhibit delayed-onset breeding, at sometimes up to two years of age.
Sociable weavers construct permanent nests on trees and other tall objects. These nests are amongst the largest built by any bird, and are large enough to house over 100 pairs of birds, containing several generations at a time. The nests are highly structured and provide birds with a more advantageous temperature relative to the outside. The central chambers retain heat and are used for nighttime roosting. The outer rooms are used for daytime shade and maintain temperatures of 7–8 °C (45–46 °F) inside while outside temperatures may range from 16–33 °C (61–91 °F).
The nests consist of separate chambers, each of which is occupied by a pair (sometimes with offspring) and used to roost and breed. Nests are built around large and sturdy structures such as acacia trees or sometimes even telephone poles. The trees generally used for nest-building are
Sociable weaver nests form a habitat that is occupied by animals of many different taxa, including several other bird species, which use the nest in different ways, such as for breeding (as with the
Reptile species also use the nests. Snakes, especially Cape cobras and boomslangs, are the most common nest predators, often consuming all the eggs in all the chambers of a large nest. Nest predation is often as high; in one study, 70% of the clutches laid were preyed upon. In addition, Trachylepis spilogaster (Kalahari Tree Skink) associate with the nests. Trees with nests appear to host more skinks than trees without nests. Additionally, these skinks have learned to eavesdrop on sociable weaver alarm calls to determine when a pygmy falcon, one of its main predators, is approaching.
Nests built in electricity poles sometimes cause short circuits in the rainy season and can catch fire in the dry season.
The sociable weaver is insectivorous, with insects comprising 80% of their diet. As an adaptation to living in the dry Kalahari Desert, where standing water is scarce, the sociable weaver obtains all of its water from its diet. it also feeds on seeds and other plant products. Foraging is predominantly on the ground, but also on bark and leaves of trees.
Populations of the sociable weavers increased during the 2010s, perhaps due to increased availability of nesting structures such as electricity pylons and other man-made structures. Most of its present distribution is unlikely to see any major man-made alteration and its future in these areas is secure. A gap seen in its distribution in the Northern Cape Province, north of the Ghaap Plateau is probably due to habitat alteration by clearance of Acacia. In other areas, encroachment due to overgrazing may also cause local extinction.
Adult arriving with nesting material
Chamber entrances seen from below
A nest on an electricity pole
- . Retrieved 11 November 2021.
- Covas, R. (2002). Life-history Evolution and Cooperative Breeding in the Sociable Weaver (PDF) (PhD). Percy Fitzpatrick Institute - University of Cape Town. Retrieved 18 January 2011.
- Mendelsohn, J.M.; Anderson, M.D. (1997). "Sociable Weaver Philetairus socius" (PDF). In J.A. Harrison; D.G. Allan; L.G. Underhill; M. Herremans; A.J. Tree; V. Parker; C.J. Brown (eds.). The Atlas of Southern African Birds. Johannesburg: BirdLife South Africa. pp. 534–535. Archived from the original (PDF) on 2006-10-15.
- Collias, Nicholas E; Collias, Elsie C. (January 1977). "Weaverbird nest aggregation and evolution of the compound nest" (PDF). The Auk. 94: 50–64. Retrieved 18 January 2011.
- "Common names for Sociable Weaver (Philetairus socius)". Encyclopedia of Life. Retrieved 28 March 2014.
- "ITIS Standard Report Page: Philetairus". Integrated Taxonomic Information System. Retrieved 28 March 2014.
- "Birds: Sociable Weavers". San Diego Zoo: Animals and plants. Zoological society of San Diego. Archived from the original on 2010-12-23. Retrieved 18 January 2011.
- Management of Wildlife interactions with power line networks Archived 2011-07-20 at the Wayback Machine. NamPower/NNF Strategic Partnership (2009).
- "A tree with the nesting colonies of the sociable weaver grows along D707 road in Namibia". Independent Travellers. independent-travellers.com. Retrieved December 24, 2017.
- Sociable weaver - Species text in The Atlas of Southern African Birds.
- Sociable weaver and their nests in Namibian and South Africa
- "Sociable Weaver media". Internet Bird Collection.