Grey-capped social weaver
|Grey-capped social weaver|
|In Amboseli, Kenya|
The grey-capped social weaver or grey-headed social weaver (Pseudonigrita arnaudi) is a sparrow-like liver-colored bird, with a pale grey crown, a dark grey bill, a whitish eye-ring, horn-colored legs, with some black in the wing and a light terminal band in the tail, that builds roofed nests made of straws, breeds in colonies in thorny Acacia trees, and feeds in groups gathering grass seeds and insects. Male and female have near identical plumage. Recent DNA-analysis confirms it is part of the weaver family. It is found in Ethiopia, Kenya, Somalia, South Sudan, Sudan, Tanzania, and Uganda.
Taxonomy and naming
French naturalist Charles Lucien Bonaparte described the grey-capped social weaver as Nigrita arnaudi in 1850. The species is named in honor of Joseph-Pons d'Arnaud, the French explorer who collected a specimen around 1841 near Juba on the White Nile, and sent it to the French Museum of Natural History. In 1903, German zoologist Anton Reichenow assigned the species to his newly erected genus Pseudonigrita, because he considered P. arnaudi and P. cabanisi related to weaverbirds (Ploceidae), while the other species Nigrita bicolor, N. canicapillus, N. fusconota and N. luteifrons are negrofinches assigned to the estrildid finches.
Ludwig Reichenbach called it Arnauds nigrita in 1863. "Grey-capped social weaver" has been designated the official name by the International Ornithological Committee (IOC). Other common names include Masai grey-headed social weaver. In Swahili it is called korobindo kichwa-kijivu.
Based on recent DNA-analysis (which did not include P. cabanisi), the genus Pseudonigrita belongs to the group of sparrow weavers (subfamily Plocepasserinae), and is most related to Philetairus socius. This clade is sister to Plocepasser. Provided that the sister relationship between the Pseudonigrita-species is correct, the following tree expresses current insights.
Subspecies and distribution
Two subspecies of the grey-capped social weaver can be distinguished. The southerly subspecies dorsalis can be distinguished by its bluish grey instead of livery brown back.
- P. arnaudi subsp. arnaudi can be found from eastern South-Sudan and neighboring northern Uganda, around Mount Elgon, the central highlands of Kenya southwards to a strip in Tanzania between Speke Gulf (a continuation of Lake Victoria at it southeastern corner) and Mount Kilimandjaro, and a few isolated populations in the very south-west corner of Sudan (South Darfur), around Mega in southernmost Ethiopia and around Xagar in southern Somalia.
- P. arnaudi subsp. dorsalis occurs in Tanzania, in a zone between the south shore of Lake Victoria to north of Lake Malawi, and an isolated population just south of Dar es Salaam.
The species is small for a weaver with 11–12 cm (4.3–4.7 in) long, and it weighs 15–26 g (0.53–0.92 oz). It is a sparrow-like liver-colored bird, with a pale grey crown, a dark grey bill, a whitish eye-ring, horn-colored legs, with some black in the wing and a light terminal band in the for a weaver relatively short tail. The tail band is visible during flight. The cap of the adult male is almost white, that of females more light grey. Adolescents have a duller plumage, a brown bill, and the cap is light liver-colored.
Eggs are laid throughout the year, but there is a peak that enables the birds to make use of periods that food is plenty, such as between August and December in South Sudan and between March and May in eastern Africa. Three or four eggs are laid in a roofed nest, that is suspended from a thin branch an in ant-gall acacia (Vachellia drepanolobium), or another spined and ant-housing acacia. The nest consists of grass straws, and during breeding and feeding the nestlings has one downward-facing opening. Eggs are approximately 19 mm long and 14 mm in diameter, greenish, bluish or white, unadorned or with fine black or olive colored specks, more dense at thick end, or so heavily blotched that the overall color seems olive-brown or ash-grey. Both parents share breeding duty but the female about twice as often as the male, until after thirteen or fourteen days, the eggs hatch.
The grey-capped social weaver feeds on both grass seeds and insects, such as grasshoppers, beetles, termites and caterpillars. Feeding mostly takes place in groups at some distance from the colony.
Nesting, breeding and care for the young
In P. arnaudi, nests are not only used for breeding and to protect the chicks, but also for fully grown birds to sleep at night. The species builds roofed nest in thorny Acacia trees and forms colonies. One of the two entrances is closed however just before eggs are laid and opened again around the moment of fledging. Male and female share incubation duties. Adult and adolescent birds from previous broods often help in nest building and feeding the chicks. The nestlings are initially fed on a diet consisting exclusively of insects, and grass seeds are only given during the last days. Fledging occurs after about twenty days.
Nests are build hanging from thin branches, often in Vachellia drepanolobium, sometimes in other acacia species such as umbrella thorn acacia (V. tortilis), blackthorn (Senegalia mellifera) or gum acacia (S. senegal). The nests have thick walls. These are constructed from grass straws, which, in the dry climates where P. arnaudi is found, keep well for many months. Nest are often constructed with two or three side-to-side or under old nests.
In Kenya, some individuals rested in their nests year round, also outside the breeding periods, with two to five together. The immediate surroundings of the nests were generally not defended against birds from other families that nest or sleep in the same Acacia tree that houses the colony. However, birds from other trees were usually attacked when landing in the colony tree. The order in which birds are allowed to feed is according to dominance, although members from other families from the same colony where better tolerated than birds from other colonies. Aggression was rare or absent between members of the same group. The behavior of the grey-capped social weaver closely resembles that of the sociable weaver Philetairus socius.
Roofed nests, with two downward-facing nest entrances, colony nesting, and choosing a thorny nesting tree, are all considered adaptations that help limit predation. Aggregated nests, thick walls and communal sleeping are considered adaptations against the cold nights in the arid distribution area of P. arnaudi.
The grey-capped social weaver is sometimes kept and bred in captivity by hobbyists. Due to its social structure, P. arnaudi only starts breeding when in larger established groups (at least about ten pairs). It needs large and high cages, and thin branches to attach the nest and lots of suitable nesting material (grass straws) needs to be available. A specialised website suggest a ground cover of sand beneath the nesting branches, and grass elsewhere, inter-planted with a few very resistant shrubs. Adults fare well on a diet of 95% seeds and 5% insects, but during the breeding season about 20% of the food should consist of living insects, such as mealworms and small crickets. Fine stone grit and calcium sources, such as shell grit and cuttlebone, need to be provided. Due to its large demand in nesting material, excessive theft may occur if other Plocepasserinae-species are kept in the same confinement. This website also suggests to compose a group at one instance and not to introduce other birds later, particularly during breeding.
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