The Southern Pied-babbler (Turdoides bicolor) is a species of bird in the Timaliidae family. It is found in Botswana, Namibia, South Africa, and Zimbabwe. Its natural habitat is dry savanna.

Species description

The southern pied babbler is a medium-sized (75-95 g) cooperatively breeding passerine. Groups range in size from 2-16 adults. The species is sexually monomorphic, with males and females indistinguishable from physical characteristics. Each group comprises a dominant breeding pair that monopolise access to breeding opportunities. Occasional mixed parentage has been observed, but genetic analyses are required to determine to what extent subordinate group members gain parentage. All group members cooperate to help raise the young from a single clutch. Clutch size varies between 2 and 5, with a modal clutch size of three. Cooperative behaviours include: provisioning young (both in the nest and post-fledging), sentinel behaviour, territory border defense, teaching behaviour and babysitting behaviour (where semi-independent fledglings follow adults between foraging sites and away from predators). The breeding season extends from late-September to early April, although this varies between years and is strongly rain-dependent. Groups can raise up to three successful clutches per breeding season. Average incubation time is 14 days, and average time between hatching and fledging is 16 days. Fledging time varies according to group size: small groups tend to fledge their young earlier than large groups . Post-fledging, young are poorly mobile, unable to fly, and rely entirely on adult group members for food. Fledgling foraging efficiency develops slowly, and fledglings can continue to be provisioned by adults for up to four months post-fledging. The amount of care that young receive during this stage has long-term effects: fledglings that receive care for the longest periods tend to be heavier and better foragers than their counterparts. In addition, they are more likely to successfully disperse from their natal group and consequently begin reproducing earlier than their 'failed-disperser' counterparts .

Behaviour

Aggression toward fledglings is most commonly observed when the dominant pair have begun to incubate another brood. During this period, begging fledglings will be punished by parents using aggressive behaviour such as jumping on the youngster . In all cases, fledglings stop begging immediately following attack. Brood overlap results in a distinctive division of labour, with subordinate adults continuing to care for fledglings while the dominant pair concentrate their effort on the new brood. Owing to the extended period of post-fledging care in this species, this can result in dependent young from multiple broods being raised simultaneously.

Pied babblers are strongly territorial, and defend their borders using wing and vocal displays on a near daily basis. These fights rarely lead to physical aggression and injury from such fights is very rare.

Research on pied babblers has provided the first ever evidence of teaching behaviour in an avian species . Pied babblers teach their young by giving a specific purr call each time they deliver food. Young learn to associate this call with food and reach out of the nest each time they hear it. Adults exploit this association to encourage young to fledge by giving the purr call at a distance from the nest, enticing young to follow them . Post-fledging, adults continue to use the call to encourage young to move between foraging areas or away from predators. This call is also used to recruit independent fledglings to a rich foraging site , and may thus provide young with information on where to forage to locate rich food sources.

Interspecific interactions

Pied babblers have a complex interspecific interaction with the kleptoparasitic fork-tailed drongo, Dicrurus adsimilis. Drongos perch above and follow babbler groups between foraging sites and give alarm calls each time a predator is seen. When drongos are present, babblers invest less time in sentinel behaviour. However, drongos occasionally give false alarm calls and then swoop down to steal the food items that the foraging babblers have dropped upon hearing an alarm call. To avoid the cost of kleptoparasitism, large babbler groups, which have enough group members to participate in sentinel behaviour, do not tolerate drongos and aggressively chase them away from the group. Consequently, they suffer very few losses to kleptoarasitic attack. However, small groups do not have enough group members to provide sentinel behaviour without affecting time invested in other behaviours such as foraging or provisioning young. These groups therefore tolerate occasional kleptoparasitic attacks in return for the sentinel duties that drongos provide