Parents often face a trade-off between the quality and quantity of young produced because terminating investment in current young could result in lower survival and future reproductive success, whereas initiating new breeding attempts could result in greater production of young. In cooperatively breeding species, helpers may alleviate this trade-off by assuming the role of primary caregivers to first broods, liberating breeders to initiate subsequent breeding attempts without compromising the level of care offspring receive. Here, we investigate the occurrence and consequences of brood overlap in the cooperatively breeding pied babbler (Turdoides bicolor). Brood overlap occurred only in groups and resulted in breeders primarily investing in second broods while helpers continued to provide care to first broods, resulting in dependent young from overlapping broods being raised simultaneously. Interbrood partitioning of care during brood overlap resulted in a greater production of young per season in groups (cf., pairs) without any effect on offspring survival, thus representing a reproductive benefit of task partitioning in cooperatively breeding species. Copyright 2008, Oxford University Press.
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"The southern pied babbler is a medium-sized (70–95 g, length 26–29 cm) cooperatively breeding passerine occupying the semiarid acacia savannas of the Kalahari desert (Ridley & Raihani 2008). Groups are stable, comprising a dominant male and female and between 1 and 12 adult subordinates that help to raise young produced by the dominant pair (Ridley & Raihani 2008). Each group occupies a territory that they defend year-round from neighbouring groups (Golabek, Ridley & Radford 2012). "
[Show abstract][Hide abstract] ABSTRACT: Eavesdropping behaviour can increase the total amount of information available to an individual and therefore has the potential to provide substantial benefits. Recent research has suggested that some species are ‘information givers’, particularly social species with cooperative vigilance systems, and that these species may consequently affect community structure by influencing the behaviour and niche utilisation of other species.
Here, using behavioural observations and playback experiments, we compared the behavioural change in a solitary species (the scimitarbill) and a social species (the pied babbler), to the presence and alarm calls of one another.
Our results revealed that scimitarbills underwent significant behavioural changes in the presence of social pied babblers: they reduced their vigilance rate by over 60%, increased their foraging efficiency, and expanded their niche by moving into open habitat and excavating subterranean food items. In contrast, pied babblers – who have an effective intraspecific sentinel system - did not show significant behavioural changes to the presence or alarm calls of scimitarbills.
These results suggest that interceptive eavesdropping can provide significant benefits, influencing the behaviour and habitat utilization of eavesdropping species.
"Group size in the study period ranged from 2 to 13 (mean ± SD 6.1 ± 2.6) adults (individuals > 365 days old). Birds were sexed using DNA from blood collected when ringing (for capture details, see Radford & Ridley, 2008) using the technique described in Griffiths et al. (1998). Groups defend year-round territories (Golabek et al., 2012) and move around these as a tight unit throughout the day. "
[Show abstract][Hide abstract] ABSTRACT: Individuals of many species communicate with one another using a range of vocalisations and there is often variation in the use and structure of these calls depending on sex, status and context. In social species, two or more group members may also combine their vocalisations to produce duets or choruses. While the function of duets and the different contributions of males and females have received considerable research attention, less is known about the different calls used by group members in choruses. Southern pied babblers (Turdoides bicolor) are cooperatively breeding birds of Southern Africa that live in permanent stable groups. In addition to a variety of calls given by individuals, group members frequently combine to produce raucous choruses which include several different call types. Here we describe these different call types for the first time and explore their usage, with respect to the sex and dominance status of callers, production of the call alone or as part of a chorus, and the social context. Eight out of nine possible calls used in choruses on some occasions were found to be statistically distinct. As expected from the variation shown in individual calls, some of those call types included in choruses were sex-specific and some were used more by dominants than subordinates. Moreover, there was variation in the use of different call types as solos and within choruses, as well as their occurrence in different contexts. We discuss what might be concluded about the functions of the different call types from their patterns of usage.
"Individual behavioural variation within groups of social animals can be highly advantageous in terms of overall increase in group fitness (Oster & Wilson, 1978; Wallace , 1982). In particular, task specialization is expected to result in enhanced colony efficiency and productivity , decreased individual energy expenditure to reach a communal outcome and improved resource allocation between colony members (Wilson, 1987; Schmid-Hempel, 1991; Rypstra, 1993; Ridley & Raihani, 2008). Task specialization can take many forms, from behavioural asymmetry in task performance to strict division of labour as seen in the eusocial insects, where behaviourally or morphologically specialized castes determine the limited behavioural repertoire of individuals. "
[Show abstract][Hide abstract] ABSTRACT: Understanding the social organization of group-living organisms is crucial for the comprehension of the underlying selective mechanisms involved in the evolution of cooperation. Division of labour and caste formation is restricted to eusocial organisms, but behavioural asymmetries and reproductive skew is common in other group-living animals. Permanently, social spiders form highly related groups with reproductive skew and communal brood care. We investigated task differentiation in nonreproductive tasks in two permanently and independently derived social spider species asking the following questions: Do individual spiders vary consistently in their propensity to engage in prey attack? Are individual spiders' propensities to engage in web maintenance behaviour influenced by their previous engagement in prey attack? Interestingly, we found that both species showed some degree of task specialization, but in distinctly different ways: Stegodyphus sarasinorum showed behavioural asymmetries at the individual level, that is, individual spiders that had attacked prey once were more likely to attack prey again, independent of their body size or hunger level. In contrast, Anelosimus eximius showed no individual specialization, but showed differentiation according to instar, where adult and subadult females were more likely to engage in prey attack than were juveniles. We found no evidence for division of labour between prey attack and web maintenance. Different solutions to achieve task differentiation in prey attack for the two species studied here suggest an adaptive value of task specialization in foraging for social spiders.
Full-text · Article · Nov 2012 · Journal of Evolutionary Biology