Publications

stabilizing selection on body mass in the sociable weaver philetairus socius.	the survival of small birds is often believed to increase with increasing body mass, despite some evidence that body mass is usually maintained below the physiological maximum and that there are costs associated with high body mass, such as increased energetic expenditure and predation risk. in this study, we used an eight-year dataset to investigate survival in relation to body mass in a wild population of sociable weavers (philetairus socius), a savannah-dwelling passerine bird. we present evi ...	2002	12350252
experimental evidence of a link between breeding conditions and the decision to breed or to help in a colonial cooperative bird.	in many species mature individuals delay independent reproduction and may help others to reproduce. this behaviour is often explained through ecological constraints, although recently attention has also been paid to the variation in habitat quality. if the quality of vacant habitat influences the fitness trade-off between delaying reproduction and breeding independently, individuals should delay reproduction when conditions for breeding are poor. yet, no study has experimentally manipulated habi ...	2004	15255101
nonparametric estimation of natural selection on a quantitative trait using mark-recapture data.	assessing natural selection on a phenotypic trait in wild populations is of primary importance for evolutionary ecologists. to cope with the imperfect detection of individuals inherent to monitoring in the wild, we develop a nonparametric method for evaluating the form of natural selection on a quantitative trait using mark-recapture data. our approach uses penalized splines to achieve flexibility in exploring the form of natural selection by avoiding the need to specify an a priori parametric f ...	2006	16637491
phenotypic sorting in morphology and reproductive investment among sociable weaver colonies.	colony sizes in birds can vary by orders of magnitude within species, and many studies have shown that selection pressures differ dramatically among small and large colonies. does such selection result in phenotypic sorting at the level of individuals? this study describes inter-colony differences in morphology and reproductive investment in a population of a highly colonial, communal and sedentary african passerine bird, the sociable weaver philetairus socius. relative colony sizes were fairly ...	2007	17828609
the risk of flawed inference in evolutionary studies when detectability is less than one.	addressing evolutionary questions in the wild remains a challenge. it is best done by monitoring organisms from birth to death, which is very difficult in part because individuals may or may not be resighted or recaptured. although the issue of uncertain detection has long been acknowledged in ecology and conservation biology, in evolutionary studies of wild populations it is often assumed that detectability is perfect. we argue that this assumption may lead to flawed inference. we demonstrate t ...	2008	18657010
fine-scale life-history variation in sociable weavers in relation to colony size.	1. this study investigates the mechanistic and ecological basis of phenotypic sorting in the sociable weaver philetairus socius (latham). in this colonially and communally breeding african bird, morphology, condition, age-specific survival rates and reproductive investment vary with colony size. 2. this variation might arise from non-adaptive constraints imposed by density dependence, or from adaptive life-history responses to colony size-dependent selection pressures. to attempt to distinguish ...	2009	19054222
individual heterogeneity in studies on marked animals using numerical integration: capture-recapture mixed models.	in conservation and evolutionary ecology, quantifying and accounting for individual heterogeneity in vital rates of open populations is of particular interest. individual random effects have been used in capture-recapture models, adopting a bayesian framework with markov chain monte carlo (mcmc) to carry out estimation and inference. as an alternative, we show how numerical integration via the gauss-hermite quadrature (ghq) can be efficiently used to approximate the capture-recapture model likel ...	2010	20462110
maternal effects in relation to helper presence in the cooperatively breeding sociable weaver.	in egg laying species, breeding females may adjust the allocation of nutrients or other substances into eggs in order to maximise offspring or maternal fitness. cooperatively breeding species offer a particularly interesting context in which to study maternal allocation because helpers create predictably improved conditions during offspring development. some recent studies on cooperative species showed that females assisted by helpers produced smaller eggs, as the additional food brought by the ...	2013	23536872
maternal effects in the highly communal sociable weaver may exacerbate brood reduction and prepare offspring for a competitive social environment.	maternal effects can influence offspring phenotype with short- and long-term consequences. yet, how the social environment may influence egg composition is not well understood. here, we investigate how laying order and social environment predict maternal effects in the sociable weaver, philetairus socius, a species that lives in massive communal nests which may be occupied by only a few to 100+ individuals in a single nest. this range of social environments is associated with variation in a numb ...	2013	22948278
cooperative investment in public goods is kin directed in communal nests of social birds.	the tragedy of the commons predicts social collapse when public goods are jointly exploited by individuals attempting to maximize their fitness at the expense of other social group members. however, animal societies have evolved many times despite this vulnerability to exploitation by selfish individuals. kin selection offers a solution to this social dilemma, but in large social groups mean relatedness is often low. sociable weavers (philetairus socius) live in large colonies that share the ben ...	2014	25039999
climate, social factors and research disturbance influence population dynamics in a declining sociable weaver metapopulation.	population trends are determined by gains through reproduction and immigration, and losses through mortality and emigration. these demographic quantities and resulting population dynamics are affected by different external and internal drivers. we examined how these demographic quantities were affected by weather, research-induced disturbance, local density, colony site and year in a metapopulation of 17 sociable weaver (philetairus socius) colonies over 17 years of study (4 years for reproducti ...	2014	24072437
interspecific signalling between mutualists: food-thieving drongos use a cooperative sentinel call to manipulate foraging partners.	interspecific communication is common in nature, particularly between mutualists. however, whether signals evolved for communication with other species, or are in fact conspecific signals eavesdropped upon by partners, is often unclear. fork-tailed drongos (dicrurus adsimilis) associate with mixed-species groups and often produce true alarms at predators, whereupon associating species flee to cover, but also false alarms to steal associating species' food (kleptoparasitism). despite such decepti ...	2014	25080343
the impact of humidity on evaporative cooling in small desert birds exposed to high air temperatures.	environmental temperatures that exceed body temperature (tb) force endothermic animals to rely solely on evaporative cooling to dissipate heat. however, evaporative heat dissipation can be drastically reduced by environmental humidity, imposing a thermoregulatory challenge. the goal of this study was to investigate the effects of humidity on the thermoregulation of desert birds and to compare the sensitivity of cutaneous and respiratory evaporation to reduced vapor density gradients. rates of ev ...	2014	25461643
relatedness predicts multiple measures of investment in cooperative nest construction in sociable weavers.	although communal goods are often critical to society, they are simultaneously susceptible to exploitation and are evolutionarily stable only if mechanisms exist to curtail exploitation. mechanisms such as punishment and kin selection have been offered as general explanations for how communal resources can be maintained. evidence for these mechanisms comes largely from humans and social insects, leaving their generality in question. to assess how communal resources are maintained, we observed co ...	2015	26726282
disruptive viability selection on a black plumage trait associated with dominance.	traits used in communication, such as colour signals, are expected to have positive consequences for reproductive success, but their associations with survival are little understood. previous studies have mainly investigated linear relationships between signals and survival, but both hump-shaped and u-shaped relationships can also be predicted, depending on the main costs involved in trait expression. furthermore, few studies have taken the plasticity of signals into account in viability selecti ...	2015	26249359
fine-scale genetic structure reflects sex-specific dispersal strategies in a population of sociable weavers (philetairus socius).	dispersal is a critical driver of gene flow, with important consequences for population genetic structure, social interactions and other biological processes. limited dispersal may result in kin-structured populations in which kin selection may operate, but it may also increase the risk of kin competition and inbreeding. here, we use a combination of long-term field data and molecular genetics to examine dispersal patterns and their consequences for the population genetics of a highly social bir ...	2015	26172866
avian thermoregulation in the heat: scaling of heat tolerance and evaporative cooling capacity in three southern african arid-zone passerines.	many birds can defend body temperature (tb) far below air temperature (ta) during acute heat exposure, but relatively little is known about how avian heat tolerance and evaporative cooling capacity varies with body mass (mb), phylogeny or ecological factors. we determined maximum rates of evaporative heat dissipation and thermal end points (tb and ta associated with thermoregulatory failure) in three southern african ploceid passerines, the scaly-feathered weaver (sporopipes squamifrons, mb≈10 g ...	2015	26041032
antagonistic effect of helpers on breeding male and female survival in a cooperatively breeding bird.	1. cooperatively breeding species are typically long lived and hence, according to theory, are expected to maximize their lifetime reproductive success through maximizing survival. under these circumstances, the presence of helpers could be used to lighten the effort of current reproduction for parents to achieve higher survival. 2. in addition, individuals of different sexes and ages may follow different strategies, but whether male and female breeders and individuals of different ages benefit ...	2015	25850564
reproductive and parental behavior in taveta golden weavers (ploceus castaneiceps).	taveta golden weavers are popular in zoos, but little has been published on their reproduction, social behavior, or other aspects of their management. at disney's animal kingdom® , we have had great success with our breeding program and house a large flock in our mixed-species walk-through africa aviary and smaller groups in the off-exhibit avian research center. we conducted observations on both groups in order to document behavioral differences between the groups living under differing managem ...	2015	25728345
correction: sociable weavers increase cooperative nest construction after suffering aggression.		2016	27100873
sociable weavers increase cooperative nest construction after suffering aggression.	the major transitions in evolution rely on the formation of stable groups that are composed of previously independent units, and the stability of these groups requires both cooperation and reduced conflict. conflict over group resources may be common, as suggested by work in both cichlids and humans that has investigated how societies resolve conflict regarding investment in group resources, i.e. public goods. we investigated whether sociable weavers (philetairus socius) use aggressive behaviors ...	2016	26982704
it's cool to be dominant: social status alters short-term risks of heat stress.	climate change has the potential to trigger social change. as a first step towards understanding mechanisms determining the vulnerability of animal societies to rising temperatures, we investigated interactions between social rank and thermoregulation in three arid-zone bird species: fawn-coloured lark (mirafra africanoides, territorial); african red-eyed bulbul (pycnonotus nigricans, loosely social) and sociable weaver (philetairus socius, complex cooperative societies). we assessed relationshi ...	2017	28202587
breeding decisions and output are correlated with both temperature and rainfall in an arid-region passerine, the sociable weaver.	animal reproductive cycles are commonly triggered by environmental cues of favourable breeding conditions. in arid environments, rainfall may be the most conspicuous cue, but the effects on reproduction of the high inter- and intra-annual variation in temperature remain poorly understood, despite being relevant to the current context of global warming. here, we conducted a multiyear examination of the relationships between a suite of measures of temperature and rainfall, and the onset and length ...	2017	28989782
faunal input at host plants: can camel thorn trees use nutrients imported by resident sociable weavers?	"islands of fertility" result from the focussing of water and nutrients around many shrub or tree species due to plants foraging for resources. plant-animal feedbacks may amplify the development of such islands through environmental modification due to, for example, faunal deposition of nutrients and seeds. fauna residing within vegetation clumps are likely to exert stronger feedbacks on their hosts than itinerant species. we studied the interaction between camel thorn trees (vachellia erioloba) ...	2020	33144990
how to make methodological decisions when inferring social networks.	social network analyses allow studying the processes underlying the associations between individuals and the consequences of those associations. constructing and analyzing social networks can be challenging, especially when designing new studies as researchers are confronted with decisions about how to collect data and construct networks, and the answers are not always straightforward. the current lack of guidance on building a social network for a new study system might lead researchers to try ...	2020	32953051