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Long-Term Programmes

Sociable Weaver Research Project

Project Co-ordinators

Dr Rita Covas
Dr Claire Doutrelant (CEFE-CNRS, France)

Members of the research project

Dr Sophie Lardy (Postdoctoral fellow, FitzPatrick Institute)
Dr Arnaud Tognetti (Postdoctoral fellow, IAST, France)
André Ferreira (PhD student, CIBIO, University of Porto, Portugal)
Liliana Silva (MSc student, CIBIO, University of Porto, Portugal)
Rita Fortuna (MSc student, CIBIO, University of Porto, Portugal)

Research collaborators

Dr Matthieu Paquet (University of Edinburgh, UK)
Dr Claire Spottiswoode (FitzPatrick Institute)
Prof. Ben Hatchwell (Sheffield University, UK)
Dr René van Dijk (Sheffield University, UK)
Dr Res Altwegg (Dept Statistical Sciences, UCT)
Dr Fanny Rybak (University Paris Sud, France)
Dr Bruno Faivre (University of Dijon, France)

Project overview and current directions

The sociable weaver Philetairus socius is a small southern African bird, which is remarkable for its elaborate social organisation and cooperative behaviour – from building communally one of the most remarkable structures in the bird world, to cooperatively raising young or mobbing predators. The sociable weaver research program uses an individually marked population of sociable weavers to study the evolutionary bases of cooperative behaviour and the rules that allow cooperation to persist. This is one of the longest running bird studies in Africa and our long-term data is used also to address fundamental questions about the factors driving population dynamics and predict responses to environmental change.

Current work is focusing on 1) direct fitness benefits arising from cooperation and in particular via social/sexual selection; 2) physiological costs of helping; 3) Maternal effects and manipulation of parental care (in collaboration with Matthieu Paquet, University of Edinburgh); 4) kin recognition and inbreeding avoidance (in collaboration with Ben Hatchwell and René van Dijk; 5) Factors affecting population dynamics (in collaboration with Res Altwegg, UCT).

Sociable Weaver Research Programme – Beginnings

The Sociable Weaver study was initiated in 1993 by Mark Anderson (currently executive director of Birdlife South Africa). Then an ornithologist at Northern Cape Nature Conservation and based in Kimberley, Mark was interested in getting people involved in bird ringing while collecting basic demographic data. In 1998, Rita Covas initiated a PhD project on the cooperative breeding behaviour and life history strategies of the sociable weavers through the Percy FitzPatrick Institute at the University of Cape Town. Claire Doutrelant joined the study soon after with a post-doc project and this collaboration has continued to this day. Although the study of cooperation was interrupted after Rita’s graduation in 2002, the population monitoring continued through Claire Spottiswoode’s PhD project on phenotypic and life-history differentiation among colonies. In 2008 Rita Covas and Claire Doutrelant went back to Benfontein to relaunch the research program and the project has been growing since.

Cooperation: why help?

Why do the ‘helpers’ assist other birds with their breeding attempts instead of breeding on their own? What are the benefits of this behaviour for both breeders and helpers? And what are the costs? Over the years, our research has shown that it is often the older offspring of the breeding pair that are retained as ‘helpers’. This suggests that kin selection (i.e. increasing one’s fitness indirectly by assisting the reproductive effort of close relatives) may play an important role in the evolution of this behaviour. This, however, does pre-suppose that the helpers do indeed contribute to increasing the reproductive success of the breeding pair: in the case of the weavers, this is not immediately obvious. Although our results have shown that the breeders do benefit from the presence of helpers under some conditions, this is not always the case. We have, however, shown that parents reduce their work loads when helpers are present, which may improve parental survival. We have preliminary results supporting this effect for females, but not males. This suggests that females who have helpers may in some way be able to make a ‘saving’ on their reproductive effort. As of now, the evidence points towards females decreasing their investment in producing eggs, thereby saving energy for future reproductive events and enhancing their own survival. The additional food provided to the chicks by the helpers may compensate for the smaller or poorer quality eggs.This possibility has sparked an interesting new line of research being pursued by a PhD student, Matthieu Paquet.

Cooperation and conflict

Whilst helpers may increase female survival, it appears that this does not necessarily translate into increased juvenile survival. To our great surprise, juveniles raised in the presence of helpers may be worse off than juveniles raised by pairs that lack helpers. This unexpected discovery may be a result of competition between helpers and juveniles. Because remaining in the natal colony confers several benefits, older helpers might force juveniles to disperse away from the study colonies and the study area (even though they are siblings). The possible effect of sibling competition on dispersal patterns is now being investigated.

More generally, in group-living species, where individuals collaborate in communal tasks there is also conflict around sharing the resources or workload. For example, how much effort do helpers put into their feeding effort or why do some group members obtain breeding positions while other don’t? Conflict may result in dominance hierarchies inside the group. Understanding dominance in a given society is therefore an important key to understanding conflict resolution and cooperation. Differences in resource-holding potential, aggressiveness or motivation can influence the outcome of these conflicts. Dominance hierarchies can be settled through behavioural interactions, but can also be assessed through morphological signals, providing a way to resolve contests without the costs of potential injuries. Plumage ornaments, called 'badges of status', might be used for such an assessment. These patches might evolve through intra-sexual selection (to deter rivals), social selection (e.g. to reflect dominance in a group when there is competition for resources) or sexual selection (mate choice). A new student, Margaux Rat, has now joined the project to study the role of dominance in mediating cooperation and conflict in the weavers.

Demography and population dynamics

One of the greatest benefits of long-term projects is to have variability in population parameters spanning several years and hence encompassing natural fluctuations in population trends. This provides unique opportunities to understand the factors that affect population dynamics and determine population trends. Data on the weaver population at Benfontein now span 17 years, during which time we have detected a slow but steady decrease in the population. To explore the reasons behind this trend, we collaborated with Dr Res Altwegg, a specialist researcher at SANBI. The results indicate that part of the decrease may be the result of climatic changes in the area, in particular a trend of decreasing rainfall. Decreasing numbers, whether driven by climate or not, may in itself start a snowball effect. As colony size decreases, survivorship falls and emigration rates rise: these combined responses can together result in an accelerating colony decrease. We are continuing this research to get a more detailed understanding of how different demographic parameters respond to different environmental drivers.

Another benefit of long term-studies is that one is able to follow individuals throughout their lives. This can provide insights into animal life histories that cannot be gained in any other way. By way of example, at the end of 2010 we captured two sociable weavers that had been ringed by Mark Anderson in the mid 1990s: one of these (ringed as a juvenile) was 14 years old, and the other (ringed as an adult) was at least 16 years old, making it the oldest Sociable Weaver on record.

Cooperative nest building

The massive nests of sociable weavers are believed to be built communally by all colony members, but how is this cooperation maintained? Who builds where and when and, more interestingly, how is cheating avoid? The weavers’ communal nest structure is a ‘common good’ that requires constant work to repair and enlarge. It therefore provides an ideal setting to investigate how the ‘tragedy of the commons’ can be avoided. The tragedy of the commons arises when common goods cannot be maintained because individuals acting selfishly do not contribute to the maintenance of the common good, even though in the long run everyone benefits from having it. Post-doctoral Fellow René van Dijk and Professor Ben Hatchwell from Sheffield University started working on the sociable weavers at Benfontein in 2010 with the specific objective of investigating this conundrum.

More about the team

Dr Rita Covas (CIBIO, University of Porto, Portugal and Percy FitzPatrick Institute)Rita Covas

Rita's homepage | E-mail: rita.covas@cibio.up.pt

I have a broad interest in the evolution of life history strategies and sociality in birds. My research activity focuses on two main topics: 1) the evolution of sociality and cooperative behaviour; 2) Life-history and behavioural adaptations on islands. I have used birds, and in particular the sociable weaver, to address these questions through individual-level and comparative studies. My previous research on sociable weavers has focused mostly on the costs and benefits of cooperative breeding and the genetic structure of these weavers’ society. This focus has now shifted to take a broader approach to cooperation and social behaviours in this species - both during and outside the breeding season. One of my main current interests is understanding the relative role of direct vs. indirect (kin-selected) benefits in maintaining cooperation. In addition, I am fascinated by these weavers’ flexible reproductive strategies and how reproductive investment, social factors and the unpredictable Kalahari climate determine population dynamics in this species.

My other life as a researcher investigates behavioural and life-history adaptations to insularity. Islands are simplified environments with similar characteristics, providing replicates of natural experiments in evolution that allow us a better understanding of evolutionary mechanisms. I have been investigating patterns of adaptation on islands worldwide concerning reproductive life-histories, sociality and sexual ornaments. In addition, my collaborators and I conduct a field study in São Tomé and Principe islands and nearby mainland to investigate the mechanisms underlying these adaptations.

Claire Doutrelant (CEFE-CNRS, France)

Claire's homepage | E-mail: claire.doutrelant@cefe.cnrs.fr
Claire Doutrelant

Besides understanding the costs and benefits of helping for both helpers and recipients, I am interested in the consequences of helping on individual reproductive strategies and in particular on maternal allocation to reproduction. How do parents behave in the presence of helpers? Do they modify their investment in reproduction to gain increased survival? Is there a conflict between parents and helpers and can maternal effects influence this conflict? In addition, I’m interested in establishing whether there are any direct benefits of helping and whether this might lead to conflicts between relatives around helping. This has fuelled my interest in the potential links between cooperation, signalling and social and sexual selection. Can cooperation be a signal or be used by others to get information on their cooperative propensity? Can it be a personality trait? Is this behaviour influenced by the presence of an audience?


In addition to these questions, I also work on the evolution of signals (colour and acoustic signals). For this I use long term data from both sociable weaver and blue tit coloration. More recently, I also became interested in the use of comparative approaches. Besides being interested in the functions of the signals presented by both sociable weavers and blue tits and the effect of environment on the spatio-temporal variation of the coloration, I’m interested on the evolution of female ornament and on evolution of behaviours and communication on islands.

Sophie Lardy (Postdoctoral Fellow, FitzPatrick Institute)

E-mail:sophielardy@gmail.com

Matthieu Paquet

My post-doc is focusing on the physiological cost of helping in the sociable weaver. Cooperation can only arise if benefits are greater than the costs, and across cooperative species there has been great effort to quantify the benefits, but little attention has been given to the costs. I am using both correlational and experimental approaches to investigate the costs underlying cooperative investment in nestling feeding in terms of oxidative stress, telomere length and survival.

 

 

 

 

 

Arnaud Tognetti (Institute for Advanced Study in Toulouse, IAST)

Arnaud’s homepage | Arnaud.tognetti@gmail.com

My research projects focus on the evolution of cooperative behaviour and more specifically whether cooperation can be sexually selected. Cooperation in animals has been largely explained by kin selection theory. However, the importance of direct benefits, especially the social and reproductive ones, has been overlooked. During my PhD I mainly used humans as a model species. My findings show that men are more cooperative in the presence of potential sexual partners, that women sexually prefer cooperative men and that some physical traits seem to signal men’s cooperativeness. Despite a growing evidence supporting the hypothesis that human cooperation is sexually selected, virtually no empirical studies in non-human species have been conducted. My current projects attempt to fill in this gap using the mound-building mouse (Mus spicilegus) and the sociable weaver. In the mound-building mouse, preliminary results show that females prefer males that are more cooperative in building the mound. In the sociable weaver, I am testing whether cooperation can be a signal. Notably, I am investigating whether helpers change their feeding behaviour when potential mates are around. I am conducting play-back experiments to simulate different audiences in order to test whether the helper’s behaviour change according to the sex and the identity of individuals in the audience. Finally, I am also examining the genetic underpinnings of cooperative behaviour by a candidate-gene approach. More specifically, I am testing a potential association between helping behaviour and the polymorphism of the dopamine D4 receptor (DRD4) gene.

André Ferreira (CIBIO-InBio, University of Porto)

Email: andrem343@hotmail.com

During my MSc I investigated if the sociable weaver breeders gradually transfer part of the parental care to their helpers and if this represents a cost for the nestlings. For my PhD I will focus on the role of social and sexual selection on the evolution and maintenance of cooperation. My aim is to understand if cooperative behaviour will increase the probability of mating in the future and investigate social benefits using social network analysis. I will the consistency and reliability of cooperative behaviour by investigate whether individuals invest consistently in different cooperative tasks (nest defence, nest building and feeding the chicks) and I will run personality trials (boldness, exploration and sociability) both in the wild and in captivity to test if the aptitude to cooperate is part of a behavioural syndrome.

 

 

 

 

Rita Fortuna (CIBIO-InBio, University of Porto)

Email: ritafortuna@hotmail.com

My master project aims to further assess whether sociable weaver females can use maternal effects to indirectly manipulate other individuals to provide offspring care. I’ve monitored the breeding season of several sociable weaver colonies in Kimberley, South Africa, and I’m performing video and acoustic analyses to extract correlations on the provisioning behaviour of the adult birds in relation to the offspring begging that is directed to them. I aim to understand the dissimilarities in the amount of care provided by birds with different status, paying close attention to the differences between male and female breeders and among the non-breeding cooperative individuals.

 

Liliana Silva

Email: lia_silva1973@hotmail.com

My MSc thesis focuses on the physiological costs entailed in acquisition and maintenance of dominance. I am currently investigating if there are hidden physiological challenges and higher energy expenditure associated with the frequent engagement in aggressive behaviours and dominance status maintenance. These physiological challenges may involve maintaining higher levels of stress hormones and testosterone, both related with the production of reactive oxygen species and, ultimately, with oxidative stress. I also intend to relate such costs with status signalling through plumage colour signals termed as “badge of status”.

 

 

 

Matthieu Paquet (IEB, University of Edinburgh, Scotland)

Matthieu's hompage | matthieu.paquet@outlook.com

Matthieu Paquet

I am broadly interested in behavioural ecology and more specifically in family interactions and the potential role of maternal effects as a mediator of family conflicts.

During my PhD and Post Doc with Rita Covas and Claire Doutrelant we investigated maternal effects induced by the presence of helpers and their consequences on females, males and offspring behaviour and fitness in Sociable Weavers. Among other results, we found that females laid smaller eggs containing less testosterone and corticosterone when they expected to be helped. Additionally, females’ survival increases while males’ survival decreases with the number of helpers. Finally, a cross fostering experiment revealed that chicks originating from groups with more helpers begged less than chicks from pairs without helpers early after. These results suggests that females could modulate offspring begging behaviour through maternal effects depending on breeding conditions (in this case, the presence of helpers).

I am now working on a 2 years post-doc project (Fyssen grant) in Edinburgh with Per Smiseth aiming to test the possibility that females may manipulate male parental investment through maternal effects, using the burying beetle Nicrophorus vespilloides as a model species. I co-supervise with Claire and Rita an MSc student (Rita Fortuna) who is investigating whether females modulate offspring begging behaviour in relation to the number of helpers through maternal effects.

Previous Students (last 3 years)

Kyle Lloyd: An experimental approach to assess the role of nest predation in the population dynamics of the sociable weaver (Philetairus socius) MSc, PFIAO, UCT (2016)

Margaux Rat: Dominance, social organisation and cooperation in the sociable weaver (Philetairus socius). PhD, University of Cape Town (2015)

Sofia Santos: Effects of group size on maternal allocation in a colonial cooperative breeding bird, the sociable weaver. MSc, University of Lisbon (2015)

André Ferreira: Benefits and costs of helpers: investigating the underlying mechanisms (July 2015, University of Porto). MSc, University of Porto (2015)

Matthieu Paquet: Maternal effects and life history trade-offs in a cooperative breeder, the sociable weaver (Philetairus socius). PhD, University of Montpellier (2013)

Lara Broom: The effect of helpers on the post-fledging period of a cooperatively breeding bird, the sociable weaver. MSc, University of Porto (2013)

Key co-sponsors

The DST/NRF Centre of Excellence at the Percy FitzPatrick Institute
Portuguese Science and Technology Foundation (FCT)
French Research Agency (ANR)
Marie Curie - IRSES
Natural Environment Research Council (NERC)

Sociable Weaver project publications

Paquet. M., Doutrelant, C., Loubon, M., Theron, F.,  Rat, M. and Covas, R. 2016. Communal roosting, thermoregulatory benefits and breeding group size predictability in cooperatively breeding sociable weavers. Journal of Avian Biology 47(6): 749-755.

Acker, P., Gregoire, A., Rat, M., Spottiswoode, C.N., van Dijk, R.E., Paquet, M., Kaden, J., Pradel, R., Hatchwell, B.J., Covas, R. and Doutrelant, C. 2015. Disruptive viability selection on a black plumage trait associated with dominance. Journal of Evolutionary Biology 28: 2027–2041.

Paquet, M., Doutrelant, C., Hatchwell, B.J., Spottiswoode, C.N. and Covas, R. 2015. Antagonistic effect of helpers on breeding male and female survival a cooperatively breeding bird. Journal of Animal Ecology 84: 1354–1362.

van Dijk, R.E., Covas. R/, Doutrelant. C., Spottiswoode, C.N. and Hatchwell, B.J. 2015. Fine-scale genetic structure reflects sex-specific dispersal strategies in a population of sociable weavers (Philetairus socius) Molecular Ecology 24: 4296–4311.

Paquet, M., Covas, R. and Doutrelant, C. 2015. A cross-fostering experiment reveals that prenatal environment affects begging behaviour in a cooperative breeder. Animal Behaviour 102: 251-258.

Rat, M., van Dijk, R.E., Covas, R., and Doutrelant, C. 2015. Dominance hierarchies and associated signalling in a cooperative passerine. Behavioral Ecology and Sociobiology 69: 437-448.

Altwegg, R., Doutrelant, C., Anderson, M.D., Spottiswoode, C.N. and Covas, R. 2014. Climate, social factors and research disturbance influence population dynamics in a declining sociable weaver metapopulation. Oecologia 174: 413–425

Paquet, M., Covas, R., Chastel, O., Parenteau, C. and Doutrelant, C. 2013. Maternal effects in relation to helper presence in the cooperatively breeding sociable weaver. PlosOne, 8, e59336.

van Dijk, R.E., Kaden, J.C., Argüelles-Ticó, A., Beltran, L.M., Paquet, M., Covas, R., Doutrelant, C. and Hatchwell, B.J. 2013. The thermoregulatory benefits of the communal nest of sociable weavers Philetairus socius are spatially structured within nests. Journal of Avian Biology, 44: 102–110.

Covas, R. 2012. Evolution of reproductive life histories in island birds worldwide. Proceedings of the Royal Society of London B, 279, 1531-1537. doi:10.1098/rspb.2011.1785.

Cornuau, J. H., Rat, M., Schmeller, D. S. and Loyau, A. 2012. Multiple signals in the palmate newt: ornaments help when courting. Behavioral Ecology and Sociobiology, 66(7), 1045-1055.

Doutrelant, C., Dalecky, A. and Covas, R. 2011. Age and relatedness have an interactive effect on the feeding behaviour of helpers in cooperatively breeding sociable weavers. Behaviour, 148, 1399-1417.

Covas, R., Deville, A.-S., Doutrelant, C., Spottiswoode, C.N. and Gregoire, A. 2011. The effect of helpers on the postfledging period in a cooperatively breeding bird, the sociable weaver. Animal Behavior, 81, 121-126.

Spottiswoode, C.N. 2009. Fine-scale life-history variation in sociable weavers in relation to colony size. Journal of Animal Ecology 78, 504-512.

Covas, R., du Plessis, M. and Doutrelant C. 2008. Helpers in a colonial cooperatively breeding bird help to counteract the effects of adverse breeding conditions. Behavioral Ecology and Sociobiology, 63, 103-112.

Gimenez O., Viallefont A., Charmantier A., Pradel R., Cam E., Brown C.R., Anderson M.D., Brown M.B., Covas R. and Gaillard J.-M. 2008. The risk of flawed inference in evolutionary studies when detectability is less than one. American Naturalist 172, 441–448.

Schwager, M., Covas, R., Blaum, N. and Jeltsch, F. 2008. Limitations of population models in predicting climate change effects: a simulation study of sociable weavers in southern Africa. Oikos 117:1417-1427.

Doutrelant, C. and Covas, R. 2007. Helping has signalling characteristics in a cooperatively breeding bird. Animal Behaviour. 74, 739-747.

Spottiswoode, C.N. 2007. Phenotypic sorting in morphology and reproductive investment among Sociable Weaver colonies. Oecologia 154, 589-600.

Covas, R., Dalecky, A., Caizergues, A. and Doutrelant, C. 2006. Kin associations and direct vs. indirect genetic benefits in sociable weavers Philetairus socius. Behavioral Ecology and Sociobiology, 60, 323-331.

Gimenez, O., Covas, R., Brown, C.R., Anderson, M.D., Brown, M.B. and Lenormand, T.  2006. Nonparametric estimation of natural selection on a quantitative trait using mark-recapture data. Evolution, 60, 460-466.

Covas, R. and du Plessis, M.A. 2005. The effect of helpers on artificially increased brood size in sociable weavers (Philetairus socius). Behavioral Ecology and Sociobiology, 57, 631-637.

Covas, R., Doutrelant, C. and du Plessis, M.A. 2004. Experimental evidence of a link between breeding conditions and the decision to breed or to help in a colonial cooperative bird. Proceedings of the Royal Society of London B., 271, 827-832.

Covas, R., Brown, C.R., Anderson, M.D. and Brown, M.B. 2004. Juvenile and adult survival in the sociable weaver (Philetairus socius), a southern-temperate colonial cooperative breeder in Africa. Auk, 121, 1199-1207.

Doutrelant, C., Covas, R., Caizergues, A. and du Plessis, M.A.. 2004. Unexpected sex ratio adjustment in a colonial cooperative bird: pairs with helpers produce more of the helping sex whereas pairs without helpers do not. Behavioral Ecology and Sociobiology, 56, 149-154.

Covas, R., Doutrelant, C. and Huyser, O. 2004. Nest-dependant Pigmy Falcons predate on their host, the sociable weaver. Ostrich, 75, 325-326.

Brown, C.R., Covas, R., Anderson, M.D., Bomberger Brown, M. 2003. Multistate estimates of survival and movement in the sociable weaver. Behavioral Ecology, 14, 463-471.

Covas, R., Brown, C.R., Anderson, M.D. and Bomberger Brown, M. 2002. Stabilising selection on body mass in the sociable weaver. Proceedings of the Royal Society of London B, 269, 1905-1909.