Helper Contributions Research Articles

Helpers don't help when it's hot in a cooperatively breeding bird, the Southern Pied Babbler.

Cooperative breeding, where more than two individuals invest in rearing a single brood, occurs in many bird species globally and often contributes to improved breeding outcomes. However, high temperatures are associated with poor breeding outcomes in many species, including cooperative species. We used data collected over three austral summer breeding seasons to investigate the contribution that helpers make to daytime incubation in a cooperatively breeding species, the Southern Pied Babbler Turdoides bicolor, and the ways in which their contribution is influenced by temperature. Helpers spent a significantly higher percentage of their time foraging (41.8 ± 13.7%) and a significantly lower percentage of their time incubating (18.5 ± 18.8%) than members of the breeding pair (31.3 ± 11% foraging and 37.4 ± 15.7% incubating). In groups with only one helper, the helper's contribution to incubation was similar to that of breeders. However, helpers in larger groups contributed less to incubation, individually, with some individuals investing no time in incubation on a given observation day. Helpers significantly decrease their investment in incubation on hot days (>35.5°C), while breeders tend to maintain incubation effort as temperatures increase. Our results demonstrate that pied babblers share the workload of incubation unequally between breeders and helpers, and this inequity is more pronounced during hot weather. These results may help to explain why recent studies have found that larger group size does not buffer against the impacts of high temperatures in this and other cooperatively breeding species.

Inter-sexual differences in contributions of helpers in a tropical population of the cooperatively breeding Grey-crowned Babbler Pomatostomus temporalis

ABSTRACT The Grey-crowned Babbler Pomatostomus temporalis is a group-living, cooperatively breeding species in which offspring of both sexes are equally philopatric, but only male helpers inherit the natal territory. We quantified helping efforts in a tropical population of the babbler, and tested the hypothesis that inter-sexual differences in helping efforts are related to the chance of inheriting their natal territory. We found that the total nest visiting rate during the nestling period and fledging success were higher among larger groups, but dominant birds (breeders) did not decrease their effort with group size. The total nest visiting rate during the nestling period increased with the number of female helpers, and fledging success was higher in groups with a female-biased sex ratio. In contradiction of the above hypothesis, female helpers contributed more towards nestling care than male helpers, although the latter contributed more towards nest building. There was no tendency for helpers to contribute more care towards nestlings of related breeders than those of unrelated breeders, suggesting that indirect (kin selection) benefits for helpers may be less important than direct benefits in explaining helping behaviour in this population. Our study suggests there may be sex-specific differences in the costs and benefits of helping behaviour.

Group size increases inequality in cooperative behaviour.

In cooperatively breeding species where rearing effort is shared among multiple group members, increases in group size typically reduce average per capita contributions to offspring care by all group members (load-lightening) but it is not known how changes in group size affect the distribution of workload among group members. The socioeconomic collective action theory suggests that, in larger groups, the incentives for free riding are stronger, leading to greater inequalities in work division among group members. Here, we use the Gini index to measure inequality at the group level in the contributions of helpers to three different cooperative behaviours (babysitting, pup-provisioning and raised guarding) in groups of varying size in wild Kalahari meerkats (Suricata suricatta). In larger groups, inequality in helpers' contributions to cooperative activities and the frequency of free riding both increased. Elevated levels of inequality were generated partly as a result of increased differences in contributions to cooperative activities between helpers in different sex and age categories in larger groups. After controlling for the positive effect of group size on total provisioning, increasing levels of inequality in contributions were associated with reductions in total pup-provisioning conducted by the group. Reductions in total pup-provisioning were, in turn, associated with reductions in the growth and survival of pups (but pup growth and survival were not directly affected by inequality in provisioning). Our results support the prediction of collective action theory described above and show how the Gini index can be used to investigate the distribution of cooperative behaviour within the group.

Social contributions to the foraging behavior of young wild golden lion tamarins (Leontopithecus rosalia): Age-related changes and partner preferences.

In cooperatively breeding species, group members other than the parents contribute to the care of the young. The costs and benefits to caregiving may vary with the type of care provided and with caregiver characteristics such as age, sex, reproductive status, and foraging ability. Here I examine the relative contributions of parents, helpers and same-aged twins to the foraging and feeding activities of the young in a longitudinal study of wild golden lion tamarins, specifically with regard to direct food transfer, tolerance for coforaging or cofeeding by immatures and signaling young as to the location of profitable prey-foraging sites. I found that the type of food-related assistance varied as a function of the age of the immature and among group members. Rates of food transfer steadily declined as immatures aged, while coforaging rates peaked when juveniles were in the middle age group. Mothers and fathers were the most generous in terms of providing food to begging young. Mothers most often directed juveniles to productive foraging sites, and female helpers never did. Older siblings did not vary caregiving effort according to sex or age. Adult and subadult foraging ability was not a strong predictor of the rates at which prey was given to the young or the rates at which caregivers tolerated coforaging by immatures on plant and prey resources. Thus, foraging ability did not appreciably influence generosity to or tolerance of the young.

How do helpers help? Helper contributions throughout the nesting cycle in the cooperatively breeding brown-headed nuthatch

Breeder investment in offspring reflects a trade-off between the benefits realized from current reproductive efforts and the benefits expected from future reproductive opportunities. When assisted by nonbreeding helpers that provide care for offspring, breeders may modify reproductive investments to minimize the costs of producing offspring, or in ways that maximize productivity and offspring survival. How helpers assist breeders can vary with different stages of reproduction, and how breeders alter investment in response to helpers may change depending on the stage of reproduction. We assessed how helpers contribute to reproduction and how breeders alter their investment in response to helper contributions in the cooperatively breeding brown-headed nuthatch (Sitta pusilla). We assessed helper contributions across three stages of reproduction: (1) nest excavation, (2) maternal egg production, and (3) nestling care and development at days 8–12 post-hatching, a period of rapid nestling growth. We also investigated how breeders responded to helper contributions and the relationship of helper behavior with breeders’ reproductive success. Helpers contributed to offspring care but not nest excavation. Breeders assisted by helpers did not alter investments in nest excavation, offspring production, or offspring care. As a result, offspring raised by cooperative groups received more food and weighed more. Nests with helpers were more likely to fledge at least one offspring, even when considering variation in territory characteristics and breeder experience. Results indicate breeders likely benefit from the favorable breeding conditions helpers provided for current breeding efforts, which influenced the quality of offspring produced and their likelihood of fledging in this study. Helpers may contribute to breeders’ reproductive effort during many stages of reproduction. The presence of nonbreeding helpers should therefore influence the investments made by breeders during different stages of breeding. Investment decisions in one stage should furthermore influence later investment decisions. We demonstrated that helpers assisted breeders primarily during the offspring rearing stage in brown-headed nuthatches (Sitta pusilla), a facultative cooperative breeder. Breeders with helpers maintained their level of investments in offspring similar to the investments documented for breeders without helpers. As a result, chicks in nests with helpers received more food and were heavier, and adults with helpers were more likely to fledge at least one young. Our results suggest that the combined effects of parental and helper investment provided benefits for current broods with potentially important survival consequences for offspring.

Maternal allocation in eggs when counting on helpers in a cooperatively breeding bird

For cooperatively breeding birds, it has been proposed that breeders should reduce their investment in eggs when they count on helpers, because this can be compensated for by helpers provisioning of nestlings. Data from some species have supported this prediction, but this is not the case in others. It has also been proposed that mothers should not reduce but rather increase investment if the presence of helpers enhances the reproductive value of offspring, a pattern that might also influence egg production as long as helpers are predictable for laying females. Here, we studied maternal expenditure in eggs and clutches in the Iberian magpie, to see whether mothers reduce their expenditure at the egg stage in the presence of helpers. Our results show that investment in clutches varied depending on the year, date in the season and age of the mother, but there were no reductions in maternal expenditure per individual egg when they counted on helpers. On the contrary, a pattern emerged in the opposite direction of more investment in eggs associated with the future presence of helpers at the nestling stage. Our data suggest that the predictability of helpers, along with the type of benefits accrued from the contribution of helpers, may be crucial to understanding the reaction of mothers at egg production.

Differences in cooperative behavior among Damaraland mole rats are consequences of an age-related polyethism

In many cooperative breeders, the contributions of helpers to cooperative activities change with age, resulting in age-related polyethisms. In contrast, some studies of social mole rats (including naked mole rats, Heterocephalus glaber, and Damaraland mole rats, Fukomys damarensis) suggest that individual differences in cooperative behavior are the result of divergent developmental pathways, leading to discrete and permanent functional categories of helpers that resemble the caste systems found in eusocial insects. Here we show that, in Damaraland mole rats, individual contributions to cooperative behavior increase with age and are higher in fast-growing individuals. Individual contributions to different cooperative tasks are intercorrelated and repeatability of cooperative behavior is similar to that found in other cooperatively breeding vertebrates. Our data provide no evidence that nonreproductive individuals show divergent developmental pathways or specialize in particular tasks. Instead of representing a caste system, variation in the behavior of nonreproductive individuals in Damaraland mole rats closely resembles that found in other cooperatively breeding mammals and appears to be a consequence of age-related polyethism.

Variation in helper effort among cooperatively breeding bird species is consistent with Hamilton's Rule.

Investment by helpers in cooperative breeding systems is extremely variable among species, but this variation is currently unexplained. Inclusive fitness theory predicts that, all else being equal, cooperative investment should correlate positively with the relatedness of helpers to the recipients of their care. We test this prediction in a comparative analysis of helper investment in 36 cooperatively breeding bird species. We show that species-specific helper contributions to cooperative brood care increase as the mean relatedness between helpers and recipients increases. Helper contributions are also related to the sex ratio of helpers, but neither group size nor the proportion of nests with helpers influence helper effort. Our findings support the hypothesis that variation in helping behaviour among cooperatively breeding birds is consistent with Hamilton's rule, indicating a key role for kin selection in the evolution of cooperative investment in social birds.

No Evidence for Enforced Alloparental Care in a Cooperatively Breeding Parrot

AbstractIn cooperatively breeding species, in which non‐breeding helpers assist in rearing the offspring of breeding individuals, conflicts of interest commonly occur between breeders and helpers over their respective contributions to offspring care. During such conflicts, breeders might use aggressive behavior to enforce contributions of helpers to offspring care, especially if helpers are not related to the breeders and their offspring and thus do not stand to gain indirect fitness benefits by helping. Using a combination of behavioral and genetic data, we investigated in the cooperatively breeding El Oro parakeet Pyrrhura orcesi (i) whether breeders are commonly dominant over helpers, (ii) whether they use aggressive behavior toward helpers to enforce offspring provisioning, and (iii) whether the relatedness of helpers to the nestlings affects the frequency of—or the reaction of helpers to—such aggressions. Even though breeders were generally dominant over helpers, we found no evidence for the enforcement of alloparental care. This finding was independent of the relatedness between helpers and nestlings, even though distantly related helpers overall contributed little to offspring care. We suggest that the inability of breeders to properly assess the work rates of their helpers at least partly explains the absence of enforcement. More generally, our results add to a body of evidence suggesting that enforcement might be an exceptional rather than a general mechanism underlying the expression of alloparental care in cooperatively breeding species.

Helper effects in the azure‐winged magpie Cyanopica cyana in relation to highly‐clumped nesting pattern and high frequency of conspecific nest‐raiding

In avian cooperative breeding systems, many benefits obtained by social pairs from the presence of helpers have been uncovered. However, until now, the factors that determine the type of assistance helpers provide and the responses of social pairs have not been well illustrated. We examined the contribution of helpers to cooperative groups and the relevant responses of dominant pairs in the azure‐winged magpie Cyanapica cyana which breeds on the Tibetan Plateau. We used the capture–mark–recapture method to identify helpers. Results showed that helpers were mostly the yearling sons of dominant pairs. They mainly contributed to the cooperative group in three ways, courtship‐feeding the incubation female, provisioning the brood, and defending the nest. For responses of dominant pairs, we unexpectedly found that clutch size was not influenced by the presence of helpers at the nest. However, cooperative groups had higher brood feeding rates than biparental nests and their feeding pattern also differed to that of the latter. Consequently, nestlings in cooperative groups had larger fledging body mass than that in biparental nests. By examining reasons for nest failure, we revealed that conspecific nest‐raiding contributed to more nest failure than any other natural predators. Because of the contribution of helpers in defending against both predators and conspecific nest‐raiders, cooperative groups had higher survival rate than biparental nests. Thus, our findings suggest that in a highly‐clumped nesting pattern, factors concerning the risk of nest predation, rather than that influencing food supply, play an important role in determining helper effects and responses of aided dominant pairs.

Maternal allocation in cooperative breeders: should mothers match or compensate for expected helper contributions?

Among species with variable numbers of individuals contributing to offspring care, an individual's investment strategy should depend upon both the size of the breeding group and the relative contributions of each carer. Existing theoretical work on carer investment rules has, however, largely focused on biparental care, and on modelling offspring provisioning in isolation from other stages of investment. Consequently, there has been little exploration of how maternal investment prior to birth might be expected to influence carer provisioning decisions after birth, and how these should be modified by the number of carers present. In particular, it is unclear whether mothers should increase or decrease their investment in each offspring under favourable rearing conditions, and whether this differs under alternative assumptions about the consequences of being ‘high quality’ at birth. We develop a game-theoretical model of cooperative care that incorporates female control of prebirth investment, and allow increased maternal investment to either substitute for later investment (giving offspring a ‘head start’) or raise the value of later investment (a ‘silver spoon’). We show that mothers reduce prebirth investment under better rearing conditions (more helpers) when investment is substitutable, leading to concealed helper effects. In contrast, when maternal prebirth investment primes offspring to benefit more from postbirth care, mothers should take advantage of good care environments by investing more in offspring both before and after birth. These results provide novel mechanisms to explain contrasting patterns of maternal investment across cooperative breeders.

Helper effects on breeder allocations to direct care

Mothers receive childcare and productive assistance from allomaternal helpers in many societies. Although much effort has been aimed toward showing helper effects on maternal reproductive success, less has been directed toward highlighting the full range of potential effects on breeder behavior. I present a model of optimal maternal care with helpers, and tests of derived hypotheses with data collected among the Karo Batak-a group of Indonesian agriculturalists. To test the model's predictions I compared the effect of women receiving help from patrilateral versus matrilateral kin because those kin may provide help with different maternal responsibilities. The model predicts a decrease in maternal allocation to care that is substitutable with the helper contribution and the helper assists with that type of care; it predicts an increase in care that is nonsubstitutable with the helper contribution or substitutable care when the helper assists with other responsibilities. With the exception of one other, most models have failed to account for an increase. Analyses of time spent carrying children supported the model. With matrilateral helpers, women increased carrying; with patrilateral helpers, they decreased it. Time spent farmworking showed the opposite pattern, suggesting that matrilateral helpers effectively decrease costs, nudging optimal maternal care upward. Patterns of breastfeeding provided little support for the model. The results do, however, suggest potential proximate mechanisms by which helpers influence maternal reproductive success in cooperative breeding societies.

Food Sharing in Lion Tamarins (Leontopithecus chrysomelas): Does Foraging Difficulty Affect Investment in Young by Breeders and Helpers?

Food sharing with immatures is an important and relatively well studied aspect of infant care in many cooperative species. A key point that has not yet been fully addressed, however, is how increasing the difficulty of obtaining food influences the willingness of breeders and helpers to provision immature offspring. We used captive golden headed lion tamarins (Leontopithecus chrysomelas) to examine how breeders and helpers differ in provisioning juvenile individuals according to the level of difficulty of obtaining food. The level of difficulty in obtaining food was varied by placing the food inside tubes that allowed access only by adults. When food acquisition became more difficult, food sharing with juveniles and breeding females increased significantly. Begging calls by breeding females and juveniles increased during the experimental condition, which probably led to increases in food sharing. Breeders and helpers did not differ in their contribution to provisioning when food was easily available, nor did they differ in their contribution when food was difficult to obtain. Breeding males in callitrichids have a prominent role in transferring food to offspring, but contrary to our expectations, they did not increase food transfer in the experimental condition. An unexpected result was the increased investment of the breeding female into her current offspring when the level of difficulty of obtaining food was higher. We suggest that breeding lion tamarin females are not as constrained by reproductive costs as breeding females of other callitrichids. Degree of reproductive skew is hypothesized as a factor affecting the contribution of breeders and helpers to offspring care in cooperative breeding mammals, though we suggest that more studies are needed to validate such a generalization.

Females increase reproductive investment in response to helper‐mediated improvements in allo‐feeding, nest survival, nestling provisioning and post‐fledging survival in the Karoo scrub‐robinCercotrichas coryphaeus

In many cooperatively‐breeding species, the presence of one or more helpers improves the reproductive performance of the breeding pair receiving help. Helper contributions can take many different forms, including allo‐feeding, offspring provisioning, and offspring guarding or defence. Yet, most studies have focussed on single forms of helper contribution, particularly offspring provisioning, and few have evaluated the relative importance of a broader range of helper contributions to group reproductive performance. We examined helper contributions to multiple components of breeding performance in the Karoo scrub‐robinCercotrichas coryphaeus, a facultative cooperative breeder. We also tested a prediction of increased female investment in reproduction when helpers improve conditions for rearing young. Helpers assisted the breeding male in allo‐feeding the incubating female, increasing allo‐feeding rates. Greater allo‐feeding correlated with greater female nest attentiveness during incubation. Nest predation was substantially lower among pairs breeding with a helper, resulting in a 74% increase in the probability of nest survival. Helper contributions to offspring provisioning increased nestling feeding rates, resulting in a reduced incidence of nestling starvation and increased nestling mass. Nestling mass had a strong, positive effect on post‐fledging survival. Controlling for female age and habitat effects, annual production of fledged young was 130% greater among pairs breeding with a helper, and was influenced most strongly by helper correlates with nest survival, despite important helper effects on offspring provisioning. Females breeding with a helper increased clutch size, supporting the prediction of increased female investment in reproduction in response to helper benefits.

Individual Differences in the Helping Behaviors of Cooperatively Breeding Rufous Vangas

The Rufous Vanga breeds cooperatively, with pairs accompanied by one or more helper males. Although the contribution of helpers may be considerable, helping does not enhance reproductive success. In this study, we investigated individual differences in helping behavior and discuss the adaptive significance of helping. Contributions by helpers were very low during the nest building and incubation stages, but were greater during the nestling stage. In the first half of the nestling stage, both one-year-old and older helpers contributed less than breeders, with one-year-old helpers feeding nestlings less frequently than older helpers. However, the contribution of helpers increased during the second half of the nestling stage, while that of breeding females decreased. Both provisioning frequency and the size of food items carried by one-year-old helpers reached the same level of older helpers during the second half of the nestling stage. One-year-old sons of breeding females contributed more than unrelated helpers, however relatedness did not influence significantly the contribution of older helpers. Contribution to provisioning by one-year-old helpers did not influence their fate in subsequent years. Our data did not reveal any direct fitness benefits gained by helping at the nest for one-year-old helpers, but suggested that they helped their mothers in order to gain indirect fitness benefits through lightening their mothers labor. Older helpers may have gained direct fitness benefits through advertising to an unrelated breeding female or by feeding their extra-pair fertilized off-spring.

Helper contributions to antiparasite behavior in the cooperatively breeding bell miner

Cooperatively breeding bell miners (Manorina melanophrys) have numerous male helpers assisting at multiple nests. Helpers are often related to the brood they aid, consistent with kin selection. However, there are also unrelated helpers for which other direct fitness benefits are likely to accrue. Bell miner nestlings can become infested by the larvae of a parasitic fly (Passeromyia indecora), which reduce growth and can be fatal. We investigated the amount of time that breeding pairs and helpers closely inspected nests and preened nestlings, behaviors apparently directed at detecting and removing parasites, a form of helping previously unstudied in a cooperative bird. Female breeders provided the greatest antiparasite effort, with breeding males and helpers not differing in effort regardless of their relatedness to the breeding female or brood. We also experimentally infested nests with nonparasitic flies and larvae. All individuals removed the introduced “parasites” if and when they encountered them. Compared with control sessions, inspection effort increased for all birds immediately after the experimental infestations, but only for a short, 5-min period. Further, we detected no changes in helper antiparasite behaviors after the temporary experimental removal of either breeding females or males. Such consistent helping behavior, independent of relatedness and potential audience effects, suggests that antiparasite behavior in bell miners is not particularly kin directed or operating as a signal of helper quality. Our results instead suggest that helper antiparasite effort appears to represent adaptive investment in the welfare of the brood, consistent with direct fitness benefits from group augmentation.

Counting the costs: the evolution of male-biased care in the cooperatively breeding banded mongoose

In cooperatively breeding vertebrate societies, male and female helpers commonly vary in how much they invest in cooperative activities. Most explanations for this phenomenon centre on sex differences in the fitness benefits that helpers accrue through providing care, and few studies have explored how sex differences in the costs of helping are likely to influence how much care males and females provide. I investigated helper contributions in the banded mongoose, Mungos mungo, and asked whether differences in the way that helping trades off against male and female reproductive success can explain sex biases in helping effort. Contributions to the two main pup care activities were strongly male biased, and helping resulted in both sexes losing weight in the short term. This weight loss is unlikely to reduce the breeding success of males, as, although heavy males are more likely to gain access to oestrous females, any weight lost through helping can be regained before the next oestrous event. Furthermore, males less than 2 years old rarely gain access to oestrous females regardless of their body weight. Short-term reductions in body weight are likely to be more costly for females as the helping period coincides with conception and gestation of the next litter, and weight loss at this time is likely to reduce their probability of breeding successfully. These results suggest that male-biased care in this species has arisen because males and females differ in the way that helping trades off against their reproductive success.

Factors affecting offspring survival and development in a cooperative bird: social, maternal and environmental effects

1. In many noncooperative vertebrates, maternal effects commonly influence offspring survival and development. In cooperative vertebrates, where multiple adults help to raise young from a single brood, social effects may reduce or replace maternal effects on offspring. 2. Factors affecting offspring survival and development at different stages (fledging, nutritional independence and adulthood) were tested in the cooperatively breeding Arabian babbler to determine the relative importance of social, maternal and environmental factors at each stage. An influence of maternal effects was found during the nestling stage only. 3. Social factors affected the survival and development of young at all stages. The amount of food received from helpers influenced post-fledging weight gain, development of foraging skills, and survival to reproductive age. Environmental effects were also important, with groups occupying high-quality territories more likely to produce young that survived to maturity. 4. The strong influence of helper contributions on the survival and development of young at all stages from hatching to maturity suggests social factors may have important long-term effects on offspring fitness in cooperative societies. Traditional measures of offspring survival in cooperative birds, which commonly measure survival to fledging age only, may underestimate the significant benefit of helper contributions on the survival and development of young.

Female‐Biased Helping in a Cooperatively Breeding Bird: Female Benefits or Male Costs?

AbstractThere is often a sex bias in helping effort in cooperatively breeding species with both male and female helpers, and yet this phenomenon is still poorly understood. Although sex‐biased helping is often assumed to be correlated with sex‐specific benefits, sex‐specific costs could also be responsible for sex‐biased helping. Cooperatively breeding brown jays (Cyanocorax morio) in Monteverde, Costa Rica have helpers of both sexes and dispersal is male‐biased, a rare reversal of the female‐biased dispersal pattern often seen in birds. We quantified helper contributions to nestling care and analyzed whether there was sex‐biased helping and if so, whether it was correlated with known benefits derived via helping. Brown jay helpers provided over 70% of all nestling feedings, but they did not appear to decrease the workload of breeders across the range of observed group sizes. Female helpers fed nestlings and engaged in vigilance at significantly higher levels than male helpers. Nonetheless, female helpers did not appear to gain direct benefits, either through current reproduction or group augmentation, or indirect fitness benefits from helping during the nestling stage. While it is possible that females could be accruing subtle future direct benefits such as breeding experience or alliance formation from helping, future studies should focus on whether the observed sex bias in helping is because males decrease their care relative to females in order to pursue extra‐territorial forays. Explanations for sex‐biased helping in cooperative breeders are proving to be as varied as those proposed for helping behavior in general, suggesting that it will often be necessary to quantify a wide range of benefits and costs when seeking explanations for sex‐biased helping.

Meerkat helpers do not specialize in particular activities

Differences in the relative contributions of individual helpers to cooperative activities in vertebrate societies are sometimes interpreted as evidence of functional specialization and have been compared with the incipient subcaste systems found in some social insects. However, it is not yet clear whether some helpers specialize in particular tasks throughout their life span or whether variation in cooperative behaviour represents a temporary, age-related polyethism. We describe the development of cooperative behaviour in female helpers in meerkats, Suricata suricatta, an obligately cooperative mammal where young produced by the dominant female are reared by up to 30 helpers. Using a combination of field experiments and long-term records of the development of individuals, we investigated whether particular helpers specialize in particular activities. In the first year of life, variation in body weight affected overall levels of involvement in cooperative behaviour as well as relative contributions to different activities, generating contrasting activity profiles between light and heavy helpers. However, the effects of body weight disappeared by the second year of life, and individual differences in foraging success became the principal factor affecting contributions to cooperative behaviour. Contributions to different cooperative activities were positively correlated across individuals, with some helpers consistently contributing more than others to all cooperative activities. Our study provides no evidence that meerkat helpers specialize in particular cooperative activities.