Social Structure and the Development of Helping Behaviour in the Bell Miner (Manorina melanophrys,Meliphagidae)

The hypothesis that bell miners (Manorina melanophrys) improve their alloparenting skills during the period spent as helpers was tested by means of comparing: a) the frequency of nestling care activities, b) the frequency of nestling attendance “mistakes”, c) the gizzard contents and items brought to nestlings, and d) interactions at the nest with the breeders, for helpers of different ages. Results show that young birds made fewer feeding visits to the nestlings and made more empty (i.e. non-feeding) visits than older helpers. The few “mistakes” detected were also made by young helpers. The proportion of food items brought to the nestlings consisting of arthropods was smaller for very young helpers (≤ 3.8 months) than for older helpers. Sexually mature helpers also had relatively more arthropods than psyllid sugary covers (a food item very easy to locate and capture) in their gizzards than immatures in winter, but this difference was marginally not significant. Young helpers must learn their place within the group hierarchy, but no clear division of labor in the alloparental activities studied was detected, which might have increased the effect of learning during the period birds spent as helpers.     

Effects of clutch size manipulations on reproductive behaviour and nesting success in the cooperatively breeding Bell Miner (Manorina melanophrys)

Summary An experimental manipulation of clutch size was carried out on a wild population of the cooperatively breeding Bell Miner (Manorina melanophrys, Meliphagidae) to assess which factor(s) limit clutch size in this species. Results provide some support for the trade-off hypothesis since there is a cost of reproduction for the breeding female in terms of loss of body mass. The breeding female performs most of the nestling care. Clutches of three eggs are also laid during the mid-breeding season which is the period most favourable for breeding (i.e. nestlings grow faster). This evidence also supports the intrabrood competition hypothesis. Clutches that have lost an egg were more likely to be deserted; this may be an antipredator strategy since partial clutch predation has been recorded in the field. Nest predation was high in this study (64.9%), suggesting that many small clutches may be a strategy to decrease the effect of nest predation on reproductive success over the whole breeding season (nest predation hypothesis). Both the trade-off hypothesis and the nest predation hypothesis may apply in this case since they are not mutually exclusive. The size of the attending group did not greatly affect reproductive success in the short term, although if both age structure and size of the group are taken into account, reproductive success can be better predicted.     

Habitat selection by a despotic passerine,the Bell Miner (Manorina melanophrys): When restoring habitat through Lantana (Lantana camara) removal is not enough

The Bell Miner (Manorina melanophrys) occurs in logged eucalypt forest in northern NSW with a dense understorey of the invasive Neotropical shrub Lantana (Lantana camara) that is used for nesting. The link between Bell Miners and Lantana is important as the birds aggressively exclude all smaller and similar‐sized birds from their colonies, reducing avian diversity in forest occupied by the species. We monitored the impact of Lantana removal on Bell Miner persistence in several plots in two logged forest sites, along with untreated control plots at one of the sites. Lantana control was successful over 7 years at both sites, with regeneration of native understorey, midstorey and canopy species compensating for the loss of live Lantana cover in the understorey. Bell Miner individuals vacated the treated plots in one site (Creek's Bend) but persisted in the control and treated plots at the second site (Toonumbar National Park). Bell Miner response was correlated with forest structure: birds vacated forest with a sparse understorey (<5 m) but dense midstorey (5–15 m) and canopy (>15 m) at Creek's Bend, but remained at the site with a dense understorey but sparse midstorey and canopy at Toonumbar. We therefore predict that forest restoration that simultaneously reduces Lantana understorey and increases midstorey density will be most successful in reducing the abundance of the despotic Bell Miner and increasing avian diversity in rehabilitated sites.     

Male-biased sex ratios in broods of the cooperatively breeding bell miner Manorina melanophrys

We examined the sex ratios of adults and nestlings in the cooperatively breeding bell miner Manorina melanophrys . Males were over-represented among helpers (mean of 6.8 male helpers per nest compared to 0.3 female helpers). 58% of nestlings sampled were identified as male using a molecular genetic marker. This was a significant departure from parity, yet the magnitude of the bias varied between years. The beneficial and male-biased nature of helping behaviour in this species and the similar size of male and female nestlings suggest the net cost of raising males is lower than the cost of raising females. Consequently, the male-biased sex ratio of nestlings we observed is consistent with the predictions of the repayment hypothesis that females may bias the production of their young towards the more helpful sex. Difficulties of generating quantitative predictions from repayment models that can be tested in the field are discussed.     

The Pattern of Helping in the Bell Miner Revisited: A Reply to Jamieson and Craig

Jamieson & Craig (1987) have argued that the feeding of nestlings by nonparental birds may simply be an unselected consequence of delayed dispersal in cooperatively breeding birds in which philopatric individuals are responding to the stimulus of begging young in their vicinity (see also Jamieson 1986, 1989). Jamieson & Craig (1990) recently criticized my attempt to examine what they describe as this “unselected” hypothesis of Williams (1966) and several selectionist (or adaptive) hypotheses for the current utility of helping behaviour in the bell miner (Manorina melanophrys) (Clarke 1989). In this paper I address specific issues raised by Jamieson & Craig (1990), especially whether the unselected hypothesis is an adequate explanation of the pattern of helping in the bell miner. I will also attempt to highlight the difficulty of formulating specific predictions from the unselected hypothesis and the apparent ease with which it can be modified to accommodate departures from its general predictions.     

Facultative control of offspring sex in the cooperatively breeding bell miner, Manorina melanophrys

The ability to alter primary sex ratios has the potential toincrease a breeding individual's fitness. This is certainlytrue in those cooperative breeders where one sex is both philopatricand helps raise future offspring of its parents. We examinedthe primary sex ratio variation in the cooperatively breedingbell miner (Manorina melanophrys) in southeastern Australiaover six breeding seasons. Male offspring are the philopatricand helping sex in this system and can increase the reproductiveoutput of their parents. Bell miners aggressively defend theirterritory from all interspecific competitors and by doing soallow food resources to dramatically increase. The increasein phytophagous Psyllidae insects (which secrete a carbohydrate-richcoating that constitutes the major component of bell miner diet)leads to a decrease in tree health, often culminating in deathof the tree. Bell miners then move as groups to new areas withlow psyllid abundance, and the cycle repeats. Using this predictabletemporal variation in food availability, we aimed to determinewhether female breeders adjusted the sex ratio of broods toproduce more of the philopatric sex when food resources werehigh and more of the dispersing sex when food resources werelow. Our results provide clear evidence for such facultativecontrol of sex ratio by female bell miners. Newly founded coloniesare characterized by low food availability and a female-biasedprimary sex ratio, whereas colonies more than 1 year old havean increased food availability and a male-biased primary sexratio. We suggest treating forces associated with resource enhancementand competition as opposing sides of a single general principleand suggest that it is necessary to view both the costs andbenefits of philopatric individuals within a variable environment.     

Fine‐scale impacts on avian biodiversity due to a despotic species,the bell miner (Manorina melanophrys)

Bell miners (Manorina melanophrys; Meliphagidae) are a highly social and very aggressive honeyeater. They are despotic and cooperate in the defence of their territories against other bird species, leading to the almost complete exclusion of other avifauna from miner‐occupied regions. This study aimed to resolve some of the fine‐scale effects of bell miner aggression on avian diversity both within and adjacent to colonies to determine the true impact of a colony on local avifaunal abundance. Three areas, distributed throughout the range of the bell miner, were surveyed across both non‐breeding and breeding seasons to assess the temporal and spatial impacts of bell miner aggression on other bird species. Bell miner colonies were found to occupy very clearly defined areas and had the expected negative impact on avian diversity within their colony. The effects of bell miner colony presence on abundance and richness of avian species were found to cease at the colony boundary, with both recovering to normal levels immediately outside the bell miner colony. Whether bell miners were breeding or not, and irrespective of the amount of vegetation coverage, bell miner colonies were found to have relatively marginal impacts on avian richness and abundance. No impact of colony presence/absence was found on the richness or abundance of the avian species that dwell in the undergrowth, with some evidence that these species were actually more common at the colony edge. Our results demonstrate that the influence of bell miner colony presence upon avian biodiversity is restricted to the confines of the colony and does not radiate outwards into the surrounding habitat. Colony presence influences, therefore, have implications when considering the impact of bell miner behaviour on the diversity of insectivorous birds and processes, most notably the propagation of Bell Miner Associated Dieback.     

Provisioning calls of the cooperatively breeding bell miner Manorina melanophrys encode sufficient information for individual discrimination

Acoustically-mediated individual discrimination has been the focus of much investigation in ornithology. For cooperatively breeding species, strong selection pressure favouring individual recognition during acts of altruism is predicted under many of the most interesting hypotheses proposed to account for helping behaviour. We investigated differences in 157 calls given by 12 different individuals as they provisioned nestlings, including both breeding and helper bell miners Manorina melanophrys (Meliphagidae), a cooperatively breeding honeyeater endemic to south-eastern Australia. Individual differences were apparent in all 15 call parameters analysed, many with a high level of repeatability. Moreover, the information capacity of mew calls allows as many as 515 different signatures to exist in the system. As many parameters showed strong sex differences, separate discriminant functions were used to predict individual identity within each sex. Five parameters were used in a function that correctly identified over 90% of female calls in both a training (n = 35) and test dataset (n = 11) not used to generate the function. Among males, a separate function used six parameters to correctly assign individual identity in 89.3% (n=84; training) and 77.8% (n=27; test) of cases. Three original parameters, including spectral and spatial characteristics, were highly correlated with functions predicting identity in both sexes. The accuracy of functions was not influenced by a signaller's sex, breeding status, or by sampling period which was spread over as much as two breeding seasons within individuals. Significant potential therefore exists for bell miners to use these simple provisioning calls in individual discrimination. If this is the case, call information also has the potential to be used by receivers as predicted by signalling hypotheses proposed to account for cooperative helping behaviour, such as the pay-to-stay and social prestige hypotheses.     

Asymmetrical competition between the bell miner (Manorina melanophrys,Meliphagidae) and other honeyeaters: evidence from Southeastern Victoria,Australia

Summary The Bell Miner (Manorina melanophrys, Meliphagidae) is a medium-sized, colonial and co-operatively breeding honeyeater. Recent works show that the Bell Miner presents clear patterns of interspecific competition involving aggressive behaviour against many honeyeaters (Meliphagidae) and other bird species (Loyn et al. 1983; Clarke 1984). Nevertheless, those works have been based on short-term (1 year or less) studies only, and none of them have studied the effect territorial defence has on Bell Miners' fitness. We show how the population of honeyeaters decreased over 7 years at the Sir Colin Mackenzie Zoological Park (Southeastern Victoria, Australia). The decrease of honeyeaters in the study site was correlated with a local increase in the Bell Miner population which has been expanding since at least 1983. This process presumably led to the spatial zonation of Bell Miners and honeyeaters observed at present, while other passerine species show no sensitivity to either the invasion of Bell Miners in the recent past or to the present spatial distribution of the Bell Miner population. Finally, we show that Bell Miner reproductive activity is not affected by their interaction with competitors, which leads us to conclude that the interaction between the Bell Miner and other honeyeaters would be better described as asymmetrical competition.     

The role of psyllids (Hemiptera: Psyllidae) and bell miners (Manorina melanophrys) in canopy dieback of Sydney blue gum (Eucalyptus saligna Sm.)

Abstract The presence of the aggressive, colony-forming honeyeater, Manorina melanophrys (bell miner), in the canopies of unhealthy eucalypts has been well reported. There is, however, some debate as to the actual mechanisms producing these unhealthy trees. To investigate further some of the processes that may be contributing to this form of canopy dieback, two field trials were carried out in Olney State Forest, near Wyong, New South Wales. The study site contained Eucalyptus saligna (Sydney blue gum) with canopy dieback and was occupied by a large colony of bell miners. Close examination of the foliage revealed a large and diverse suite of phytophagous insects, including at least 16 species of psyllid (Hemiptera: Psyllidae). In the first trial, the use of bird exclusion cages over selected branches significantly improved leaf survival compared to leaves exposed to a relatively high density of bell miners. It is proposed that colonization by bell miners may interfere with the efficacy of both other insectivorous birds (through aggressive interspecific territoriality) and the invertebrate predators and parasitoids. Interference with such regulatory factors may enable some phytophagous insect populations to rise to sustained damaging levels. In the second trial, an insecticide application combined with reduced competition from the dense understorey and neighbouring trees was required to significantly improve trunk diameter and crown condition scores. After 12 months, neither treatment, by itself, significantly improved both growth measures. Possibly both treatments were required because the E. saligna trees were suffering from another source of stress (e.g. drought) in addition to the relatively high level of insect attack.     

Complex social organization reflects genetic structure and relatedness in the cooperatively breeding bell miner, Manorina melanophrys

The cooperatively breeding bell miner, Manorina melanophrys, differs from most other cooperative breeding species in the complexity of its social system, where discrete social organization occurs on at least three levels. Microsatellite markers were used to investigate the degree of genetic structure underlying the social organization of M. melanophrys by comparing colonies, coteries and nest contingents. The genetic data confirmed behavioural observations of M. melanophrys living in male kin-based groups between which females disperse short distances to breed. Estimates of FST revealed restricted gene flow between eight colonies located within 30 km that was significantly associated with geographical distance when the two most distant colonies were included. Within a high density colony significant differences were found between coteries; analysis of the degree of relatedness between coterie members showed that this is due to related individuals associating preferentially with each other. Similarly, the contingent of individuals attending a nest were generally close relatives of the young they were aiding, supporting models invoking kin selection as the selective agency mediating helping.     

No short‐term change in avian assemblage following removal of Yellow‐throated Miner (Manorina flavigula) colonies

The overabundance of Yellow‐throated Miner (Manorina flavigula) has been shown to negatively affect the abundance and richness of small birds in areas they occupy, leading to homogenization of the avifauna across the fragmented landscape. In this study, we took advantage of a planned management cull to ask the question, does the removal of Yellow‐throated Miner colonies cause an immediate change in avian species richness and abundance? This cull was undertaken around the Bronzewing Flora and Fauna Reserve (north‐western Victoria, Australia) in order to protect a resident population of endangered Black‐eared Miner (M. melanotis) from hybridization. We conducted avian surveys along roadsides surrounding the reserve at Yellow‐throated Miner colonies (n = 6), control sites with no miners (n = 7), and where colonies were removed (n = 3). We found that the cull was followed by only a very modest increase in the species richness and abundance of small birds, with no significant effects on avian assemblage overall. This result contrasts with far more dramatic increases following culls of other species of miner. Sites where miners were removed were not depauperate of other species prior to the cull, which could have been due to a combination of proximity to refuge for small birds in a neighbouring reserve or the low numbers of miners that made up each culled colony. This study highlights that assumed effects of a management action may be highly dependent upon spatial and temporal context.     

Flexible Helping Behaviour in the Azure-Winged Magpie

Helping to rear the offspring of others may be a way for younger birds to gain access to future reproduction especially when turnover of breeding opportunities is low. However, this explanation is not applicable to cases where adults also help, or when roles shift between helpers and breeders. Over a period of 6-yr, we studied a marked population of azure-winged Magpie (Cyanopica cyanus) breeding in a non-territorial, colonial system. Magpies bred in a highly flexible cooperative system, in which individuals helped at different stages of the breeding cycle, including nest building, feeding the incubating female and feeding the young and removing the faecal sacs. On average, 50% of hatched nests were assisted by helpers-at-the-nest, and nest success appeared to be positively related to the presence of helpers. Helpers were predominantly males. Although juveniles were more likely to help, both juvenile and adult birds helped. Individual birds behaved as helpers either as a first-option or after having attempted their own breeding (second-option helpers). An individual helper may assist more than one nest during the same breeding season and in different breeding seasons. Reversals between breeder and helper roles were common in both directions, within a breeding season and between years. Helping behaviour is an option for almost any member of the colony. Therefore, hypotheses related to the enhancement of future breeding opportunities for juveniles can be discarded as general explanation of helping in this species. Although the decision to help appeared to be influenced by proximal environmental conditions hindering successful breeding, the associated benefits of helping as opposed to simply recovering for future reproduction, especially for former breeders, deserve further study.     

Effects of Conformism on the Cultural Evolution of Social Behaviour

Models of cultural evolution study how the distribution of cultural traits changes over time. The dynamics of cultural evolution strongly depends on the way these traits are transmitted between individuals by social learning. Two prominent forms of social learning are payoff-based learning (imitating others that have higher payoffs) and conformist learning (imitating locally common behaviours). How payoff-based and conformist learning affect the cultural evolution of cooperation is currently a matter of lively debate, but few studies systematically analyse the interplay of these forms of social learning. Here we perform such a study by investigating how the interaction of payoff-based and conformist learning affects the outcome of cultural evolution in three social contexts. First, we develop a simple argument that provides insights into how the outcome of cultural evolution will change when more and more conformist learning is added to payoff-based learning. In a social dilemma (e.g. a Prisoner’s Dilemma), conformism can turn cooperation into a stable equilibrium; in an evasion game (e.g. a Hawk-Dove game or a Snowdrift game) conformism tends to destabilize the polymorphic equilibrium; and in a coordination game (e.g. a Stag Hunt game), conformism changes the basin of attraction of the two equilibria. Second, we analyse a stochastic event-based model, revealing that conformism increases the speed of cultural evolution towards pure equilibria. Individual-based simulations as well as the analysis of the diffusion approximation of the stochastic model by and large confirm our findings. Third, we investigate the effect of an increasing degree of conformism on cultural group selection in a group-structured population. We conclude that, in contrast to statements in the literature, conformism hinders rather than promotes the evolution of cooperation.     

Polyandry and Reproduction in the Serpentine Leaf Miner Liriomyza trifolii (Diptera: Agromyzidae)

We investigated the hypotheses that Liriomyza trifolii is a polyandrous species and that multiple mating is required to maximize female fecundity. In addition, the hypothesis that male copulating frequency reduces female fecundity was examined. Using sterile and fertile males, we found that L. trifolii females mate more than once during their life span, and that multiple mating is required to maximize female fecundity. A similar amount of sperm was transferred during five successive male copulations with an equal insemination probability. However, the probability of reproduction failure was strongly correlated with the male copulating sequence. Moreover, the failure rate of sperm transfer was found to be 6.8%. In light of these results, possible selection pressures driving for polyandry in L. trifolii are discussed.     

Evolution of Sexual Dimorphism in the Number of Tail Vertebrae in Salamanders: Comparing Multiple Hypotheses

The evolution of sexual dimorphism is an important topic of evolutionary biology, but few studies have investigated the determinants of sexual dimorphism over broad phylogenetic scales. The number of vertebrae is a discrete character influencing multiple traits of individuals, and is particularly suitable to analyze processes determining morphological variation. We evaluated the support of multiple hypotheses concerning evolutionary processes that may cause sexual dimorphism in the number of caudal vertebrae in Urodela (tailed amphibians). We obtained counts of caudal vertebrae from >2,000 individuals representing 27 species of salamanders and newts from Europe and the Near East, and integrated these data with a molecular phylogeny and multiple information on species natural history. Per each species, we estimated sexual dimorphism in caudal vertebrae number. We then used phylogenetic least squares to relate this sexual dimorphism to natural history features (courtship complexity, body size dimorphism, sexual ornamentation, aquatic phenology) representing alternative hypotheses on processes that may explain sexual dimorphism. In 18 % of species, males had significantly more caudal vertebrae than females, while in no species did females have significantly more caudal vertebrae. Dimorphism was highest in species where males have more complex courtship behaviours, while the support of other candidate mechanisms was weak. In many species, males use the tail during courtship displays, and sexual selection probably favours tails with more vertebrae. Dimorphism for the number of tail vertebrae was unrelated to other forms of dimorphism, such as sexual ornamentation or body size differences. Multiple sexually dimorphic features may evolve independently because of the interplay between sexual selection, fecundity and natural selection.     

Prod Traces (Selenichnites) from the Middle Cambrian of Morocco,with Hypotheses on the Ethology of the Tracemaker(s)

A single bedding surface was identified along the roadside close to an important road junction at Tansikht and north of Zagora in southern Morocco. This bedding plane has concomitant interference ripples and distinct horseshoe shaped concave epirelief ichnofossils dispersed across the surface. The sandstone bed belongs to the upper middle Cambrian Azlag Formation. The Azlag Formation occurs above the Bailiella Formation, with its distinctive trilobite fauna, in this section. The traces provide evidence of the ethology of an organism that was inhabiting the shallow waters during this time. Body fossils are rarely preserved in a clastic setting. The traces, assigned to the ichnogenus Selenichnites, and the new ichnospecies, Selenichnites tesiltus, are proposed, identified, diagnosed, described and illustrated herein. Possible tracemakers and behaviors are considered.