Proximate control of siblicide in cattle egrets: a test of the food-amount hypothesis

Avian sibling aggression plays an important role in controlling food distribution among nest mates. The food-amount hypothesis predicts that the amount of food obtained by siblings acts as a proximate cue controlling their level of aggression. The importance of this cue to cattle egrets (Bubulcus ibis) in Oklahoma was evaluated by studying parental feeding rates, food distribution among nestlings, and nestling aggression in three-chick broods [A-(oldest), B-, and C-chicks]. We compared nests in which siblicide occurred to nests where all three chicks survived (nonsiblicide nests). Relative to nonsiblicide nests, siblicide nests received decreasing amounts of food as the day of siblicide approached. Similarly, aggression levels of all three chicks in siblicide nests increased significantly compared with nonsiblicide nests, with most of the aggressive behavior involving B- and C-chicks. As a result, on a per-day basis, food amount and aggression exhibited a strong, negative correlation, thus providing support for the food-amount hypothesis. Though the total amount of food delivered to siblicide nests declined on the days prior to siblicide, the amount of food received by A-chicks in these nests did not. Relative to nonsiblicide nests, A-chicks in siblicide nests received an increased share (percent of volume) of the food delivered at the expense of C-chicks, with the percent remaining the same for B-chicks. The percentage of food B-chicks received the day after siblicide increased significantly from that received the day before siblicide, with no change occurring in either the amount or percentage of food received by A-chicks; clearly, B-chicks were the beneficiary of their aggressive actions that resulted in the death of C-chicks. We provide evidence supporting the hypothesis that aggression is proximately linked to food amount, possibly by a relatively simple cue such as hunger. Received: 25 November 1994/Accepted after revision: 10 February 1996     

Brood parasitism disproportionately increases nest provisioning and helper recruitment in a cooperatively breeding bird

Obligate avian brood parasites lay their eggs in nests of other species (hosts), which raise parasitic young. Parasitic nestlings are likely to influence host’s parental behaviours as they typically beg for food more vigorously than young host for a given hunger level. However, few studies have tested this idea, with conflicting results. These prior studies were largely limited to biparental hosts, but little is known about the effect of brood parasitism on parental behaviours in hosts that breed cooperatively. We followed a multimodel approach to examine the effect of brood parasitism on nest provisioning and helper recruitment in the baywing (Agelaioides badius), a cooperative breeder parasitised by screaming (Molothrus rufoaxillaris) and shiny (Molothrus bonariensis) cowbirds. Multimodel inference results indicated that feeding visits increased with nestling age, cooperative group size and number of cowbird nestlings in the brood. Brood size had little influence on feeding visits, which further suggests that baywings adjusted their provisioning effort in response to cowbird parasitism. In addition, nests parasitised artificially with shiny cowbird eggs or hatchlings recruited more helpers than unmanipulated nests having only host or screaming cowbird young. Our results provide novel evidence that brood parasitism and cooperative breeding interact in determining the levels of nest provisioning.     

A critical analysis of ‘false-feeding’ behavior in a cooperatively breeding bird: disturbance effects,satiated nestlings or deception?

‘False feeding,’ where helpers arrive at nests with food but fail to provision the young, has been reported in several cooperative species. This and other potentially ‘deceptive’ behavior has been interpreted as indicating that helping may operate as a signal within such social groups. We critically examine these phenomena in the provisioning behavior of the bell miner Manorina melanophrys. Excessively close observation distances can artificially elevate the rate of false feeding in this (and other) species, but once this had been accounted for, there was little evidence for any ‘deceptive’ behavior by helpers or breeders. Natural and experimentally induced variation in the presence of a potential conspecific audience at the nest did not have any consistent influence upon the rate of false feeds, which was low at 7.94% of 6,880 nest visits. Instead, encountering unexpectedly low levels of brood demand provided a more parsimonious explanation for those visits where helpers failed to feed nestlings or ate the food themselves. Failure to completely transfer a load to nestlings was more likely when the load contained a high proportion of sticky lerp, indicating a simple prey-transfer problem. Finally, individuals that arrived at nests without prey were often members of neighboring breeding pairs, suggesting that these few non-feeding visits may instead involve an information-gathering function. We, therefore, suggest that future studies explicitly exclude the possibility of observer disturbance and all aspects of normal provisioning behavior before applying the terms ‘false feeding’ or ‘deceptive’ and inferring anything more than straightforward helping at the nest.     

American robin nestlings compete by jockeying for position

Summary We investigated whether nestling American robins (Turdus migratorius) were capable of influencing food distribution in their nests by perceiving that certain sectors of the nest received a relatively high proportion of feedings and positioning themselves accordingly. Feeding observations were obtained from videotape recordings taken at different stages of the nestling period. Parents generally arrived at a predictable location on the nest rim and allocated proportionally more food to nestlings in the central position. The degree of nestling movement was significantly positively correlated with variation in the predictability of parental arrival locations on the nest rim. Furthermore, nestlings moved more in broods suffering brood reduction. This suggests that when competition for food is intense and the location of parental arrival is predictable, nestlings respond by jockeying for access to the most favorable (i.e., central) position in the nest. We conclude that jockeying for position by nestlings can influence the pattern of food allocation by parents, and that hungry nestlings can improve their competitive standing against nestmates by moving to positions where parents are more likely to feed them. Correspondence to: S.B. McRae     

Robin’s egg blue: does egg color influence male parental care?

A recent hypothesis suggests that birds’ blue-green egg colors may be a sexually selected signal of female (and potentially nestling) quality that males use to make parental investment decisions. While there is some empirical support for this idea, both theory and observations question its validity. To test this hypothesis experimentally, we examined the influence of egg color on male American robin Turdus migratorius behavior by replacing natural clutches with four artificial eggs that were all either pale or vividly colored, close to the extremes in natural egg coloration. At the end of the incubation period, three unrelated nestlings were fostered into each experimental nest, and parental provisioning behavior was monitored when nestlings were 3, 6, and 9 days old. Male provisioning rate for 3-day-old nestlings was significantly higher in the vivid egg treatment compared to both the pale egg treatment and untreated controls, but there was no effect of egg color on paternal behavior at the older nestling stages. Male feeding rate at unmanipulated nests was only weakly positively related to natural egg color (chroma) when nestlings were 3 days old. These results suggest that blue-green egg color may act as a post-mating signal of female quality or investment in this species, but our findings do not exclude the possibility that egg color pigmentation also serves other adaptive functions.     

Maternal effects on begging behaviour: an experimental demonstration of the effects of laying sequence, hatch order, nestling sex and brood size

Differential resource allocation by females across the laying sequence has been hypothesised as a mechanism through which females could either compensate nestlings that hatch last in asynchronous broods or promote brood reduction. In this study we artificially incubated eggs and cross-fostered offspring to manipulate nestlings’ position in the hatching order, to identify whether the competitive ability of nestlings is dependent on position in the laying sequence. In both control and experimentally reversed broods, first hatched chicks had a higher survival than last hatched siblings. Yet, nestlings that hatched from eggs laid in the second half of a clutch begged with a greater intensity than nestlings hatched from eggs laid in the first half of a clutch. In natural broods, the greater begging competitiveness of nestlings from later-laid eggs led to a moderation of sibling competition and these nestlings achieved the same body size and weight as nestlings from eggs laid in the first half of the clutch. The lack of a substantial difference in the size and condition of surviving nestlings in respect to laying order suggests that differential resource allocation across the egg-laying sequence partially compensates for hatching last in asynchronous broods and reduces the negative effects of the nestling size hierarchy. The effect of laying order, brood size and experimental treatment also differed for male and female nestlings. Our study highlights the need to be aware of the complex and subtle effects of nestling sex and laying sequence when investigating genetic and environmental influences on individual fitness.     

Nestling provisioning in polygynous great reed warblers (Acrocephalus arundinaceus): do males bring larger prey to compensate for fewer nest visits?

Most studies of social polygyny in birds have examined male provisioning on the basis of the number of feeding visits. This may be misleading if males compensate for infrequent visits by bringing larger prey at each visit. We investigated nestling provisioning in the socially polygynous great reed warbler, Acrocephalus arundinaceus, in south Central Sweden in 1996–1997. We collected data on rate of feeding visits, prey size and the amount of biomass delivered by males and females. Males had lower rates of feeding visits and provided smaller prey to nestlings in secondary than in monogamous and primary nests. Secondary females had higher rates of feeding visits and brought larger prey than monogamous and primary females. These results confirm that secondary females face a potential cost of polygyny through a lower rate of male feeding, and that this cost was reinforced by the significantly lower male provisioning rate (biomass h^–1) at secondary nests. Secondary females compensated for the lack of male assistance by increasing their rate of feeding and bringing larger prey. As a result, offspring in nests of secondary females received as much food as did those in nests of primary females. Prey load size increased with the parent’s proportion of feeding visits, suggesting that parents use different feeding strategies depending on their amount of responsibility for nestling provisioning. We suggest that parents which take the main responsibility for nestling feeding have to forage further away from the nest, and based on optimal-foraging theory, they should then on average bring larger prey to their nest. Received: 4 April 1999 / Received in revised form: 12 October 1999 / Accepted: 23 October 1999     

Reproductive enhancement by helpers and an experimental inquiry into its mechanism in the bicolored wren

Summary As part of continuing studies of sociality in the wren genus Campylorhynchus we have been studying the bicolored wren — a facultatively cooperative breeder — for the past 6 years in the central Venezuelan savanna. Reproductive groups have ranged in size from 2 to 5. In one of our study populations, only about 15% of the groups contained helpers, and nearly all these contained only a single male helper (Fig. 2). In an adjacent population, the majority of groups contained helpers, and more than half of these contained several helpers of either sex. Territory size is, on average, much smaller in the latter population. In these populations the presence of a single helper is associated with a three-fold increase in reproductive success (Table 1). Additional helpers are not associated with further reproductive enhancement. Enhancement is chiefly due to an increased proportion of nest starts that eventually produce independent juveniles. This reproductive enhancement is not merely an epiphenomenon resulting from the presence of helpers on territories which are superior for other reasons, such as greater resource availability or the quality of particular parents. It is also not a function of the mean or variance in nestling feeding rate. Predator exclusion experiments, in which certan nests were artificially protected from terrestrial predators, suggested that the mechanism of reproductive enhancement was heightened effectiveness of nest defense. Helpers are usually nondispersers from the parental territory, and have always been found to be close relative of the nestlings that they assist in rearing.     

Influence of kinship on helping behavior in Galápagos mockingbirds

Summary The social organization of the Galápagos mockingbird (Nesomimus parvulus) in unusual in that groups frequently include more than one breeding pair (plural breeding), and helping behavior is flexible: some birds neither breed nor help, while others do both. To investigate the influence of kinship on helping behavior, I categorized each bird as a helper or non-helper with respect to each nest within its group where it had an opportunity to help. The incidence of helping varied with relatedness: more birds helped when nestlings available to be fed were close relatives than when not. This result was independent of a higher incidence of helping among males than among females and of variation with age among males. Proportionally more nonbreeding than breeding males helped, but breeding and nonbreeding females helped equally infrequently; breeders helped most often after their own nests failed. The incidence of helping was highest among birds with opportunities to feed offspring of breeders that had fed the potential helper as a nestling, suggesting a mechanism for kin discrimination based on associative learning. Juveniles with opportunities to choose among alternative recipients preferentially fed closely related nestlings, but insufficient information was available to determine if adults also did so. Kinship did not influence the rate at which nestlings were fed by helpers. Juveniles fed nestlings at lower rates than did adult helpers, but helping effort was otherwise unaffected by age, sex, or relatedness. Limitation of help to former feeders functions as a mechanism for directing aid to relatives in a plural breeding system where degrees of kinship vary among potential recipients within the same group.     

Is obligate siblicidal aggression food sensitive?

In avian species whose chicks show facultative siblicide, attacks increase with food deprivation. In species that show obligate siblicide, this causal relationship is not expected, but no test has been made. When we composed artificial pairs of young brown boobies, Sula leucogaster (an obligately siblicidal species), and supplied variable amounts of food to the older nestlings in each pair, food ingestion was related to the most intense form of attack, pushes, which can cause death by expelling the broodmate from the nest. The less food an older nestling ingested, the more time it spent active and the greater its rate and absolute frequency of pushes, and the more often it expelled its nestmate. Hence, deficient food provision to older nestlings could precipitate siblicidal expulsion of broodmates. Younger nestmates were aggressive too, and the more they were pushed and expelled, the more they pecked. Aggression of senior brown-booby broodmates may be flexible and food sensitive in order to optimize the timing of siblicide or to make siblicide weakly facultative.Communicated by R. Gibson     

Chick recognition and acceptance: a weakness in magpies exploited by the parasitic great spotted cuckoo

Hosts of brood parasites have evolved the ability to discriminate non-mimetic and even mimetic eggs, but not non-mimetic chicks. Here we demonstrate that the great spotted cuckoo Clamator glandarius does not provide its magpie Pica pica host with a super-normal stimulus that helps to avoid recognition, because single cuckoo chicks introduced into otherwise unparasitized magpie nests are not fed at a higher frequency than single magpie chicks introduced to parasitized magpie nests. Another series of experiments demonstrated that magpies have the ability to discriminate cuckoo chicks, mainly when these are introduced at the end of the nestling period, and especially when the cuckoo chick together with a magpie chick is presented to adult magpies outside the nest. This supports the idea that cuckoos exploit the obligatory reaction of magpies to feed all young that have been hatched in their nests and whose signatures they have learnt. Furthermore, the experimental cuckoo chicks in parasitized magpie nests were more likely to be accepted than they were in non-parasitized nests. This supports the hypothesis that magpies may learn to recognise their own nestlings as those present in the nest and may indicate that a comparison between cuckoo and magpie nestlings is the basis of discrimination.     

Self-monitoring of reproductive success: nest switching in the redlip blenny (Pisces: Blenniidae)

Summary In the redlip blenny Ophioblennius atlanticus, commonly found on Caribbean reefs, eggs are laid in a male's nest and are guarded by the male until they hatch as planktonic larvae. Male reproductive success, defined as the number of egg batches hatched per reproductive period, was positively correlated with male size and with the inner surface area of the male's nest. Male blennies often switch nests between reproductive periods. Most nest switching (83%) occurred following periods of low reproductive success. Moreover, a male having low reproductive success was more likely to switch if the inner surface area of his nest was small. Most nest switching (72–80%) was to a nest of larger surface area than the previous nest. In 72% of all switches, males had higher reproductive success in the period following the switch than in the one preceding it. The results suggest that male redlip blennies monitor their current reproductive success and the characteristics of their current nests, switch to better nests if their reproductive success is low, and typically benefit from the decision to do so. These capabilities have seldom been demonstrated in any phylum.     

Helping at the nest,allofeeding and social status in immature arabian babblers

Summary Arabian babblers, Turdoides sqamiceps, are cooperatively breeding, group territorial birds, occurring in desert habitats. Non-breeders participate in several types of cooperative behaviour, including care of eggs, nestlings and fledglings, and bringing food to one another (allofeeding). This paper reports on observations of helping with eggs and young, and peer allofeeding, performed by immature babblers, fledged the previous season or earlier in the same season. The birds were from a babbler population studied since 1971 in the Arava valley of eastern Israel. They belonged to groups in which all individuals had been colourringed and were accustomed to human observers. Individuals and nests in the territories of these groups could be watched from distances of 1–2 m without causing alarm, so fine details of behaviour could be observed in the field. In most allofeeding interactions observed, a more dominant individual brought food to a subordinate. Sometimes the subordinate bird avoided accepting the proferred food, and was then hit or chased by the bird that had attempted to feed it. Occasionally a subordinate bird attempted to feed a more dominant individual. Dominant birds always refused to take food offered by a subordinate, and hit or chased any subordinate attempting to feed them. Frequencies of visits to nests were correlated with helper rank for those visits where the incoming bird displaced a previous visiter from the nest. Frequences of visits to unattended nests, however, were not correlated with helper rank. Similarly, frequencies of feeding visits to fledglings were correlated with helper rank until incubation of the next brood began. After this, the correlation disappeared. Numerous instances of aborted nest visits were observed in which a helper, often carrying food, arrived at the nest-tree but left again without visiting the nest. In many other cases, a helper arrived at the nest-tree but delayed visiting the nest for several minutes. Aborted and delayed visits usually occurred when a more dominant bird was in the vicinity of the nest. This suggests interference between helpers. Direct interference between helpers visiting fledglings was occasionally observed. In such cases, a more dominant helper snatched food from a subordinate approaching fledglings, and then fed this food to the fledglings itself. Interference between helpers, and conflict between proferers and recipients of food during allofeeding, are not easily explained by kin selection or reciprocity. On the other hand, such behaviour is readily explained by a hypothesis which suggests that individuals may increase their social status in the group by performing cooperative behaviour. Babblers that establish status by demonstrating ability to bear the short-term costs of cooperative behaviour, rather than through direct aggression towards rivals, are likely to forge collaborative relationships with other group members. Since babblers must collaborate to establish and defend a territory, such relationships are essential to reproductive success.     

Positive correlation between helpers at nest and nestling immune response in a cooperative breeding bird

In cooperatively breeding species, helpers may contribute to the success of the brood by increasing the number of independent offspring, but also, they may affect offspring condition and, hence, their survival and recruitment into the breeding population. This second type of benefits is rarely included in theoretical models or assessed in field studies. Immune response is a good proxy of individual quality and fitness, and there is good evidence that the performance of the immune system of chicks during the nestling phase is related to their chances of survival and future reproduction. However, no study has so far explored whether helpers at the nest might contribute to enhance immune functioning of nestlings in species with a cooperative breeding system. Here we investigate this issue in the azure-winged magpie (Cyanopica cyanus) and found for the first time a positive correlation between the number of helpers at nest and the cell-mediated immune response of nestlings. This effect was not explained by a general improvement of body condition of chicks because it was independent of individual variation in body mass or tarsus length. Our results suggest that helping can have subtle effects on the quality of offspring that may influence their survival and future reproduction.     

Fifteen-spined stickleback (Spinachia spinachia) females prefer males with more secretional threads in their nests: an honest-condition display by males

In the fifteen-spined stickleback (Spinachia spinachia), the male alone builds a nest and provides care for the eggs until they hatch. The nest is made of filamentous algae held together with shiny secretional threads of a glycoprotein, here called tangspiggin. Tangspiggin is produced by transformed kidney cells. I investigated how tangspiggin production was related to food intake by giving males low or high food rations. Males in the high-food group produced significantly more tangspiggin than those in the low-food group. Since low food rations did not lead to a significant drop in resting metabolic rate (oxygen consumption), tangspiggin production appears to be one of the first energy-demanding processes to be dropped during food deprivation. Among males given equal food rations, females preferred to mate with those with elevated levels of tangspiggin in their nests. Tangspiggin threads may signal safety for the offspring by keeping the eggs within the nest and protecting them from egg predators. Moreover, the threads become less shiny with age, due to particle deposition, and older nests that may house older (more valuable) eggs are thereby well camouflaged. Tangspiggin provides an honest signal of male condition, acting as an extra-bodily ornament, signaling direct benefits to females or possibly also indirect benefits of "good genes" from a male who is a successful forager.     

Asymmetric contests at the nest

Hatching asynchrony of nestling birds leads to weight asymmetries, which in turn affect the nestlings’ relative success when competing for feedings brought to the nest. We present a game theoretic model that predicts how weight asymmetry influences the nestlings’ energy on securing feedings, thus determining the caloric value remaining for weight gain as well as the distribution of feedings obtained. The model has a unique Evolutionary Stable Strategy (ESS) profile, in which nestlings in more asymmetric nests exhibit less aggression and hence achieve larger weight gain per feeding. The impetus for this model was data from a long-term study of Arabian babblers (Turdoides squamiceps) that showed a surprising negative correlation between the number of feedings that a nest received and the overall weight gain in the nest. This finding is, however, entirely consistent with our model—in more symmetric nests, the individuals fight more and are consequently hungrier and beg for additional food, are fed more, but still gain less weight due to the higher energetic costs of fighting. The model provides a fundamental explanation also for related findings in other species, in which chicks in asynchronous broods were found to be heavier than those from synchronous broods. In addition, it supports the sibling rivalry hypothesis by which brood asynchrony may diminish aggressive interactions among nestlings, leading to more efficient use of resources.     

The importance of nestling location for obtaining food in open cup-nests

Observations and experiments were carried out at 34 four-nestling nests of Arabian babblers (Turdoides squamiceps) and feeding events were analyzed according to hatching order and nestling location in the nest. Nestlings were fed in a negative correlation with hatching order. Nestling locations in relation to the provisioners were defined as Near, Far, Right, Left, and Center. Feeders fed closer nestlings more often than those further away, and straight ahead rather than sideways. In the open circular nest, the feeding adults' positions were unpredictable and equally distributed around the nest. Each peripheral position therefore served equally as Near, Far, Right and Left positions. The Center was independent of the arrival direction of the feeders and was advantageous relative to the peripheral positions. The importance of the central position was demonstrated by three experiments. (a) Food deprivation for 1 h caused the first-hatched nestling to occupy the center position and gain more feedings than its siblings. (b) Introduction of a Perspex barrier into the nest, thus eliminating the central position and preventing the nestlings from changing places, led to a loss of importance of hatching order and equal provisioning of the nestlings. (c) Fencing the nest so that entry was possible from only one permanent direction, resulted in the first-hatched nestling occupying the near position more often than its nestmates and obtaining 52% of the feedings provisioned to the whole brood. These findings imply that the architecture of the nest has an important role in food distribution among the nestlings, and contributes to reducing inequalities in the siblings' abilities to obtain food.     

Paternal care in the European starling,Sturnus vulgaris: nestling provisioning

The extent to which male birds in polygynous species with biparental care assist in nestling feeding often varies considerably between nests of different mating status. Both how much polygynous males assist and how they divide their effort between nests may have a profound effect on the evolution of mating systems. In this study we investigated how males in the facultatively polygynous European starling Sturnus vulgaris invested in their different nests. The amount of male assistance affected the quality of the offspring. Polygynous males invested as much as monogamous males, but divided their effort asymmetrically between nests, predominantly feeding nestlings of first-mated (primary) females. Although females partly compensated for loss of male assistance, total feeding frequency was lower at primary females’ nests than at monogamous females nests. Secondary females received even less assistance with nestling rearing, and the extent to which males assisted decreased with the length of the interval between the hatching of the primary and secondary clutches. These results are contrasted with those from a Belgian populations of starlings with a much more protracted breeding season and thus greater opportunities for males to attract additional mates during the nestling rearing period. The results show that both the “defence of male parental investment model” and the “asynchronous settlement model” have explanatory power, but that their validity depends on the potential length of the breeding season. Received: 21 July 1995/Accepted after revision: 13 July 1996     

Deception by helpers in cooperatively breeding white-winged choughs and its experimental manipulation

White-winged choughs (Corcorax melanorhamphos) are obligate cooperative breeders, living in groups which may contain up to 20 birds. Although breeding is dominated by a single pair, all birds contribute to rearing young, including the provisioning of nestlings. However, some birds which have carried food to the nest, even to the point of placing the food in the gaping mouth of a nestling, consume the food themselves rather than provision the nestlings. Birds which fail to feed nestlings are typically young, and are only likely to fail to deliver food when they cannot be observed by other group members. Birds which have just failed to deliver food are more likely to engage in alternative helping behaviours such as allopreening the nestlings than are helpers which have just delivered food in the conventional manner. Failure to deliver food is almost eliminated when foraging constraints are experimentally reduced by supplemental feeding of the group. Collectively these observations suggest that young white-winged choughs act deceptively by simulating helping behaviours without sacrificing food supplies. Received: 24 January 1997 / Accepted after revision: 6 June 1997     

Female cannibalism and male courtship tactics in threespine sticklebacks

Summary Female threespine sticklebacks (Gasterosteus aculeatus) frequently raid male nests and eat all the eggs therein. We tested the hypothesis of Vickery et al. (1988) that females prefer to raid nests containing large numbers of eggs than ones with smaller numbers of eggs. This hypothesis is based on the finding that females spawning in nests containing many eggs will have reduced hatching success because of egg crowding. By consuming the male's eggs and forcing him to rebuild his nest, raiding females might obtain a new opportunity to spawn under better conditions. Our results were consistent with the first prediction of this hypothesis that females were more likely to spawn in nests containing fewer eggs than in nests with many eggs. However, this may be the result of males becoming less receptive to females as the number of eggs in their nests increases. Prediction 2 was that females should raid those nests containing the most eggs. Contrary to this prediction, males defending only one clutch were as likely to have their nests raided by groups of females as males defending several clutches of eggs. Female cannibalism is therefore unlikely to have evolved as a means of gaining access to a male defending a small number of eggs. We also examined the tactics used by males to counter female raids. Most raids occur when the male is courting, and nests are more vulnerable to shoals of females than to single females. Therefore, we hypothesized that males with eggs preferentially court a single female rather than large groups of females, and that males without eggs court both groups indiscriminately. We also predicted that males restrict the number of females they mate with when risk of having their nest raided is high. Our results indicate that: (1) both males with eggs and those without eggs minimize the risk of female cannibalism by courting solitary females rather than groups of females and (2) males limit the number of females that lay eggs in their nest when several potentially raiding females are present. Offprint requests to: G.J. FitzGerald