Experimental Nests Research Articles

Habitat-specific clutch size and cost of incubation in eiders reconsidered

The energetic incubation constraint hypothesis (EICH) for clutch size states that birds breeding in poor habitat may free up resources for future reproduction by laying a smaller clutch. The eider (Somateria mollissima) is considered a candidate for supporting this hypothesis. Clutch size is smaller in exposed nests, presumably because of faster heat loss and higher incubation cost, and, hence, smaller optimal clutch size. However, an alternative explanation is partial predation: the first egg(s) are left unattended and vulnerable to predation, which may disproportionately affect exposed nests, so clutch size may be underestimated. We experimentally investigated whether predation on first-laid eggs in eiders depends on nest cover. We then re-evaluated how nesting habitat affects clutch size and incubation costs based on long-term data, accounting for confounding effects between habitat and individual quality. We also experimentally assessed adult survival costs of nesting in sheltered nests. The risk of egg predation in experimental nests decreased with cover. Confounding between individual and habitat quality is unlikely, as clutch size was also smaller in open nests within individuals, and early and late breeders had similar nest cover characteristics. A trade-off between clutch and female safety may explain nest cover variation, as the risk of female capture by us, mimicking predation on adults, increased with nest cover. Nest habitat had no effect on female hatching weight or weight loss, while lower temperature during incubation had an unanticipated positive relationship with hatching weight. There were no indications of elevated costs of incubating larger clutches, while clutch size and colony size were positively correlated, a pattern not predicted by the 'energetic incubation constraint' hypothesis. Differential partial clutch predation thus offers the more parsimonious explanation for clutch size variation among habitats in eiders, highlighting the need for caution when analysing fecundity and associated life-history parameters when habitat-specific rates of clutch predation occur.

Blue tits (Cyanistes caeruleus) respond to an experimental change in the aromatic plant odour composition of their nest

Although the use of olfaction by birds is now widely recognised, the olfactory abilities of passerine birds remain poorly explored, for historical reasons. Several studies however suggest that passerines can perceive volatile compounds in several biologically relevant contexts. In Corsica, recent findings suggest that cavity-nesting blue tits may use volatile compounds in the context of nest building and maintenance. Although they build their nests mainly from moss, female blue tits also frequently incorporate fragments of several species of aromatic plants in the nest cup. In field experiments, breeding female blue tits altered their nest maintenance behaviour in response to experimental addition of aromatic plants in their nest. In aviary experiments, captive male blue tits could be trained to detect lavender odour from a distance. Here I report results from a field study aimed to test whether adult blue tits altered their chick-feeding behaviour after an experimental change in nest odour composition. I experimentally added fragments of aromatic plant species that differed from those brought in the nests before the start of the experiment in a set of experimental nests and added moss, the basic nest material, in a set of control nests. Both male and female blue tits hesitated significantly longer entering the nest cavity after addition of new aromatic plant fragments, as compared to moss addition. This response was especially observed during the first visit following the experimental change in nest plant composition. Nest composition treatment had no effect on the time spent in the nest. This study demonstrates that free-ranging blue tits detect changes in nest odour from outside the nest cavity.

Experimental support for the use of egg uniformity in parasite egg discrimination by cuckoo hosts

Common cuckoo (Cuculus canorus) parasitism drastically reduces the reproductive success of their hosts and selects for host discrimination of cuckoo eggs. In a second stage of anti-parasite adaptation, once cuckoos can lay eggs that mimic those of their hosts, a high uniformity of host egg appearance within a clutch may favour cuckoo egg discrimination. Comparative evidence provides indirect support for this hypothesis although experimental support is currently lacking. Here, we studied the effect of experimentally decreased uniformity of host egg appearance on cuckoo egg discrimination by great reed warbler (Acrocephalus arundinaceus) hosts in a population in which long-term cuckoo parasitism has led to high levels of cuckoo–host egg mimesis. We manipulated host clutch uniformity by adding extra spots to fresh host eggs just after they were laid. Rejection of non-mimetic experimental eggs added to these nests was compared with those in control nests in which uniformity was not altered. Previously, by over-painting real spots in a control group of nests, we showed a negligible effect of our paints on hosts’ perception of their eggs. We show that for the great reed warbler, non-mimetic experimental eggs were relatively more tolerated in experimental nests, i.e. with lower uniformity (40%) than in control nests (5%). This is the first experimental study, to our knowledge, which demonstrates a reduced discrimination of foreign eggs as a consequence of an increase of egg phenotypes variation perception in a cuckoo host.

Egg losses and nest desertion in Greater Rheas Rhea americana

Avian nest desertion should occur when the cost of attending the nest results in a reduction of parental fitness. In Greater Rheas Rhea americana, the male incubates the eggs so that the decision to desert the nest is made exclusively by him. Because of constraints, the timing of desertion may affect the possibility of renesting. We estimated nest desertion rates through the breeding season and at different stages of the nesting cycle (laying and early, mid- and late incubation). We also analysed the effect of egg losses at different stages of the nesting cycle on the probability of deserting the nest. Nest desertion rates decline throughout the breeding season. The probability of deserting the nest was higher during the laying stage and decreased through incubation. For all stages, egg losses were higher in nests that were deserted than in nests that were still active at the end of the corresponding stage. Egg losses were less likely to elicit nest desertion as incubation advanced. Egg losses in experimental (unattended) nests were not random. We postulate that egg losses during the first stages of the nesting cycle would be a good predictor of future egg losses and risk of nest failure. As females remain associated with the male during egg-laying and because incebation in rheas is an energetically costly activity that may affect renesting attempts, early nest desertion could increase a male's ability to remate and renest.

Density-dependent effects on hatching success of the olive ridley turtle, Lepidochelys olivacea

Historically, the olive ridley arribada at Playa Nancite, Costa Rica, was one of the largest olive ridley arribadas in the eastern Pacific with 70,000 nesting females in a year. Recently the Nancite arribada drastically declined. We hypothesized that the population decline at Playa Nancite could have been due to low hatching success as a result of the high density of nests on the beach, such that recruitment to the population was insufficient to balance losses. To test this hypothesis, we examined density-dependent effects on hatching success and their underlying mechanisms by experimentally manipulating nest densities in experimental plots on the nesting beach. We set up four nest-density treatments in five experimental blocks. We measured effects of density on hatching success, CO(2) and O(2) concentrations and temperature both within nests and in sand adjacent to nests frequently during incubation. Experimental nest densities affected hatching success with the highest density having the lowest hatching success. Higher nest density led to lower O(2) levels and higher CO(2) levels in the nest with greater changes in the latter part of the incubation. Highest temperatures occurred in high-density areas. Temperatures were lower in sand surrounding the nest than in the nest. Effects of density on temperature, CO(2) and O(2) were confirmed at a naturally high-density nesting beach, Playa La Flor, Nicaragua. Long-term failure in production of hatchlings due to historic high densities may have contributed to the decline of arribadas on Playa Nancite. Thus, density-dependent population control would have operated at the embryonic life stage in this population of olive ridley turtles.

Abiotic Suitability of Recycled Glass Cullet as an Alternative Sea Turtle Nesting Substrate

Because of the myriad of environmental concerns related to critically eroded shoreline areas, recycled glass (cullet) has been postulated as a potential alternative source material for beach fill. However, the newly proposed cullet beach material must uphold the nesting incubation properties of endangered species such as sea turtles. This study is the first in which the abiotic parameters of recycled glass cullet is investigated as an alternative beach fill material in relation to the nesting habitat requirements of marine turtles. By constructing a simulated sea turtle nesting hatchery and with the use of thermal/moisture logging sensors and extracted gas probe samples, we determined that recycled cullet maintains the abiotic nesting chamber properties to allow for successful sea turtle embryo development. Simulated nests containing recycled glass cullet recorded average temperatures (27.0–31.4°C) that fell within the acceptable incubation range for sea turtles and moisture content readings that showed no significant differences from the beach sand controls (p > 0.05). Similarly, gas probe samples analyzed from all the experimental cullet nests recorded high concentrations of oxygen (≥20.0%) with no significant variations from the beach sand controls (p > 0.05). Overall, this study showed that nests constructed with a portion of recycled glass cullet offered a nesting environment equal to the developmental conditions of the native beach sand. Worldwide, the nesting beaches of sea turtles are under the constant threat of erosion, which ultimately results in the loss of nesting habitat. With this research, we document that recycled glass cullet can provide a sea turtle–friendly alternative for beach protection.

The presence of conifer resin decreases the use of the immune system in wood ants

Abstract 1. Wood ants (Formica paralugubris) incorporate large amounts of solidified conifer resin into their nest, which reduces the density of many bacteria and fungi and protects the ants against some detrimental micro‐organisms. By inducing an environment unfavourable to pathogens, the presence of resin may allow workers to reduce the use of their immune system.2. The present study tested the hypothesis that the presence of resin decreases the immune activity of wood ants. Specifically, three components of the humoral immune defences of workers kept in resin‐rich and resin‐free experimental nests (antibacterial, lytic, and prophenoloxidase activities) were compared.3. The presence of resin was associated with reduced bacterial and fungal densities in nest material and with a small decrease in worker antibacterial and lytic activities. The prophenoloxidase activity was very low in all workers and was not affected by the presence of resin.4. These results suggest that collective medication with resin reduces pathogen pressure, which in turn decreases the use of the inducible part of the immune system. More generally, the use of plant secondary compounds might be an efficient and economical way to fight pathogens.

Breeding Dispersal and Nesting Behavior of Burrowing Owls Following Experimental Nest Predation

Nest predation is considered a primary factor affecting the life-history characteristics and particularly dispersal of many avian species. We tested the hypothesis that nest predation would increase dispersal probability, dispersal distance and the frequency of renesting. We removed eggs from burrowing owl (Athene cunicularia) nests to simulate nest predation in southeastern California. Owls responded to egg removal with increased dispersal probability, nesting attempts and egg production. We found that nest predation tended to increase dispersal probability (50% depredated nests vs. 14% control nests), which occurred fairly soon after nest predation (0–25 d). Dispersal distance was highly variable among owls (range: 148–13,012 m). Following experimental nest predation, burrowing owls increased the number of nesting attempts and thus the total number of eggs produced in a season, regardless of dispersal. Clutch size, however, decreased as the number of breeding attempts increased. Despite large initial clutch size, burrowing owls in the Imperial Valley may have adapted to nest predation by both dispersal and the ability to renest frequently.

Temporal dynamics of edge effects on nest predation risk for the marbled murrelet

Habitat fragmentation can cause population declines greater than those expected from habitat loss alone. This can result from detrimental “edge effects”, which occur when predation rates are higher at habitat edges relative to interiors. The marbled murrelet ( Brachyramphus marmoratus) is a threatened seabird which nests in old-growth forests, a habitat that is being fragmented by ongoing harvest. There is little consensus on the magnitude of edge effects on marbled murrelets, or how they might vary by edge-type. We compared the fates of experimental murrelet nests at paired edge and interior locations at 52 sites in two regions of south-western British Columbia, Canada. Sites were chosen at “hard” edges (recent clearcuts), “soft” edges (regenerating forest), and natural edges (i.e., riparian areas). We used nest cameras to distinguish disturbances caused by known predators of real nests. Accounting for landscape-scale fragmentation, disturbances by avian predators were significantly more frequent at hard edges relative to interiors, but less frequent at soft edges. There were no edge effects at natural-edged sites. These results imply that detrimental edge effects adjacent to recent clearcuts may decline with time due to successional processes. Survey data suggest that this pattern was caused by Steller’s jays ( Cyanocitta stelleri), who were observed more often at hard edges than soft edges in one region. Where corvids are important predators, we recommend that managers maintain reserves that lessen the amount of hard edge per patch area. Harvest adjacent to reserves should proceed in stages to limit hard edge effects at any given time.

A flea‐induced pre‐hatching maternal effect modulates tick feeding behaviour on great tit nestlings

Summary 1A host's defence reaction against one parasite species can modulate the habitat quality for other parasites in two ways: it can provide cross-resistance against closely related species due to antigenic similarity, or it can reduce resistance to other cohabiting species, since the mounting of multiple defence reactions is more costly. 2Here we test whether two completely unrelated parasite species can influence each other across host generations, that is, whether a hen flea-induced maternal effect known to protect great tit (Parus major) nestlings against flea infestations will also alter tick (Ixodes ricinus) feeding behaviour on nestlings. 3We infested experimental great tit nests with hen fleas (Ceratophyllus gallinae) prior to egg-laying to induce the maternal effect, while all parasites were removed in control nests. Nestlings from the two types of nests were then cross-fostered into flea-free foster nests to produce broods that contained both, nestlings with and without the flea-induced maternal effect. Five days after hatching, we put five larval ticks on each nestling and assessed tick feeding behaviour. 4We found that ticks feeding on nestlings with the flea-induced maternal effect detached significantly earlier than ticks feeding on controls. The result is compatible with the hypothesis of a trans-generational parasite–parasite interaction, that is, it suggests that the flea-induced maternal effect alters tick feeding behaviour and that it may protect nestlings against tick-borne diseases by reducing tick attachment times. In addition, we found that more ticks attached on male than on female nestlings, suggesting that males are more susceptible to parasites than females as shown in other vertebrates.

Maternal attendance and the maintenance of family groups in common earwigs (Forficula auricularia): a field experiment

Abstract 1. Understanding the evolution of subsocial behaviour and parental care requires experimental tests of the functional significance of such behaviours and the role of tending parents in the maintenance of family groups. Studies in subsocial insects addressing these issues experimentally and in the field are still relatively rare.2. In such a field experiment, it is demonstrated here that the presence of tending females enhances the maintenance of family groups in common earwigs, Forficula auricularia (Dermaptera; Forficulidae). Experimental removal of tending mothers resulted in substantially decreased recovery of occupied nest burrows and larvae. This effect may have been because of decreased survival among experimental larvae, although a possible role for enhanced larval dispersal could not be fully ruled out.3. Experimental (motherless) larvae were partly observed in family groups with a tending female, in both experimental and control nest burrows, suggesting that these larvae had been adopted by family groups moving to new nest burrows, and/or that experimental larvae may have actively joined other family groups.4. This study demonstrates under field conditions the functional importance of maternal attendance for the maintenance of family groups in common earwigs, and suggests that adoption and clutch‐joining are factors affecting the social structure of this species.

Nest desertion by a cowbird host: an antiparasite behavior or a response to egg loss?

Natural selection can favor songbirds that desert nests containing eggs of the parasitic brown-headed cowbird (Molothrus ater). However, the high variability in desertion of parasitized nests within species is perplexing in light of the typically high costs of parasitism. Because nest desertion can also be a response to partial clutch predation, we first asked if Bell’s vireos (Vireo bellii) deserted nests in response to the presence of cowbird eggs (antiparasite response hypothesis) or to egg removal by predators and female cowbirds (egg predation hypothesis). Second, we asked whether variation in nest desertion was due to intrinsic differences among individuals or to variation in nest contents. We monitored a large number of nests (n ¼ 494) and performed a clutch manipulation experiment to test these hypotheses. The number of vireo eggs that remained in a nest was a strong predictor of desertion both within and among pairs. Neither the presence of a single cowbird egg, which leads to nest failure for this host, nor the number of cowbird eggs received in a vireo nest influenced nest desertion. Furthermore, vireos did not desert experimental nests when we immediately exchanged cowbird eggs for vireo eggs but deserted if we removed vireo eggs and replaced them with cowbird eggs the following morning. Desertion of parasitized nests by Bell’s vireos can be almost entirely explained as a response to partial or complete clutch loss and does not appear to have been altered by selection from brood parasitism. Key words: Bell’s vireo, brown-headed cowbird, egg predation, evolutionary lag, host‐parasite coevolution, Molothrus ater, Vireo bellii. [Behav Ecol]

First documentation of sibling cannibalism in a small passerine species

In its broadest definition, cannibalism refers to feeding on an individual of the same species. Sibling cannibalism in birds is usually ascribed to raptor species. The cannibalistic behaviour generally follows brood reduction caused by sibling competition over resources or siblicide (Ingram 1959, Bortolotti et al . 1991, Stanback & Koenig 1992, Mock & Parker 1997). It has been suggested that nestlings of nonpredatory species are incapable of feeding on a dead sibling because of physical constraints, feeding method or inclination (Stanback & Koenig 1992). Among passerines, sibling cannibalism might be expected in predatory groups such as corvids or shrikes, and it has been observed in nestlings of the Black-billed Magpie Pica pica , following aggressive behaviour and siblicide (Reynolds 1996). However, to date, there has been no evidence for sibling cannibalism in small non-predatory passerines. In this paper, we report on a female House Sparrow Passer domesticus , caught on video camera feeding her nestlings with the carcass of their dead sibling. We are unaware of any previous documentation of sibling cannibalism of this kind in a passerine species. Our observation was recorded in the course of a study on parent‐offspring communication in free-living House Sparrows during spring 2004. The Sparrows breed in nestboxes located on two large buildings on the campus of Tel-Aviv University. We used infrared video cameras to monitor parental response to 3-day-old nestlings supplemented by begging playbacks broadcast from a small speaker inside the nest. The playbacks were activated for 10 s during several parental visits; their frequency and intensity were within the natural range of Sparrow begging calls; and both parents and nestlings behaved normally during these experiments. In one of the experimental nests, the two smallest of the five nestlings died, probably due to starvation, one during the night before the experiment and the other early in the morning of the experiment (25 May 2004). Brood reduction of this magnitude is common in Sparrow nests at this

Food acquisition by common cuckoo chicks in rufous bush robin nests and the advantage of eviction behaviour

The common cuckoo, Cuculus canorus, is a brood parasite that monopolizes parental care of its host species: soon after hatching, the chicks remove the host offspring. Although cuckoo chicks trick their foster parents into providing enough food, it is unknown whether cuckoo begging behaviour represents an advantage over that of the host chicks in a hypothetical competitive scenario. We studied the feeding behaviour of rufous bush robins, Cercotrichas galactotes, when rearing their own and parasitic chicks in natural and in experimental nests where a cuckoo and a host brood were presented simultaneously to parents. In natural parasitized and nonparasitized nests, the feeding rate for cuckoo chicks did not differ from that of a single host chick of the same age, but cuckoos were fed with a different diet and with larger prey. Thus, cuckoo chicks received a similar amount of food to that received by a whole host brood. Cuckoo chicks in experimental nests did not receive a diet, prey size or feeding rate different to that received by a single host chick and thus received considerably less food than cuckoo chicks in unmanipulated nests. These results suggest that cuckoo chicks could not outcompete host chicks, at least when parasitizing this host species, and thus that their eviction behaviour is beneficial. We discuss various explanations for the inability of cuckoos to outcompete host chicks.

European starlings: nestling condition, parasites and green nest material during the breeding season

Male European starlings (Sturnus vulgaris) intermingle fresh herbs, preferably species rich in volatile compounds, into their dry nest material. In a field study, we investigated whether these herbs affect the mite and bacteria load of the nests and the condition of the nestlings either directly or via parasite control. We examined the amount of herbs and the number of plant species males carried into their nests, the variation of volatile compounds in the headspace air of the nest boxes and mite/bacteria load of the nests throughout the season. The amount of herb material and the number of plant species, the number of substances emanated by these plants and the infestation of the nests with bacteria and mites (Dermanyssus gallinae) increased with season. In a field experiment, we exchanged natural starling nests with experimental nests with or without herbs. We found that the herbs had no effect on the mites but fewer bacteria were sampled in nests with herbs than in nests without herbs. The body mass of the fledging was not related to the season or the mite/bacteria load of the nests. However, nestlings from nests with herbs fledged with higher body mass than nestlings from nests without herbs. Both bacteria and mite load were related to nestling mortality. In nests containing no herbs, the numbers of fledglings declined significantly with the increasing mite load while the mites had no effect on the number of fledglings in nests with herbs. Thus, the nest herbs counteracted the effect of the mites. In conclusion, it seems that volatile herbs can reduce bacterial but not mite infestation of the starling nests. The positive influence of herbs on nestling growth indicates that herbs either directly (perhaps as immunostimulants) improve the condition of the nestlings and help them cope with the harmful effects of mites, or they provide a nest environment beneficial for the nestlings‘ development by the reduction of germs.

Use of Radio-Telemetry to Test for Investigator Effects on Nesting Mallards, <em>Anas platyrhynchos</em>

We examined the effects of investigator activity on hatching rates of radio-marked wild female Mallards (Anas platyrhynchos), and evaluated the efficacy of radio-telemetry to minimize nest disturbance, characterize vegetation at nest sites, and mark nests for later relocation. Differences in hatching rates between birds that were flushed once (experimental) and those never flushed (control) approached significance (P = 0.086). However, hatching rates did not differ (P = 0.588) between the two groups when nests where investigator activity caused abandonment (30% of experimental nests) were removed from analysis. If the nest remained active, flushing the bird and visiting the nest once did not appear to increase the likelihood of the nest being depredated. We were able to locate 92% of radio-telemetry marked nests (control) after the female was no longer tending the nest. Radio-telemetry provides a technique to collect relatively unbiased nesting data for Mallards without disturbing the female.

An experimental study on the causes of sex‐biased mortality in the black‐headed gull − the possible role of testosterone

Summary During early development male offspring in avian species often suffer from enhanced mortality compared to female offspring. This has been attributed to different nutritional requirements, as sex‐biased mortality has been reported particularly in sexually size‐dimorphic species. However, other traits of the male phenotype, such as the embryonic hormone profile, have been suggested to contribute to this male disadvantage. In particular the negative effects of sex steroids on immune function may be causally involved. We investigated the role of testosterone in the expression of male phenotype disadvantage through an experimental reduction of the availability of testosterone receptors by in‐ovo injection of an anti‐androgen (Flutamide©). Experimental nests contained a male and a female chick hatching from control treated eggs and a male and a female chick hatching from Flutamide treated eggs. Male‐biased mortality occurred in control chicks at a stage where the sexes did not yet differ in their growth pattern, suggesting that sex‐specific nutritional requirements are not necessary for male‐biased mortality to occur. Control males and control females did not differ in their cell‐mediated immunity (CMI). This renders it unlikely that the observed skewed mortality was due to sex‐specific differences in the CMI. Treatment of the eggs with flutamide antagonistically affected males and females. Flutamide treatment positively affected male development in particular through an enhanced growth rate, indicating that testosterone is involved in the expression of the male phenotype disadvantage. Female chicks hatching from Flutamide treated eggs were disadvantaged in growth and CMI. The possible pathways of this sex‐specific effect of Flutamide are discussed with regard to differential consequences of blocking the beneficial effects of maternal androgens and the interference with the process of sexual differentiation in males.

INVASIVE SHRUBS AND SONGBIRD NESTING SUCCESS: EFFECTS OF CLIMATE VARIABILITY AND PREDATOR ABUNDANCE

Previous studies have demonstrated that songbirds often use exotic plants as nesting substrates and may suffer elevated predation rates relative to nests placed in native plants. Veeries (Catharus fuscescens) frequently build nests in an exotic shrub, Japanese barberry (Berberis thunbergii), in forests of southeastern New York State, USA. We monitored Veery nesting success over a six-year period and supplemented these observations with experimental nests to determine whether predation rates differed between nests placed on the ground, in barberry shrubs, or in alternative native substrates. Using experimental nests, we found that nests raised above the ground in either barberry or native plants survived significantly longer than ground nests, but predation did not differ between the two former sites. Similarly, Veery nests on the ground suffered higher predation rates than nests in either raised native substrates or barberry; however, despite a substantially lower daily mortality rate in barberry, the dif...

Sex-biased environmental sensitivity: natural and experimental evidence from a bird species with larger females

The larger sex is often more vulnerable, in terms of development and survival, to poor conditions during early life. Differential vulnerability has implications for parental investment strategies such as sex ratio theory. When males are larger, it is not possible to separate the effects of larger size per se and other aspects of the male phenotype on vulnerability. Furthermore, offspring competition might favor the larger sex and thereby mask intrinsic, size-related effects. We studied sex-specific mortality in a bird species with reversed size dimorphism, the great skua Stercorarius skua, under natural and experimentally created poor conditions. Small eggs from extended laying sequences were used to create poor early conditions for the offspring, which were raised as singletons. Daughters had a lower survival in all treatment groups. Survival in natural broods was additionally affected by hatch date and position. Hatch weight was not different for sons and daughters but was lower in experimental than in natural nests. In natural nests, daughters fledged 10% heavier than sons, but in experimental nests, they did not reach a higher mass. The average survival difference between sons and daughters was not increased in experimental broods. However, hatch weight had a strong sex-specific effect. Very light females never survived, and survival probability of daughters increased with increasing hatch weight. By contrast, survival of sons over the same range of hatch weights was not related to weight. These findings support the hypothesis that larger (final) size per se is related to sex-specific offspring vulnerability during early life.

Worker reproduction in the antFormica fusca

We studied the kin conflict over male parentage in the ant Formica fusca. The conflict arises because each worker and queen is most related to her own sons and is thus predicted to lay eggs. Microsatellite analysis of eggs revealed that workers laid eggs in more than half the queenright experimental nests. Nevertheless, almost exclusively diploid offspring were reared in the presence of a queen. This also occurred when worker-laid haploid male eggs were experimentally introduced in to the nests. Because our experimental setup allowed us to exclude the possibility of queen policing, we conclude that worker laid eggs are removed by other workers, either as a response to their parentage or gender. Our results suggest that worker reproduction in F. fusca is ultimately an interplay of conflicts over male parentage and sex allocation and that both worker and self policing have roles as proximate mechanisms of resolution.