Ecological constraints on independent nesting in facultatively eusocial hover wasps

Recent field experiments suggest that cooperative breeding in vertebrates can be driven by a shortage of breeding territories. We did analogous experiments on facultatively eusocial hover wasps (Stenogastrinae: Liostenogaster flavolineata). We provided nesting opportunities by removing residents from 39 nests within a large aggregation (1995), and by glueing 20 nests obtained from a distant site into a second aggregation (1996). We prevented nest-less floaters from competing for these opportunities in 1995 but not in 1996. In both years, helpers in unmanipulated groups were given opportunities to nest independently without having to incur nest-building costs and with a reduced wait before potential helpers emerged. Helpers visited the nests we provided, but adopted only a small proportion (5% of 111 vacancies created in 1995). Others were adopted by floaters, but a significant proportion of nests were never adopted (nine out of 20 in 1995, seven out of 20 in 1996). Helpers that visited nests did not originate from particular kinds of social group. Nests containing older brood were more likely to be adopted, and adopting females rarely destroyed older brood. A general feature of social insect but not vertebrate life-histories, the long period of offspring dependency relative to the short life expectancy of adult carers, may be a key factor constraining independent nesting.     

Behavioural and hormonal effects of social isolation and neophobia in a gregarious bird species, the European starling (Sturnus vulgaris)

Separating gregarious individuals from their group members often results in behavioural and physiological changes, like increased levels of corticosterone. Testosterone and corticosterone, in particular, have been implicated in the response of mammals to novelty. Data in birds are, however, rare. The presence or absence of group members may also influence an individual's response to novel stimuli. We assessed the behaviour and hormonal response of European starlings (Sturnus vulgaris) to a novel object in two different situations and seasons: each starling was tested when separated and when in contact with its group members in May/June (breeding season) and again in September/October (non-breeding season). Starlings are gregarious throughout the year, but as foraging flocks are small during the breeding season and large during the non-breeding season, we assumed that non-breeding starlings would be more affected by social isolation. Overall, starlings had higher levels of corticosterone, lost more body mass, and were more active when they were separated from their group. Isolated individuals, however, did not show a greater neophobic response than individuals in the presence of their group members in either season. Circulating levels of testosterone and corticosterone were higher after a test with novel object than after a test with only the familiar feeding dish in both sexes and seasons. However, control tests for handling effects confirmed only the increase in testosterone. Our study shows that social isolation is stressful for unrelated and unpaired members of a wild flocking bird species and demonstrates that novelty can lead to a rise in testosterone in birds.     

The Social System of a Communal Breeder,the Bay-winged Cowbird Molothrus badius

Molothrus badius (bay-winged cowbird), an icterine blackbird with cooperative breeding, shares behavioural and ecological characteristics with other communal nesters: it is sedentary, has a high annual survival rate (76.2%) and a strong nest-site tenacity (mean breeding dispersal of 41.9 and 89.4 m for males and females). Behavioural data, including collective agonistic displays, suggest group territoriality. Before egg hatching most breeders occurred as single pairs showing territorial behaviour (82% of nests), and nesting was usually solitary (distances to nearest nests of 25–103 m). Most breeders were apparently monogamous, with a 2.5% incidence of extrapair copulations in the territory during clutch formation. During the nestling stage one to four helpers occurred at 95% of M. badius nests. Most helpers were 1–2 years old, but older breeding adults (mostly males) that failed to rear their own offspring helped at the end of the season. The number of helpers increased (up to 4) with nestling age. Helpers were also recruited during the postfledging period, and group size reached up to 10 adults at this stage. Helpers mobbed predators and brood parasites, and provided 35% of the nestling food. Provisioning rate was positively and significantly correlated with number of helpers, although age of nestlings was the best predictor of overall food delivery rate. The helping system was almost obligate and productivity comparisons between nests with/without helpers are not possible. Data suggest that helpers increased the breeding success per nest. The correlation between the provisioning rates of parents and helpers was negative but non-significant. In 18% of nests 3 to 4 individuals were present before the nestling period, including cases of apparently polyandrous trios and one case of joint nesting by two pairs. Within Brown 's (1987) categories of social organization M. badius is mainly group territorial with plural nesting. Habitat requirements of M. badius are wide and nest sites do not appear to limit breeding. Kinship plays a role in the social system, as 9 of 12 helpers marked as nestlings helped their parents.     

Grooming relationships between breeding females and adult group members in cooperatively breeding moustached tamarins (Saguinus mystax)

Grooming is the most common form of affiliative behavior in primates that apart from hygienic and hedonistic benefits offers important social benefits for the performing individuals. This study examined grooming behavior in a cooperatively breeding primate species, characterized by single female breeding per group, polyandrous matings, dizygotic twinning, delayed offspring dispersal, and intensive helping behavior. In this system, breeding females profit from the presence of helpers but also helpers profit from staying in a group and assisting in infant care due to the accumulation of direct and indirect fitness benefits. We examined grooming relationships of breeding females with three classes of partners (breeding males, potentially breeding males, (sub)adult non-breeding offspring) during three reproductive phases (post-partum ovarian inactivity, ovarian activity, pregnancy) in two groups of wild moustached tamarins (Saguinus mystax). We investigated whether grooming can be used to regulate group size by either "pay-for-help" or "pay-to-stay" mechanisms. Grooming of breeding females with breeding males and non-breeding offspring was more intense and more balanced than with potentially breeding males, and most grooming occurred during the breeding females' pregnancies. Grooming was skewed toward more investment by the breeding females with breeding males during the phases of ovarian activity, and with potentially breeding males during pregnancies. Our results suggest that grooming might be a mechanism used by female moustached tamarins to induce mate association with the breeding male, and to induce certain individuals to stay in the group and help with infant care.     

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

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

Complex sex allocation in the laughing kookaburra

In groups of the cooperatively breeding laughing kookaburra(Dacelo novaeguineae), offspring sex varied with the type ofsocial group and with hatch rank. Groups with female helpers,especially if all helpers were female, had male-biased clutchand fledging sex ratios. Groups without female helpers (unassistedpairs or male-only helpers) had female-biased clutch and fledgingsex ratios. Breeding females responded facultatively to increasesin the number of female helpers in their group by producingmore male eggs. These biases may occur if breeding femalestry to limit the number of daughters recruited into their groupbecause unlike male helpers, female helpers depress the breedingsuccess of their parents. Across all nests, two-thirds of first-hatchedyoung were male, two-thirds of second-hatched young were female, and the sex ratio of third-hatched young was even. Hatch ranksex ratios also varied dramatically between different typesof social groups, from 16.7% for second-hatched nestlings ofunassisted pairs to 100% for first-hatched nestlings of groupswith only female helpers. A corollary of the relationship betweenhatch rank and sex was that hatching sex sequences were distributed nonrandomly: all groups avoided hatching a daughter first followedby a son (FM). Sibling competition is aggressive and sometimesfatal. Since females grow to be 15% larger than males the hatchingsequence of sexes could affect nestling growth and mortality.However, an exhaustive analysis found little evidence thatgrowth or survival of males was compromised if hatched aftera sister. The small number of FM sequences may only have occurredin nests that were able to ameliorate any negative consequences.Alternatively, when clutch size is small and fledging successunpredictable because of brood reduction, the preferred broodsex ratio may be contingent on the number of fledged young,making it advantageous to order the sexes in the brood.     

Group structure, mating system and extra-group paternity in the co-operatively breeding White-breasted Thrasher Ramphocinclus brachyurus

Avian co-operative breeders show a diverse range of social and reproductive systems. Here we combined microsatellite genotyping with field observations over three consecutive breeding seasons to investigate the social structure and mating system of the White-breasted Thrasher Ramphocinclus brachyurus . Co-operative breeding was facultative in this species, with approximately one-third of nests having helpers. Breeding groups comprised a pair of breeding adults and up to three helpers of either sex. Within co-operative groups, age was associated with parentage in both sexes. Helpers were retained offspring and either rarely or never achieved parentage in current broods. There was no evidence of egg dumping and a relatively small percentage of chicks (7.5%, n  = 67) were fathered by males from outside the co-operative group. The White-breasted Thrasher is a globally Endangered species with a very small and declining population. A captive breeding programme for this species is not recommended at present, but may become necessary in the future, and any such programme should take account of our findings regarding breeding behaviour and group structure.     

Genetic analysis reveals diverse kin‐directed routes to helping in the rifleman Acanthisitta chloris

The social organization of cooperatively breeding species is extremely variable, with diverse social group composition and patterns of relatedness. Species that exhibit alternative routes to helping within the same population are potentially useful systems to investigate the causes and fitness consequences of diverse evolutionary pathways to cooperative behaviour. In this study, we use microsatellite markers and field observations to describe helping behaviour and patterns of relatedness in the unusual cooperative breeding system of the rifleman Acanthisitta chloris. First, we show that rifleman helpers consist of a remarkably diverse demographic, including males and females, who may be adult or juvenile, failed breeders or nonbreeders, or even successful breeders that simultaneously feed their own brood. Adult helpers mostly helped at first‐brood nests, while first‐brood juveniles assisted their parents at second broods. Second, we show that rifleman pairs are strictly sexually monogamous, and helpers did not gain any current reproductive success through helping. Third, genotyping showed that contrary to previous assumptions, helpers were closely related to the recipients of their care and preferentially directed care towards relatives over contemporaneous nests of nonrelatives. Finally, we show that variation in helper provisioning effort was attributed to age: juvenile helpers provisioned less than adults and were less responsive to the demands of a growing brood. Overall, our results show that the diverse routes to helping in this unusual species are driven by the common theme of kinship between helper and recipients, resulting in a previously underestimated potential for helpers to gain indirect fitness benefits.     

Fitness consequences of helping behavior in the western bluebird

We examined the fitness consequences of helping behavior inthe western bluebird (Sialia mexicana) at Hastings Reservationin Carmel Valley, California, USA, and tested hypotheses forhow helpers benefit from engaging in alloparental behavior.Both juvenile and adult western bluebirds occasionally helpat the nest During a 12 year period, all adult helpers and mostjuvenile helpers were male. Helpers usually fed at nests ofboth their parents and rarely helped when only one parent waspresent. The frequency of pairs with adult helpers was only7%, but nearly one-third of adult males helped among those withboth parents on the study area. At least 28% were breeders whosenests failed. The propensity to help appears to depend uponparental survival, male philopatry, and the breeding successof potential helpers. Feeding rates were not increased at nestswith juvenile helpers, apparendy because breeding males reducedtheir feeding rates. In contrast, adult helpers increased theoverall rates of food delivery to the nest in spite of a reductionin the number of feeding trips made by both male and femaleparents. Helpers did not derive any obvious direct fitness benefitsfrom helping, but they had greater indirect fitness than nonhelpersdue to increases in nestling growth rates and fledging successat their parents' nests. Helpers fledged fewer offspring intheir first nests than did nonhelpers, suggesting that theywere birds with reduced reproductive potential. Although wehave not yet measured the effect of extrapair fertilizationson the fitness benefits of helping, we calculated the differencein fitness between helpers and nonhelpers as a function of thepotential helper's paternity when breeding independently andhis father's paternity in the nest at which he might help. Inconjunction with constraints on breeding and indirect fitnessbenefits, we predict that relatedness of males to the youngin their own as well as their parents' nests will influencehelping behavior in western bluebirds.     

Extrapair paternity, inclusive fitness, and within-group benefits of helping in western bluebirds

In central coastal California, USA, 3–16% of western bluebird ( Sialia mexicana ) pairs have adult male helpers at the nest. Demographic data on a colour-ringed population over a 13-year period indicate that helpers gain a small indirect fitness benefit through increases in the number of young fledged from nests of close kin. A small proportion of adult helpers (16%) that were able to breed and help simultaneously had higher annual inclusive fitness than males that only bred. These males comprised such a minor proportion of helpers that the mean fitness of helpers was still lower than the mean fitness of independent breeders. We used DNA fingerprinting to determine whether extrapair fertilizations alter within-group benefits enough to tip the balance in favour of helping behaviour. Overall, 19% of 207 offspring were sired by males other than their social father and extrapair fertilizations occurred in 45% of 51 nests. Intraspecific brood parasitism was rare so that mean mother-nestling relatedness approximated the expected value of 0.5. Extrapair paternity reduced putative father-offspring relatedness to 0.38. Mean helper-nestling relatedness was 0.41 for helpers assisting one or both parents and 0.28 for helpers aiding their brothers. Helpers rarely sired offspring in the nests at which they helped. Helping was not conditional on paternity and helpers were not significantly more closely related to offspring in their parents' nests than to offspring in their own nests. Although helpers may derive extracurricular benefits if helping increases their own or their father's opportunities for extrapair fertilizations, within-nest inclusive fitness benefits of helping do not compensate males for failing to breed. Breeding failure and constraints on breeding are the most likely explanations for why most helpers help.     

Building multiple nests is associated with reduced breeding performance in a south temperate population of Grass Wrens Cistothorus platensis platensis

Grass Wrens Cistothorus platensis build two types of non-breeding nest structures: platforms and dummy nests. Platforms are rudimentary accumulations of grasses concealed between vegetation. Dummy and breeding nests are dome-shaped with a similar structural layer. We used a nest-removal experiment and observational data to evaluate several hypotheses regarding the adaptive significance of building multiple nests in a south temperate population of Grass Wrens. Building non-breeding nests was not a strategy of males to attract additional females, as most of these nests were built after pair formation and both sexes collaborated during building. Building non-breeding nests was not a post-pairing display as the presence of multiple nests did not increase female investment in the breeding attempt: clutch size and female provisioning to nestlings did not differ between experimental and control territories where no non-breeding nests were removed. Similarly, in non-manipulated territories, clutch size and female provisioning were not correlated with the number of non-breeding nests or with males’ nest-building effort. Contrary to this hypothesis, the number of non-breeding nests was associated with delayed clutch initiation and reduced hatching success. The presence of non-breeding nests did not reduce nest predation and brood parasitism, which did not differ between experimental and control territories. We did not detect differences in concealment between non-breeding and breeding nests, suggesting that non-breeding nests were not the result of abandonment before egg-laying to reduce subsequent nest predation. Dummy nests did not provide shelter; they were not used frequently for roosting over the breeding season and were not maintained during the non-breeding season. We suggest that building non-breeding nests may be an attempt by males to manipulate the decision of females to breed with a mate they might otherwise reject or to start reproduction earlier than optimal for the females.     

Sharing of caring: nestling provisioning behaviour of long-tailed tit, Aegithalos caudatus, parents and helpers

The optimal investment strategies of parents in biparental systems are well studied. This contrasts with a poor theoretical and empirical understanding of variation in individual investment in breeding systems with multiple carers. We used the cooperative breeding system of long-tailed tits, to investigate how parents and helpers adjust their rate of nestling provisioning in relation to measures of nestling demand and the number of helpers. Our aim was to examine whether parents and helpers follow the same provisioning rules. Overall provisioning rates were higher for parents than for helpers. However, both parents and helpers increased their provisioning rates as nestlings aged and provisioned at higher rates early in the day. Parents brought more food to larger broods when not helped, but at nests with helpers, neither parents nor helpers had significantly higher provisioning rates at larger broods. However the total provisioning rate was higher at larger broods at both nests with and without helpers. Parents reduced their work rate in response to the arrival of a helper, but neither parents nor first helpers reduced their work rates further with arrival of additional helpers. Variation in provisioning rates between parents and helpers may be the result of different cost-benefit relations, and a theoretical framework is needed within which to explore the consequences of such differences. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.      

Plural Breeding in the Splendid Fairy-wren,Malurus splendens (Aves: Maluridae), a Cooperative Breeder

Groups of the cooperatively breeding splendid fairy-wren Malurus splendens may include more than one female. Previously this species has been described as singular breeding (only one female breeds). This paper describes the occurrence of plural breeding (PB) groups in 10% of group years, in which two females had separate nests. In all cases, the secondary female (Y) was related to the primary breeding female (X) and was generally a 2-year old female which had helped in the group during the previous breeding season. Plural breeding was correlated with an increase in population density and in the number of female helpers; PB groups were larger than singular-breeding groups. In most cases, the X female was occupied with her own nest or offspring when the Y female began to nest, and there was no aggression between them. Which birds helped the Y female to feed at her nest depended on the time between the hatching of the two nests. If the interval was small, some group members helped at each nest; with longer intervals, the group members began to feed at the earlier nest, and the other female was left to raise her brood alone. Female helpers were very active in feeding at single nestings, and the cost to an X female of a Y female breeding was mainly a loss of this assistance. The success of individual X nests was not affected. Effects on productivity were slight, but fewer X females in PB groups raised second broods than did experienced singular breeding females. Y females were less productive than X females, but no less productive than singular breeding novice females without helpers. It is not known whether Y females copulated with primary or secondary males within their group, or with males from outside the group. Certainly, they did not form an observable pairing with any male in the group. Plural breeding occurred in a minority of group years in response to extrinsic conditions and the current demographic situation, and shows the extreme plasticity of the mating system in M. splendens.     

Territory quality drives intraspecific patterns of extrapair paternity

Despite the potential reproductive benefits of extrapair matings,extrapair paternity rates in many avian species often vary greatlyamong populations. Although ecological factors have been shownto influence intraspecific patterns of extrapair paternity insome species, for cooperatively breeding species living in familygroups, social/demographic factors may also play a role. Thisstudy examined how ecological factors related to territory quality(vegetation cover, insect abundance) and social/demographicfactors (group size, number of breeding pairs, genetic relatedness)influenced intraspecific patterns of extrapair paternity incooperatively breeding superb starlings, Lamprotornis superbus.Superb starlings inhabit spatiotemporally variable African savannaswhere high temporal variability drives reproductive decisions(adoption of breeding roles, offspring sex allocation) and whereterritories suitable for breeding are limited. Although extrapairpaternity rates were only 14% of offspring and 25% of nests,they varied greatly among groups, ranging from 4% to 32% ofoffspring and from 7% to 60% of nests. These among-group differencesin extrapair paternity were not related to social/demographicfactors but instead to territory quality; extrapair paternitywas higher on lower quality territories (lower vegetation coverand grasshopper abundance) than on higher quality territories(higher vegetation cover and grasshopper abundance). These resultssuggest that even in a heterogeneous landscape where suitablebreeding territories are limited, subtle differences in habitatquality can have profound effects on reproductive decisionsand patterns of extrapair paternity. Understanding the interactionbetween spatial (habitat heterogeneity) and temporal (temporalvariability) environmental variation will be important for determininghow environmental and social factors drive avian reproductiveand mating decisions.     

Neural correlates of behavioural olfactory sensitivity changes seasonally in European starlings

Background

Possibly due to the small size of the olfactory bulb (OB) as compared to rodents, it was generally believed that songbirds lack a well-developed sense of smell. This belief was recently revised by several studies showing that various bird species, including passerines, use olfaction in many respects of life. During courtship and nest building, male European starlings (Sturnus vulgaris) incorporate aromatic herbs that are rich in volatile compounds (e.g., milfoil, Achillea millefolium) into the nests and they use olfactory cues to identify these plants. Interestingly, European starlings show seasonal differences in their ability to respond to odour cues: odour sensitivity peaks during nest-building in the spring, but is almost non-existent during the non-breeding season.

Methodology/Principal Findings

This study used repeated in vivo Manganese-enhanced MRI to quantify for the first time possible seasonal changes in the anatomy and activity of the OB in starling brains. We demonstrated that the OB of the starling exhibits a functional seasonal plasticity of certain plant odour specificity and that the OB is only able to detect milfoil odour during the breeding season. Volumetric analysis showed that this seasonal change in activity is not linked to a change in OB volume. By subsequently experimentally elevating testosterone (T) in half of the males during the non-breeding season we showed that the OB volume was increased compared to controls.

Conclusions/Significance

By investigating the neural substrate of seasonal olfactory sensitivity changes we show that the starlings'' OB loses its ability during the non-breeding season to detect a natural odour of a plant preferred as green nest material by male starlings. We found that testosterone, applied during the non-breeding season, does not restore the discriminatory ability of the OB but has an influence on its size.     

Infestations of Ornithonyssus bursa,a haemotophagous mite,on starlings over the non-breeding season

Abstract

Ornithonyssus bursa (Berlese) (Dermanyssidae) is found in nests and neotboxes and on nestlings of the starling (Sturnus vulgaris L.), sometimes in large numbers, during the breeding season. During the non-breeding season the nestboxes and nest material are devoid of live mites. O. bursa overwinters ectoparasitically on starlings, and is present on approximately 25% of the population at the beginning of the breeding season. These nucleus populations build up rapidly in nest boxes during the breeding season.     

Group Structure,Nest Size and Reproductive Success in the Cooperatively Breeding Cichlid Julidochromis ornatus: A Correlation Study

The effect of group size on reproductive success has long been studied in cooperatively breeding species, as it might provide an adaptive explanation for group‐living in social species. Numerous studies have shown positive effects of subordinates on reproductive success (‘helper effect’), but these studies have also revealed the importance of controlling statistically, or experimentally, for the effect of other factors that might affect reproductive success. Here, we first examine the relationships between group size, body size of group members and nest size in the cooperatively breeding cichlid Julidochromis ornatus, in which unrelated helpers frequently participate in reproduction and their breeding nests inside rock crevices may be crucial for reproduction and survival of all group members. Then, we subsequently investigate the relationship between group size and reproductive success, while controlling for these factors. The results showed that group size was significantly related to body size of group members rather than nest size; and larger breeders had larger helpers. It was found that group size significantly increased group reproductive output. More importantly, reproductive success of male breeders did not depend on the presence of mature helpers, whereas female reproductive success increased when two males assisted her and tended to decrease when two females bred cooperatively. We conclude that breeding groups of J. ornatus have size hierarchical societies that relate to group size, and group composition of genetically unrelated and co‐breeding members affects their reproductive success.     

Behaviour of the haematophagous mite Ornithonyssus bursa in starling nest boxes in New Zealand

Abstract

Ornithonyssus bursa (Berlese) (Mesostigmata: Dermanyssidae) is a continuous ectoparasite of starlings, and infests most of their nests. Visits by non-resident starlings are considered to be the principal means by which mites spread to uninfested nests during the breeding season. Mites occur between the clenched toes of young nestlings, but as the nestlings' feathers grow and their preening ability develops, mites shift to between primaries and to folds of skin under the bill. After the nestlings fledge, mites migrate to the upper surfaces of the nest box, where some are able to regain contact with adult starlings which daily revisit their nests.     

Southern Lapwing Vanellus chilensis cooperative helpers at nests are older siblings

Cooperative breeding is rare in shorebirds, and when found it is thought to be due to polygamous mating (cooperative polygamy). Here we describe the social structure of cooperatively breeding groups in Southern Lapwing Vanellus chilensis and test the prediction that offspring sex ratio is skewed towards the sex that helps. The social groups consisted of a breeding pair with one or two young (mostly males, 68%) from the previous breeding season, and offspring sex ratio was not skewed. Cooperative breeding in the Southern Lapwing is not the consequence of cooperative polygamy, but rather groups were formed by a mated pair and some of their offspring from previous nests as helpers.     

Sexual aggression by intruders in hooded crow <Emphasis Type="Italic">Corvus cornix</Emphasis>

The hooded crow Corvus cornix is a west Palaearctic, solitary nesting, monogamous corvid. In the breeding season, populations are characterized by a social organization wherein breeding pairs are territorial and non-breeding individuals, called floaters, live in flocks. During a study of the breeding ecology of the hooded crow, conducted in a protected flooded area, we monitored nests with video cameras. We recorded two separate incidents when intruders attacked a female at the nest. We believe that she remained in the nest in order to prevent the strangers cannibalizing the nestlings by mantling over the brood. The spatio-temporal occurrence of these attacks suggests that the observed behaviour is intraspecific sexual aggression wherein non-breeding males mounted an immobilized female.