Infanticide Avoidance Research Articles

Mother-offspring proximity maintenance as an infanticide avoidance strategy in bornean orangutans (Pongo pygmaeus wurmbii).

Sexually-selected infanticide by males is widespread across primates. Maternal protection is one of many infanticide avoidance strategies employed by female primates. Bornean orangutan (Pongo pygmaeus wurmbii) mothers with younger offspring are less social with males than mothers with older offspring. Additionally, the distance between a mother and offspring decreases in the presence of male conspecifics, but not female conspecifics. We hypothesized that mothers are responsible for the change in mother-offspring proximity when males are present. Using a year of behavioral data from orangutans in Gunung Palung National Park, we tested whether the Hinde Index, a ratio of the number of approaches and leaves between two individuals, was indicative of mother or offspring proximity maintenance across different social groupings. The semi-solitary social organization of orangutans allows us to observe different social groupings. We found that the mother-offspring Hinde Index was typically indicative of offspring maintenance of proximity. However, the presence of male conspecifics was associated with an increase in the Hinde Index which indicates that mothers are responsible for the decrease in mother-offspring distance when males are present. The decrease in mother-offspring distances and increase in Hinde Index when males are present indicates that mothers react to the presence of males in a protective manner. We suggest this may be an infanticide avoidance behavior by mother orangutans.

Stronger maternal social bonds and higher rank are associated with accelerated infant maturation in Kinda baboons

Social relationships are critical components of health and fitness for humans and other animals. For female-philopatric species, affiliative relationships among females (kin and nonkin alike) can influence components of fitness that include individual survival, interbirth interval and offspring survival. Affiliative relationships with males have attracted somewhat less attention, with most studies focusing on female–male relationships as adaptations for infanticide avoidance. Here, we use 8 years of behavioural data on Kinda baboons, Papio kindae , to assess whether maternal social relationships—both among females and between females and males—affect infant survival, interbirth interval and the pace of infant development. Kinda baboons are an ideal system for these analyses because males and females form strong relationships outside of the periovulatory period and in the absence of obvious infanticide threat. We calculated social metrics that reflected dominance status, total social integration and social bond strength and paired these metrics with data on offspring survival, interbirth interval (IBI) duration and infant behavioural maturation. Neither dominance rank nor sociality had a significant effect on interbirth interval or survival, but higher rank and the stronger affiliative relationships between a female and her top female and top male social partners predicted more rapid infant behavioural maturation. These results suggest that maternal dominance and sociality may confer advantages related to infant development and independence that ultimately may permit females to more quickly invest in subsequent offspring and point to advantages of relationships with males outside of lowering infanticide threat. • Kinda baboon female–male bonds persist outside of fertility or infanticide threat. • Social bonds did not affect interbirth interval or infant survival and growth. • Dominance and affiliative bonds predicted more rapid infant development. • Top-partner bonds were the strongest predictors of infant development. • Strong maternal bonds with females and males enhanced infant development.

The context of sexual coercion in orang-utans: when do male and female mating interests collide?

Sexual coercion is widespread in the animal kingdom. Its direct forms, including harassment and forced copulation, have largely been investigated as an expression of (alternative) male reproductive strategies, rather than the result of a sexual conflict between the sexes. Likewise, the frequent occurrence of forced copulations in orang-utans (Pongo spp.) has been attributed to male strategies and more recently also to concealed female fecundity. So far, however, the immediate contextual variables leading to forced copulations have rarely been examined. We compared two orang-utan populations, Suaq (Pongo abelii, Sumatra) and Tuanan (Pongo pygmaeus, Borneo), both characterized by an individual-based fission–fusion lifestyle, whereas their socioecology differs. We assessed how the occurrence of female-resisted and voluntary copulations was affected by female reproductive state, male morph (unflanged or flanged), measures of male–male competition, male–female relationship and ecological factors. Besides female reproductive state and male morph, predictors of female resistance were related to male–male competition. First, female resistance was more likely towards subordinate males who were displaced from proximity to the female by another male during that association. Second, the presence of additional flanged males increased the probability of female resistance. Third, the latency to both the arrival of another male and to the end of the association after sexual interactions was shorter if there was female resistance. We conclude that sexual coercion in orang-utans is highly dependent on the vicinity of more dominant males and can only be understood in the light of sexual conflict: While males force copulations when at risk of losing access to a female and thus follow a ‘now-or-never’ strategy, female resistance follows a ‘not-you-now’ pattern, which is ultimately consistent with an infanticide avoidance strategy.

Female-committed infanticide followed by juvenile-enacted cannibalism in wild white-faced capuchins

On 5 February 2021, we observed the first instance of female-committed infanticide followed by cannibalism in a long-studied (> 35 years) population of wild white-faced capuchins (Cebus imitator) in the Santa Rosa Sector of the Área de Conservación Guanacaste, Costa Rica. The events leading up to and including the infanticide and cannibalism were observed and documented ad libitum, with segments digitally recorded, and a post-mortem necropsy performed. Here we detail our observations and evaluate the events within the framework of leading adaptive explanations. The infanticide may have been proximately motivated by resource competition or group instability. The circumstances of the observed infanticide provided support for the resource competition, adoption avoidance, and social status hypotheses of infanticide, but not for the exploitation hypothesis, as neither the perpetrator nor her kin consumed the deceased infant. The subsequent cannibalism was performed by juveniles who observed the infanticide and may have been stimulated by social facilitation and their prior experience of meat consumption as omnivores. To our knowledge, cannibalism has been documented only once before in C. imitator, in an adjacent study group, with the two cases sharing key similarities in the context of occurrence and manner of consumption. These observations add to our growing knowledge of the evolutionary significance of infanticide and its importance as a reproductive strategy in nonhuman primates.

Direct Stacked Investment Is a Flexible Reproductive Strategy for Female Colobus vellerosus

Most primates produce one offspring at a time but can overlap investment in consecutive offspring (stacked investment) depending on ecological and/or social conditions. “Direct stacked investment” occurs when a female conceives and gestates a new offspring while a previous infant is still suckling. We investigate direct stacked investment in Colobus vellerosus by determining if there is a period of overlap between nipple contact with a female’s first infant and gestation of her subsequent infant. We then investigate the effect of male group-membership and stability on stacked investment to test the hypothesis that stacking investment is a female strategy to avoid infanticide. We collected scan data to record when an infant was in nipple contact from 16 females in four groups of C. vellerosus, from May 2012 to May 2013 at Boabeng-Fiema Monkey Sanctuary in Ghana. We studied three group types, stable multimale, multifemale; unstable multimale, multifemale; and stable unimale, multifemale. Eight of our study females directly stacked investment. The frequency of direct stacked investment varied significantly among the group types. Stacked investment was due to earlier conception rather than delayed weaning, with females in stable multimale groups conceiving a subsequent infant earlier than those in unstable multimale groups. The timing of conception did not differ between stable unimale groups and either unstable or stable multimale groups. There was no difference in time to last nipple contact among group types. These results do not support the predictions of the infanticide avoidance hypothesis, but a larger sample size would help to test the hypothesis more comprehensively. Delayed conception by females in unstable groups may be infanticide avoidance, however, if it allows time for females to spread paternity certainty among males. Alternatively, females in unstable groups may be under stress or experience reduced feeding time due to frequent male–male agonistic interactions, both of which can suppress female ovulation. This study contributes to a growing body of research that explores flexibility in infant investment strategies, particularly in relation to external factors such as male group membership and stability.

Multilevel societies facilitate infanticide avoidance through increased extrapair matings

In mammals characterized by a mating system in which a single male monopolizes reproduction, infanticide is reported to occur following a male take-over, often resulting in females returning to oestrus more rapidly than if their infant has survived. However, over the course of a 17-year study of golden snub-nosed monkeys, Rhinopithecus roxellana, a polygynous colobine species, we found no behavioural or suspected evidence of infanticide. Based on social network and genetic analyses, we found that more than half of the infants were sired as a result of extrapair matings (EPMs). Female golden snub-nosed monkeys initiated EPMs with bachelor or neighbouring resident males. These were considered ‘sneaky’ copulations because they did not occur in the presence of the leader male of the female's one-male unit (OMU). We suggest that through a process of paternity confusion, females decreased the likelihood of infanticide after a male take-over. In contrast, in a group of the same species in which the number of bachelor males was artificially reduced, EPMs were infrequent and four cases of infanticide were observed, three of them following a male take-over. Golden snub-nosed monkeys reside in a large multilevel society that develops by the fusion of several independent OMUs to form a breeding band, which is characterized by increased social cohesion and intrasexual tolerance among leader males. Females play an active role in mate choice, and engage in a diverse set of mating tactics, including counterstrategies such as EPMs to avoid infanticide. These results offer new insights into the diversity of behavioural strategies facilitated by complex social structures in nonhuman primates, as well as other social mammals.

Are Male Orangutans a Threat to Infants? Evidence of Mother–Offspring Counterstrategies to Infanticide in Bornean Orangutans (Pongo pygmaeus wurmbii)

Sexually selected infanticide by males is widespread in primates. Female primates employ a variety of strategies to reduce infanticide risk. While infanticide has never been directly observed in wild orangutans (Pongo spp.), their slow life history makes infants vulnerable to infanticide. The mating strategies of female orangutans include polyandrous and postconceptive mating that may serve to increase paternity confusion, an infanticide avoidance strategy. Here, we investigate whether female orangutans alter their social interactions with males as another infanticide avoidance strategy. We hypothesize that females with younger offspring avoid males and that the distance between mother and offspring decreases in the presence of males. We use long-term behavioral data collected between 1994 and 2016 from Bornean orangutans (Pongo pygmaeus wurmbii) in Gunung Palung National Park, Indonesia, to test whether the sexual selection hypothesis for infanticide helps explain aspects of orangutan social behavior. We found that mothers with offspring 6 yr. old and females without offspring. In addition, the distance between a mother–offspring dyad showed a statistically significant decrease in the presence of males, but not females. Our results are consistent with the hypothesis that female orangutans employ strategies to reduce infanticide risk in their social interactions. Because orangutans have a high fission–fusion dynamic, they have flexibility in manipulating social interactions as a counterinfanticide strategy. Our results suggest that infanticide by males is a selective pressure shaping female orangutan social behavior.

Possible Male Infanticide in Wild Orangutans and a Re-evaluation of Infanticide Risk

Infanticide as a male reproductive tactic is widespread across mammals, and is particularly prevalent in catarrhine primates. While it has never been observed in wild orangutans, infanticide by non-sire males has been predicted to occur due to their extremely long inter-birth intervals, semi-solitary social structure, and the presence of female counter-tactics to infanticide. Here, we report on the disappearance of a healthy four-month-old infant, along with a serious foot injury suffered by the primiparous mother. No other cases of infant mortality have been observed at this site in 30 years of study. Using photographic measurements of the injury, and information on the behavior and bite size of potential predators, we evaluate the possible causes of this injury. The context, including the behavior of the female and the presence of a new male at the time of the injury, lead us to conclude that the most likely cause of the infant loss and maternal injury was male infanticide. We suggest that in orangutans, and other species where nulliparous females are not preferred mates, these females may be less successful at using paternity confusion as an infanticide avoidance tactic, thus increasing the likelihood of infanticide of their first-born infants.

Reproductive class influences risk tolerance during denning and spring for American black bears (Ursus americanus)

AbstractDen sites are important for many species’ ecology, and individuals should choose den sites that minimize risk and maximize energy gain. We examined den site selection and spring space use for black bears (Ursus americanus) at the individual level, and analyzed support for the anthropogenic risk avoidance and infanticide avoidance hypotheses. We obtained telemetry data for 94 individual bears (71 F and 23 M) and collected 162 den locations from Michigan (2009–2011 and 2013–2015), Missouri (2010–2016), and Mississippi (2008–2017), USA. Of 71 females, 37 were monitored during multiple reproductive states. We used generalized linear mixed models to evaluate the influence of reproductive state (female with cubs, female with yearlings, female alone, or male) on den distance to the nearest road, two road indexes (den emergence and spring), spring home range size, mean spring road distance, and a NDVI selection index. All black bears, except females with cubs, chose den locations farther from roads than available to them, supporting the anthropogenic risk avoidance hypothesis. Additionally, females with cubs displayed the smallest spring home ranges among females, as well as denned closer to roads and used areas closer to roads during spring than females with yearlings, supporting the infanticide avoidance hypothesis. The differential responses by the same females when having cubs or yearlings point to strategies to maximize reproductive success. By investigating behavior considering individual availability, we revealed patterns that might not be detected by population‐level assessments.

Why do female mice mate with multiple males?

Females often show multi-male mating (MMM), but the adaptive functions are unclear. We tested whether female house mice (Mus musculus musculus) show MMM when they can choose their mates without male coercion. We released 32 females into separate enclosures where they could choose to mate with two neighboring males that were restricted to their own territories. We also tested whether females increase MMM when the available males appeared unable to exclude intruders from their territories. To manipulate territorial intrusion, we introduced scent-marked tiles from the neighboring males into males' territories, or we rearranged tiles within males' own territories as a control. Each female was tested in treatment and control conditions and we conducted paternity analyses on the 57 litters produced. We found that 46 % of litters were multiply sired, indicating that multiple paternity is common when females can choose their mates. Intrusion did not increase multiple paternity, though multiple paternity was significantly greater in the first trial when the males were virgins compared to the second trial. Since virgin male mice are highly infanticidal, this finding is consistent with the infanticide avoidance hypothesis. We also found that multiple paternity was higher when competing males showed small differences in their amount of scent marking, suggesting that females reduce MMM when they can detect differences in males' quality. Finally, multiple paternity was associated with increased litter size but only in the intrusion treatment, which suggests that the effect of multiple paternity on offspring number is dependent on male–male interactions.

Proximity association in polygynous western black crested gibbons ( Nomascus concolor jingdongensis ): network structure and seasonality

We investigated the structure and seasonality of the proximity network in a group of polygynous western black crested gibbons (Nomascus concolor) using social network analysis. The spatial proximity changed seasonally and was affected by temperature and rainfall. Preferred proximity association was not distributed randomly among individuals. Kinship was one explanation for the social structure, as offspring preferred to maintain close proximity with their mothers. The proximity of infants to mothers decreased with age, and independent offspring had lower proximity to mothers than dependent ones. We found that the adult male had different proximity relationships with two different adult females. The frequency of proximity between the male and the infant-carrying female was significantly higher than that between the male and the female who had immigrated carrying one offspring of uncertain paternity into the group. Infanticide avoidance and/or predation protection for dependent infants might explain the proximity relationship differences. Temperature influenced group proximity association, with individual proximity increasing in the cold months and decreasing in the hot months. Group proximity decreased in months with higher anthropogenic disturbance.

Roaring Behavior of Two Syntopic Howler Species (Alouatta caraya and A. guariba clamitans): Evidence Supports the Mate Defense Hypothesis

Long-distance calls are loud vocalizations involved in within and between group communication in animals. These calls may maintain cohesion with group members or communicate the ownership of valuable resources such as territory, food, or mates to individuals from other groups. In howlers (Alouatta spp.), three nonmutually exclusive hypotheses suggest that the ultimate function of roaring (howling) behavior is to protect resources from neighboring groups. The space/food defense hypothesis maintains that roars are used to gain exclusive access to food; the mate defense hypothesis holds that roars ensure exclusive access to mates; and the infanticide avoidance hypothesis states that the roaring behavior serves to avoid male takeovers and infanticide. To test these three hypotheses, we conducted a study on black-and-gold howlers (Alouatta caraya) and brown howlers (A. guariba clamitans) living in syntopy at El Pinalito provincial park in northeast Argentina. We recorded 12 mo of data on the roaring behavior of two groups of each species, along with data on food availability and diet. Although all four groups overlapped extensively in their use of food resources during the study period, roars occurred much more frequently during interactions between groups of the same species than between groups of different species. Roaring frequency was not higher during the lean season, when high-quality food was less abundant. Howlers did not roar more frequently at home range boundaries, nor were roaring bouts spatially associated with valuable feeding resources. Males participated in all of the roaring bouts, whereas females participated in only 29% of them. Adults did not roar more frequently when there were unweaned infants in the group, as expected if roaring behavior decreases infanticide risk. These results provide no support for the food defense or infanticide avoidance hypotheses, but support predictions derived from the mate defense hypothesis.

Observed infanticides following a male immigration event in black howler monkeys, Alouatta pigra, at Palenque National Park, Mexico

This study describes two cases of directly observed and one case of nearly observed infanticide after an adult male immigrated into a multimale-multifemale group of black howler monkeys (Alouatta pigra) at Palenque National Park, Mexico. The immigrant male entered the group alone, injured the central adult male, presumably evicted the noncentral adult male, and killed all three young infants present over the course of three consecutive days in February 2010. Three weeks after the infanticide events, the three adult females who lost their infants were observed to sexually solicit and copulate with both the infanticidal male and the injured central male. Multimale mating is an effective reproductive strategy that females employ to confuse paternity and reduce the risk of infanticide, but the extent to which promiscuous mating after infanticide events is part of a counterstrategy in this species is still unknown. More cases of infanticide will need to be observed to assess the degree to which infanticide avoidance shapes the social system of the black howler monkey.

The determinants of fertility among Australian Aborigines.

This paper concerns the determinants of fertility of precontact Australian Aborigine women. Emphasis is placed on social organization as well as the physical environment and considerations of adaptation. The key to understanding the fertility of Australian Aborigines is the structural tension evident in male-female relations. Ethnographic data on hunter-gatherers fertility indicate a low fertility rate, e.g. 4.7-5.2 live births/woman for the Kung. Traditional Aboriginal physiological fertility was also low if infant mortality is separated from infertility. Past studies of population and transition theory in pre-contact situations have attributed increase in population to reduction in mortality. This paper suggests that there must have been an increase in the birth rate. Factors affecting ovulation, conception, and parturition are examined for traditional Aboriginal populations. Ovulation is affected by nutrition, lactation, and introcision. Lack of body fat in women causes anovulation due to insufficent energy reserves. Increased fertility appears to be a greatly reduced energy expenditure and an increased carbohydrate intake leading to a build up of body weight. Pre-contact Aboriginal fertility was low because of a low caloric intake and a high energy expenditure. Prolonged lactation does not seem to cause birth spacing. The actual length of time after parturition appears to be an independent cause of reduced prolactin, and of reestablishment of ovulation. Stress and anxiety are factors which could reduce fertility by causing anovulation in women and/or reduced sperm counts in men. Contraception is affected by coital frequency and male fertility. Aboriginal coital frequency may have been affected by the lack of privacy and competition of a co-wife. Gestation is affected by spontaneous abortion, sterility, and foetal wastage. Harsh conditions of traditional Aborigines may have affected their ability to conceive. Voluntary controls on fertility for Aborigines include rituals, avoidance of coitus, taking medicines, abortion, and infanticide. Low fertility of precontact aborigines is accounted for by diet and energy expenditure, with limited coital frequency and foetal wastage as probable contributing factors. Fallopian tube blockage could account for the high rate of infertility of women. Social organization, values, and beliefs are important to take into account.

Female reproductive strategies in orangutans, evidence for female choice and counterstrategies to infanticide in a species with frequent sexual coercion.

Intersexual conflicts over mating can engender antagonistic coevolution of strategies, such as coercion by males and selective resistance by females. Orangutans are exceptional among mammals for their high levels of forced copulation. This has typically been viewed as an alternative mating tactic used by the competitively disadvantaged unflanged male morph, with little understanding of how female strategies may have shaped and responded to this behaviour. Here, we show that male morph is not by itself a good predictor of mating dynamics in wild Bornean orangutans but that female conception risk mediated the occurrence and quality of male-female interactions. Near ovulation, females mated cooperatively only with prime flanged males who they encountered at higher rates. When conception risk was low, willingness to associate and mate with non-prime males increased. Our results support the hypothesis that, together with concealed ovulation, facultative association is a mechanism of female choice in a species in which females can rarely avoid coercive mating attempts. Female resistance, which reduced copulation time, may provide an additional mechanism for mate selection. However, coercive factors were also important as prime males were frequently aggressive to females and females used mating strategies consistent with infanticide avoidance.

Leave or conceive: natal dispersal and philopatry of female mountain gorillas in the Virunga volcano region

Natal dispersal is often attributed to inbreeding avoidance, competition for resources or competition for mates, but the patterns and frequency of dispersal vary considerably among and even within species. We examined the possible reasons for dispersal and philopatry of natal nulliparous female mountain gorillas, Gorilla gorilla beringei , in the Virunga volcano region, including comparisons with non-natal and/or parous females. Competition among females is generally weak and ineffective in this population, and inbreeding avoidance has been considered the ultimate cause of natal dispersal. Yet fewer than half of nulliparous females left their natal group when the dominant male was old enough to be their father, so they did not rely entirely upon dispersal to avoid such risk of inbreeding. Almost all natal nulliparous females were with at least one sexually active male who was not old enough to be their father, so the presence or absence of such mating alternatives also did not determine whether they left. Natal nulliparous females were more likely to leave groups with only one adult male, where infanticide losses have been higher than in multimale groups. Thus natal dispersal seemed to be influenced by infanticide avoidance, which has been considered the ultimate cause of secondary dispersal. Natal nulliparous females have more time to encounter suitable destinations than other females, which may be a proximate reason why they were more likely to transfer despite having the same ultimate cause of dispersal.

Female dispersal in a female-philopatric species, Cebus capucinus

[White-faced capuchins ( Cebus capucinus ) reside in multimale–multifemale groups characterized by female philopatry and frequent male dispersal. However, over the years we have observed five females immigrate into our study groups and 23 disappear/emigrate. We examined long-term demographic and behavioural data on three groups of C. capucinus residing in Santa Rosa, Costa Rica, between 1986 and 2007. During this time, 56 females resided in our study groups and as of June 2007, 23 were still present, ten were confirmed/presumed dead and 23 were missing. Here we review the circumstances surrounding the five immigrations and 23 missing females and evaluate three main hypotheses to explain female dispersal in a female philopatric species: inbreeding avoidance, reduction of intragroup feeding competition and infanticide avoidance. The two main predictions of the inbreeding avoidance hypothesis were not supported by our study; male tenure did not exceed female age at first birth and the majority of dispersers were parous females. The reduction in intragroup feeding competition hypothesis received moderate support; dispersing/disappearing females tend to leave during the dry season and they have fewer matrilineal kin than females remaining in their natal group. Our data were most consistent with the infanticide avoidance hypothesis in that females are more likely to disperse/disappear during years with male replacements, a time when infant deaths are also more common. These data provide further evidence of the large impact that the movement and actions of adult male white-faced capuchins have on the lives of females in this species., White-faced capuchins ( Cebus capucinus ) reside in multimale–multifemale groups characterized by female philopatry and frequent male dispersal. However, over the years we have observed five females immigrate into our study groups and 23 disappear/emigrate. We examined long-term demographic and behavioural data on three groups of C. capucinus residing in Santa Rosa, Costa Rica, between 1986 and 2007. During this time, 56 females resided in our study groups and as of June 2007, 23 were still present, ten were confirmed/presumed dead and 23 were missing. Here we review the circumstances surrounding the five immigrations and 23 missing females and evaluate three main hypotheses to explain female dispersal in a female philopatric species: inbreeding avoidance, reduction of intragroup feeding competition and infanticide avoidance. The two main predictions of the inbreeding avoidance hypothesis were not supported by our study; male tenure did not exceed female age at first birth and the majority of dispersers were parous females. The reduction in intragroup feeding competition hypothesis received moderate support; dispersing/disappearing females tend to leave during the dry season and they have fewer matrilineal kin than females remaining in their natal group. Our data were most consistent with the infanticide avoidance hypothesis in that females are more likely to disperse/disappear during years with male replacements, a time when infant deaths are also more common. These data provide further evidence of the large impact that the movement and actions of adult male white-faced capuchins have on the lives of females in this species.]

Female dispersal patterns in six groups of ursine colobus (Colobus vellerosus): infanticide avoidance is important

Summary Under the dispersal/foraging efficiency model, colobines are predicted to be ‘indifferent mothers’, neither facilitating philopatry for their daughters nor evicting them from the natal home range because food competition is thought to be slight. We observed six groups of Colobus vellerosus at the Boabeng-Fiema Monkey Sanctuary in Ghana (2000‐2007) and recorded changes in female composition caused by observed (N = 11) and inferred (N = 12) emigrations and immigrations (N = 3). We also observed 14 immigration attempts. Most emigrating females were subadult and nulliparous. Parallel emigration was frequent. Resident females behaved aggressively to immigrating females and immigration attempts were rarely successful. Voluntary female emigration (N = 10) occurred mostly when male group membership was unstable or in association with the immigration of all-male bands. Involuntary emigrations (N = 13) associated with increased female‐female aggression occurred in the two largest groups, where parous females targeted nulliparous maturing females. Larger groups tended to lose females and female immigration was successful only in the study group with the lowest number of females. Females appear to emigrate to reduce infanticide threat although feeding competition is reduced in smaller groups as well. C. vellerosus at BFMS are better described as ‘incomplete suppressors’.

Female multiple mating and paternity in free-ranging North American red squirrels

Multimale mating (MMM) is common in female mammals, but our understanding of its evolutionary significance in this taxon lags behind that in others (e.g. invertebrates and birds). To date, the majority of research on mammalian MMM has been conducted under laboratory conditions, and the extent to which these findings have relevance for natural populations is little known. We quantified MMM in a free-ranging population of North American red squirrels, Tamiasciurus hudsonicus , and investigated its hypothesized influences and consequences. We observed 85 mating chases, representing 62 individual females, over three mating seasons and calculated standardized indexes of MMM and number of copulations. Extrinsic elements of mating chases (i.e. an index of the number of attending males and date) explained variation in MMM, while traits of the females (age and pre-oestrous body mass) did not correlate with MMM. Hypotheses of cryptic direct benefit (fertility assurance and infanticide avoidance) were not supported because MMM did not influence pregnancy rate, litter size or nest fate. There was also no correlation between MMM and offspring quality, multiple paternity or litter allelic diversity, and therefore, no support for hypotheses of genetic benefit. In addition to not accruing observable benefits to MMM, females did not incur a detectable cost, thus rendering MMM selectively neutral. Rather, in line with traditional explanations, female mating behaviour in red squirrels appears to be a passive response to selection on multifemale mating in males.

Why are Utah Prairie Dogs Vigilant?

Detection of predators, social monitoring, and avoidance of infanticide have been invoked to explain patterns of vigilance. To test these hypotheses, I examined the vigilance of 120 Utah prairie dogs (Cynomys parvidens )u sing ‘‘one–zero’’ sampling on individuals of known sex, reproductive state, and genealogy. Male and female prairie dogs increased vigilance during periods of heightened predation risk (i.e., with few surrounding conspecifics) unless the risk resulted from spatial positioning in the colony. Reproductive males and females were more vigilant than their nonreproductive counterparts during breeding, and estrous females increased vigilance in the presence of prospective mates. In contrast to predictions of the infanticide-avoidance hypothesis, lactating females were less vigilant than females without litters when neonates were in a nursery burrow and vulnerable to infanticide by males. Males were more vigilant than females, but not when the offspring of their sexual partners were vulnerable to infanticide or opportunities to kill offspring increased. I conclude that vigilance in Utah prairie dogs varies mostly in relation to the risk of predation. Mate competition also increases vigilance in males and females. However, prevention or facilitation of infanticide does not appear to influence vigilance in males or females.