Bates L.A.,University of St. Andrews |
Handford R.,University of St. Andrews |
Lee P.C.,University of Stirling |
Njiraini N.,Amboseli Trust for Elephants |
And 5 more authors.
PLoS ONE | Year: 2010
Female African elephants signal oestrus via chemicals in their urine, but they also exhibit characteristic changes to their posture, gait and behaviour when sexually receptive. Free-ranging females visually signal receptivity by holding their heads and tails high, walking with an exaggerated gait, and displaying increased tactile behaviour towards males. Parous females occasionally exhibit these visual signals at times when they are thought not to be cycling and without attracting interest from musth males. Using demographic and behavioural records spanning a continuous 28-year period, we investigated the occurrence of this "simulated" oestrus behaviour. We show that parous females in the Amboseli elephant population do simulate receptive oestrus behaviours, and this false oestrus occurs disproportionately in the presence of naïve female kin who are observed coming into oestrus for the first time. We compare several alternative hypotheses for the occurrence of this simulation: 1) false oestrus has no functional purpose (e.g., it merely results from abnormal hormonal changes); 2) false oestrus increases the reproductive success of the simulating female, by inducing sexual receptivity; and 3) false oestrus increases the inclusive fitness of the simulating female, either by increasing the access of related females to suitable males, or by encouraging appropriate oestrus behaviours from female relatives who are not responding correctly to males. Although the observed data do not fully conform to the predictions of any of these hypotheses, we rule out the first two, and tentatively suggest that parous females most likely exhibit false oestrus behaviours in order to demonstrate to naïve relatives at whom to direct their behaviour. © 2010 Bates et al.
Lee P.C.,University of Stirling |
Moss C.J.,Amboseli Trust for Elephants
Journal of Comparative Psychology | Year: 2012
Animal personalities have been demonstrated for almost 200 species, with stable dimensions of responses (aggressive to fearful; shy to bold) across contexts and with a heritable basis to these traits. As a long-lived and highly social species, elephants (Loxodonta africana) were expected to demonstrate complex dimensions to individual characteristics or personalities, which would be obvious to human observers and validated by behavioral observations. We used principal-components analysis of ratings on 26 behavioral adjectives applied to one social unit, coded as the EB family, which has been observed for 38 years. Eleven adult females were rated by four observers and found to have individually variable traits on four dimensions described by principal-components analysis. The first component was associated with effective and confident family leadership. Component 2 was age-related, and defined by playfulness, exploration and high levels of activity, suggesting both an experience and an age-related element to its structure. Component 3 represented gentleness and at its other extreme, aggression, and Component 4 was related to constancy (predictability and popularity), with both of these latter components reflecting social integration. Leadership among elephant females represents the successful negotiation among individual interests, and our components were related to a capacity to affect the behavior of others in the absence of aggressive dominance. The family matriarch, Echo, was high on elements associated with leadership. The importance of the matriarch in this family's success suggests that elements of personality may underlie interfamilial variation in long-term survival and reproduction. © 2012 American Psychological Association.
Chiyo P.I.,Duke University |
Chiyo P.I.,University of Notre Dame |
Moss C.J.,Amboseli Trust for Elephants |
Alberts S.C.,Duke University
PLoS ONE | Year: 2012
Factors that influence learning and the spread of behavior in wild animal populations are important for understanding species responses to changing environments and for species conservation. In populations of wildlife species that come into conflict with humans by raiding cultivated crops, simple models of exposure of individual animals to crops do not entirely explain the prevalence of crop raiding behavior. We investigated the influence of life history milestones using age and association patterns on the probability of being a crop raider among wild free ranging male African elephants; we focused on males because female elephants are not known to raid crops in our study population. We examined several features of an elephant association network; network density, community structure and association based on age similarity since they are known to influence the spread of behaviors in a population. We found that older males were more likely to be raiders than younger males, that males were more likely to be raiders when their closest associates were also raiders, and that males were more likely to be raiders when their second closest associates were raiders older than them. The male association network had sparse associations, a tendency for individuals similar in age and raiding status to associate, and a strong community structure. However, raiders were randomly distributed between communities. These features of the elephant association network may limit the spread of raiding behavior and likely determine the prevalence of raiding behavior in elephant populations. Our results suggest that social learning has a major influence on the acquisition of raiding behavior in younger males whereas life history factors are important drivers of raiding behavior in older males. Further, both life-history and network patterns may influence the acquisition and spread of complex behaviors in animal populations and provide insight on managing human-wildlife conflict. © 2012 Chiyo et al.
Lee P.C.,Amboseli Trust for Elephants |
Lee P.C.,University of Stirling |
Sayialel S.,Amboseli Trust for Elephants |
Lindsay W.K.,Amboseli Trust for Elephants |
And 2 more authors.
African Journal of Ecology | Year: 2012
We assess tooth-based age criteria for African elephants developed by Laws in relation to known-aged individuals in the Amboseli elephant population. Laws's technique remains a robust and useful mechanism for age determination, although we suggest revisions to the oldest age categories. Blind age assignment to jaws of unknown sex using the Laws criteria resulted in misclassification of M4 and M5; measures overlapped too much to differentiate these teeth by sex. Sexes could be reliably distinguished after age 30 or XIX in tooth category by two measures: mandible thickness and width of the ascending ramus, but individuals of the same known age differed in tooth wear and progression rates. Such variation needs to be incorporated in the error assigned to tooth age categories. Ages at death of found jaws (n=266) were similar to results of survival analysis from all demographic data (n=2455), excluding calves whose jaws decompose because of weathering and scavengers. Jaw-based models of age at death need correction for the inability to detect this early mortality, which artificially extends mean longevity by up to 6 years. © 2011 Blackwell Publishing Ltd.
Three generations of Amboseli elephants. Credit: Amboseli Trust for Elephants Only a few mammals and some birds are as long-lived as humans, and many of these species share interesting characteristics in how they age. A new paper in Springer's journal Behavioral Ecology and Sociobiology explores lifetime reproductive patterns in African elephants. Led by Phyllis Lee of the University of Stirling in the UK, the study analysed data from 834 female elephants in Amboseli National Park, Kenya. This population has been continuously monitored since 1972, and data collected on more than 3000 elephants since the study began. This paper analyses 42 years of data on females who survived to be at least nine years old. For long-lived species such as humans, chimpanzees, whales and some birds, longer survival is associated with higher reproductive rates and a loss in fertility only at an extremely old age. Prolonged post-reproductive lifespans may mean potential advantages for both the surviving individuals and their offspring; post-reproductive longevity thus remains a question of major theoretical interest. Elephant life histories are slow; a 22 month gestation period is followed by 12 months lactational anestrus, and calves suckle until their next sibling is born. Most females in this study gave birth by the age of 14, and as for other species, early starters have higher rates of reproduction. Most Amboseli females survived into their late thirties, while ten per cent lived into their sixties. According to Lee, elephants exhibit the classical mammalian pattern of a decline in reproductive rate after age 49, followed by up to sixteen years of post-reproductive survival. This classic life history phenomenon - the selective disappearance of less productive individuals - has not been demonstrated for such a long-lived animal before. Calf survival goes hand-in-hand with maternal experience and environmental conditions in the calf's first year of life, but is not directly related to the mother's age. First-born calves, those born during a drought and male offspring are more likely to die earlier than others. Even the oldest mothers (aged over 50) raised offspring successfully, although, like the mothers of sons, older mothers have slightly longer intervals between births. "The new and exciting part of our study is the strong effect females have on the reproduction of daughters and granddaughters in their family" says Lee. "Daughters of long-lived mothers lived longer themselves and had higher reproductive rates". In some large families, three generations of mother-daughter pairs reproduced simultaneously. Only ten of the 281 mothers monitored ceased reproduction towards the end of their lives. So while elephant calves clearly get a major survival and reproductive benefit from having a living grandmother, the females do not exhibit classical forms of menopause - or cessation of reproduction long before death - seen in whales and humans, despite having an average of a 16-year period between when a long-lived female's reproductive rate declines and her own death. Lee et al. argue that elephant reproduction is a function of a long-lived mother within a successful family context. The social dimension of grandmothering, such as environmental or social knowledge, appears to be a more important benefit in these female-led families than does a female trading off her own reproduction against that of her daughters, as is typically seen in humans. Explore further: Older killer whales make the best mothers More information: Phyllis C. Lee et al. The reproductive advantages of a long life: longevity and senescence in wild female African elephants, Behavioral Ecology and Sociobiology (2016). DOI: 10.1007/s00265-015-2051-5