Silva S.D.,University of Pennsylvania |
Silva S.D.,Uda Walawe Elephant Research Project |
Ranjeewa A.D.G.,Uda Walawe Elephant Research Project |
Ranjeewa A.D.G.,Open Box |
Weerakoon D.,University of Colombo
Biological Conservation | Year: 2011
We provide estimates of population size and other demographic variables for individually-identified Asian elephants (Elephas maximus) in Uda Walawe National Park (UWNP), Sri Lanka based on systematic year-round observations. Two hundred and eighty-six adult females and 241 adult males were identified, of which four adults (2% of males) had tusks. Sightings-based demographic models showed seasonal immigration and emigration from the study area. The total population, including non-adults, was between 804 and 1160 individuals. Density ranged from 102 to 116 adult females per 100 km2 and remains at this level throughout the year. This large, un-fragmented population of Asian elephants should be of high conservation priority. We find that estimates of survivorship and migration rates should be based on long sampling intervals when possible, but estimates of density and population size can still be made when observations are constrained to shorter intervals, if spatial data are available. We offer suggestions to guide census design for other elephant populations or cryptic species. We urge that other locations be systematically surveyed as well using photographic identification. © 2011 Elsevier Ltd.
De Silva S.,University of Pennsylvania |
De Silva S.,Uda Walawe Elephant Research Project |
Ranjeewa A.D.G.,Uda Walawe Elephant Research Project |
Ranjeewa A.D.G.,Open University of Sri Lanka |
Kryazhimskiy S.,Harvard University
BMC Ecology | Year: 2011
Background: Patterns in the association of individuals can shed light on the underlying conditions and processes that shape societies. Here we characterize patterns of association in a population of wild Asian Elephants at Uda Walawe National Park in Sri Lanka. We observed 286 individually-identified adult female elephants over 20 months and examined their social dynamics at three levels of organization: pairs of individuals (dyads), small sets of direct companions (ego-networks), and the population level (complete networks).Results: Corroborating previous studies of this and other Asian elephant populations, we find that the sizes of elephant groups observed in the field on any particular day are typically small and that rates of association are low. In contrast to earlier studies, our longitudinal observations reveal that individuals form larger social units that can be remarkably stable across years while associations among such units change across seasons. Association rates tend to peak in dry seasons as opposed to wet seasons, with some cyclicity at the level of dyads. In addition, we find that individuals vary substantially in their fidelity to companions. At the ego-network level, we find that despite these fluctuations, individuals associate with a pool of long-term companions. At the population level, social networks do not exhibit any clear seasonal structure or hierarchical stratification. © 2011 de Silva et al; licensee BioMed Central Ltd.
News Article | October 11, 2016
Elephants are commonly thought to live in female-led, or matriarchal, societies that rely on the strong leadership and wisdom of elders. But a new study on Asian elephants led by researchers at Colorado State University found that Asian elephants, unlike African savannah elephants, do not exhibit clear dominance hierarchies or matriarchal leadership. Shermin de Silva, director of the Uda Walawe Elephant Research Project; CSU Associate Professor George Wittemyer; and Volker Schmid, biologist at the University of Regensburg, compared dominance interactions exhibited by adult female Asian elephants in Sri Lanka and a similarly aged group of female African savannah elephants in Kenya. The researchers found that Asian elephants showed less than one-third the amount of dominance behavior as their African counterparts. As a result, it was impossible to construct linear hierarchies among individuals, in contrast to the African females, for which dominance patterns were clear. "Female Asian elephants are a bit more like lionesses than like African savannah elephants," said de Silva, who conducted this research while a postdoctoral fellow at Colorado State University. The team also explored whether there might be more orderly hierarchies among elephants of different age groups or social groups in Sri Lanka. While the older elephants did tend to "win" confrontations more often in both populations, the Asian elephants showed a greater tendency for younger individuals to dominate older elephants. The animals also showed no real order by social group, which contrasts with African elephants. What might explain these differences? The classic view of elephants is based on decades of research on African savannah elephants, which found that females and calves form highly cohesive families with clear age-based dominance hierarchies. Such societies are favored under the ecological conditions savannah elephants typically find themselves in, namely where rainfall is unpredictable and resources are widely dispersed. These environments also contain large predators, and there is a great deal of competition among elephants for access to the best and safest areas. Asian elephants live in more productive and predictable environments where food and water are historically not difficult to come by. In this particular study, the elephants lived on an island that is free of large predators, such as tigers, and they had little to fear. Team members said that this frees up the elephants to make their own movement decisions, without the need to rely on the knowledge of others, or tolerate being dominated by them. The researchers refer to this phenomenon as an "ecological release." Asian elephants and African savannah elephants belong to two different species, separated by 6 million years of evolution. This is comparable to the split between humans and chimpanzees. Based on the findings, the researchers said that elephants may be prone to experiencing increased conflict when confined to smaller areas, where movements are more constrained and direct competition cannot be avoided. A James Smithson fellow at the Smithsonian Conservation Biology Institute, de Silva is founder of the conservation nonprofit Trunks & Leaves Inc. Wittemyer also serves as scientific director of Save the Elephants.
Da Silva S.,Uda Walawe Elephant Research Project |
Da Silva S.,Colorado State University |
Weerathunga U.S.,Uda Walawe Elephant Research Project |
Pushpakumara T.V.,Uda Walawe Elephant Research Project
BMC Research Notes | Year: 2014
Background: Dwarfism is a condition characterized by shorter stature, at times accompanied by differential skeletal growth proportions relative to the species-typical physical conformation. Causes vary and are well-documented in humans as well as certain mammalian species in captive or laboratory conditions, but rarely observed in the wild. Case presentation: We report on a single case of apparent dwarfism in a free-ranging adult male Asian elephant in Sri Lanka, comparing physical dimensions to those of other males in the population as well as in previous literature. The subject M459 was found to have a shoulder height of approximately 195 cm, is shorter than the average height of typical mature males, with a body length of 218 cm. This ratio of body length to height deviates from what is typically observed, which is approximately 1:1, but was similar to the attributes of a dwarf elephant in captivity documented in 1955. We report on behavior including the surprising observation that M459 appears to have a competitive advantage in intrasexual contests. We discuss how this phenotype compares to cases of dwarfism in other non-human animals. Conclusion: M459 exemplifies a rare occurrence of disproportionate dwarfism in a free-ranging wild mammal that has survived to reproductive maturity and appears otherwise healthy. © 2014 de Silva et al.; licensee BioMed Central.