Abstract
Juvenile mortality is a key factor influencing population growth rate in density-independent, predation-free, well-managed captive populations. Currently at least a quarter of all Asian elephants live in captivity, but both the wild and captive populations are unsustainable with the present fertility and calf mortality rates. Despite the need for detailed data on calf mortality to manage effectively populations and to minimize the need for capture from the wild, very little is known of the causes and correlates of calf mortality in Asian elephants. Here we use the world's largest multigenerational demographic dataset on a semi-captive population of Asian elephants compiled from timber camps in Myanmar to investigate the survival of calves (n = 1020) to age five born to captive-born mothers (n = 391) between 1960 and 1999. Mortality risk varied significantly across different ages and was higher for males at any age. Maternal reproductive history was associated with large differences in both stillbirth and liveborn mortality risk: first-time mothers had a higher risk of calf loss as did mothers producing another calf soon (<3.7 years) after a previous birth, and when giving birth at older age. Stillbirth (4%) and pre-weaning mortality (25.6%) were considerably lower than those reported for zoo elephants and used in published population viability analyses. A large proportion of deaths were caused by accidents and lack of maternal milk/calf weakness which both might be partly preventable by supplementary feeding of mothers and calves and work reduction of high-risk mothers. Our results on Myanmar timber elephants with an extensive keeping system provide an important comparison to compromised survivorship reported in zoo elephants. They have implications for improving captive working elephant management systems in range countries and for refining population viability analyses with realistic parameter values in order to predict future population size of the Asian elephant.
Highlights
Life-history analyses of captive animal populations are of both scientific and practical importance for species such as the Asian elephant (Elephas maximus) with a significant proportion of the world’s population living in captivity
Such estimates are much higher than the 10–15% first-year mortality reported for wild African elephants (Loxodonta africana) of Amboseli, Kenya [10,11], but no detailed data has been published of the underlying causes of such differences, or the correlates of varying neonatal or juvenile mortality rates in Asian elephants from the range states
Producing calves at short inter-birth intervals resulted in increased calf mortality risk, but this effect varied significantly according to the age of the calf (Table 3), so that the differences were largest during the first year of life
Summary
Life-history analyses of captive animal populations are of both scientific and practical importance for species such as the Asian elephant (Elephas maximus) with a significant proportion of the world’s population living in captivity. The limited published data on the age-specific levels of mortality from different captive populations are highly variable: while the first year mortality of intensively kept zoo elephants in North America [2] and Europe [6,7,8] is about 30%, first year mortality of timber camp elephants in South India was estimated at 24% for female and 16% for male calves [9] Such estimates are much higher than the 10–15% first-year mortality reported for wild African elephants (Loxodonta africana) of Amboseli, Kenya [10,11], but no detailed data has been published of the underlying causes of such differences, or the correlates of varying neonatal or juvenile mortality rates in Asian elephants from the range states.
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