Table 1.
Descriptive statistics of the data used in the analyses (stillbirth and liveborn survival models) of Asian elephants illustrating the sample size and data completeness.
Figure 1.
The probability of stillbirth according to maternal age at the birth of calf in Asian elephants.
The probability of stillbirth increased significantly with maternal age especially after age 35 (n = 1020 births). Figure shows predicted values and 95% confidence intervals from the model.
Figure 2.
Overall survival distribution function of Asian elephants from birth to age 18 (A) and correlates of mortality of liveborn calves from birth to age of 5 (B–D) (Table 3).
The mortality risk was highest during the first two years of calf life, and rose again between ages four and five (B). Calves born to older mothers had an increased probability of death irrespective of their own age (C) and short inter-birth interval put calves to higher risk of dying during their first two years of life (previous birth interval and calf age interaction, D). The sample size to which the discrete time survival analysis (B–D) was based was 975 calves with total of 4121 observations and correlated terms also included calf sex, birth order, birth cohort and repeated terms of the same mother and living area (mother id and mother area, see Methods and Table 3). Each year of calf age (1–5) illustrates the probability of dying within the previous full year (B,D, see Methods). The classification of inter-birth interval to first born, short, medium and long was based on the distribution of the birth interval length in the population and to 25% and 75% quartiles (D, see Methods). Figures show predicted values and 95% confidence intervals (B,C) from the model.
Table 2.
Mortality of Asian elephant calves by each age group from birth to age of 5 years.
Table 3.
Discrete time survival model of the Asian elephant calf mortality risk from birth to 5 years (n = 975 calves with 4121 observations (227 deaths)).
Table 4.
Death causes of Asian elephant calves dying before age 5 by sex and age group (n = 224).