Demographic Variables for Wild Asian Elephants Using Longitudinal Observations

Abstract

Detailed demographic data on wild Asian elephants have been difficult to collect due to habitat characteristics of much of the species’ remaining range. Such data, however, are critical for understanding and modeling population processes in this endangered species. We present data from six years of an ongoing study of Asian elephants (Elephas maximus) in Uda Walawe National Park, Sri Lanka. This relatively undisturbed population numbering over one thousand elephants is individually monitored, providing cohort-based information on mortality and reproduction. Reproduction was seasonal, such that most births occurred during the long inter-monsoon dry season and peaked in May. During the study, the average age at first reproduction was 13.4 years and the 50th percentile inter-birth interval was approximately 6 years. Birth sex ratios did not deviate significantly from parity. Fecundity was relatively stable throughout the observed reproductive life of an individual (ages 11–60), averaging between 0.13–0.17 female offspring per individual per year. Mortalities and injuries based on carcasses and disappearances showed that males were significantly more likely than females to be killed or injured through anthropogenic activity. Overall, however, most observed injuries did not appear to be fatal. This population exhibits higher fecundity and density relative to published estimates on other Asian elephant populations, possibly enhanced by present range constriction. Understanding the factors responsible for these demographic dynamics can shed insight on the future needs of this elephant population, with probable parallels to other populations in similar settings.

The importance of conflict-induced mortality for conservation planning in areas of human–elephant co-occurrence

“…Asian elephant densities vary considerably throughout their range, from as low as 0.25 elephants km À2 to >3 elephants km À2 , as used in this study (de Silva et al, 2013). Furthermore, some elephant populations may be less productive and have lower fecundity than that used to parameterize our model (de Silva et al, 2013); populations characterized by low fecundity may be rendered less resilient to HECm.…”

“…Furthermore, some elephant populations may be less productive and have lower fecundity than that used to parameterize our model (de Silva et al, 2013); populations characterized by low fecundity may be rendered less resilient to HECm. We tested the generality of our results by modeling elephant population dynamics under conditions of (a) lower density estimates, (b) lower fecundity estimates, and (c) a combination of lower density and lower fecundity.…”

Seasonality of reproduction in Asian elephantsElephas maximusand African elephantsLoxodonta africana: underlying photoperiodic cueing?

“… x = most conceptions take place; xx = conception peaks or increased number of females in oestrus; – = conceptions evenly distributed; light grey squares = rainy season; dark grey squares = resting time (Feb‐May; Mar ); n = number of observed births/matings/studied populations (– = number not indicated); Sources: *from timber working camps, + semi‐captive, italic = data limited; a De Silva et al. , b Santiapillai et al. , c Katugaha et al.…”

“…) or the long‐day period (De Silva et al. ), with the wet season in the short‐day period (Ishwaran ), or with the wet season in the long‐day period (Kurt , Katugaha et al. , Table ).…”

“… Sources: *from timber working camps, + semi‐captive, italic= data limited; a De Silva et al. , b Santiapillai et al. , c Katugaha et al.…”