How Big Is It Really? Assessing the Efficacy of Indirect Estimates of Body Size in Asian Elephants

Abstract

Information on an organism’s body size is pivotal in understanding its life history and fitness, as well as helping inform conservation measures. However, for many species, particularly large-bodied wild animals, taking accurate body size measurements can be a challenge. Various means to estimate body size have been employed, from more direct methods such as using photogrammetry to obtain height or length measurements, to indirect prediction of weight using other body morphometrics or even the size of dung boli. It is often unclear how accurate these measures are because they cannot be compared to objective measures. Here, we investigate how well existing estimation equations predict the actual body weight of Asian elephants Elephas maximus, using body measurements (height, chest girth, length, foot circumference and neck circumference) taken directly from a large population of semi-captive animals in Myanmar (n = 404). We then define new and better fitting formulas to predict body weight in Myanmar elephants from these readily available measures. We also investigate whether the important parameters height and chest girth can be estimated from photographs (n = 151). Our results show considerable variation in the ability of existing estimation equations to predict weight, and that the equations proposed in this paper predict weight better in almost all circumstances. We also find that measurements from standardised photographs reflect body height and chest girth after applying minor adjustments. Our results have implications for size estimation of large wild animals in the field, as well as for management in captive settings.

Weigh and see—Body mass recordings versus body condition scoring in European zoo elephants (Loxodonta africana and Elephas maximus)

“…(c) Body mass growth curves for male E. maximus . Our data for European zoo elephants (a and a′) in black and literature data for (semi‐)captive males in gray (b and b′: Sukumar et al, ; c: Kurt & Kumarasinghe, [semi‐captive]; d: Chapman et al, ; e: Kurt & Kumarasinghe, [captive] and f: Weihs et al, ). a′ indicates data based on at least three body masses per 3 months.…”

“…Our data for European zoo elephants (a and a′) and reported curves for females in (b) one North American zoo (Fischer et al, ), respectively, four European facilities (c) by Kurt and Kumarasinghe (). Literature data for semi‐captive populations are given in gray (d: Sukumar et al, ; e: Kurt & Kumarasinghe, ; f: Chapman et al, ; g: Weihs et al, ). a′ indicates data based on at least three body masses per three months.…”

“…Due to their sheer size and mass, weighing is a challenging task for elephant‐keeping facilities (Wijeyamohan et al, ). Thus, alternative monitoring methods like visual BCS or BM calculation from morphometric measurements have been developed and validated to varying degrees (reviewed in Chapman et al, ; Schiffmann, Clauss, Hoby, & Hatt, ). Probably due to these challenges, comprehensive BM data over the course of time for individual zoo elephants are scarce and typically limited to narrow periods of an elephant's life (Fischer et al, ; Lang, ; Miller & Andrews, ; Schwammer et al, ).…”

“…Probably due to these challenges, comprehensive BM data over the course of time for individual zoo elephants are scarce and typically limited to narrow periods of an elephant's life (Fischer et al, ; Lang, ; Miller & Andrews, ; Schwammer et al, ). According to our knowledge, investigations on the correlation of results of weighing, which is considered the gold standard for BM monitoring as opposed to extrapolations from morphometrics (Chapman et al, ), and BCS have not been conducted in a comprehensive sample of zoo elephants yet. It is the objective of this report to assess the relationship of these methods and to derive recommendations regarding their applicability with respect to an elephant's life stage.…”

Taking the Elephants' Perspective: Remembering Elephant Behavior, Cognition and Ecology in Human-Elephant Conflict Mitigation

“…We propose to address these questions using two complementary areas of research: the study of elephant behavior and cognition, and the study of elephant ecology and life history. Studies conducted both in Africa and Asia, with both captive and wild populations, show clear evidence for individual differences in a number of ecological and cognitive categories, including parasite load (Lynsdale et al, 2017), body size (Evans and Harris, 2012;Chapman et al, 2016), primiparity (Crawley et al, 2017), social hierarchy (McComb et al, 2011), innovation (Bates et al, 2008b), cooperation (Plotnik et al, 2011), problem-solving (Foerder et al, 2011), aggression (Poole, 1989), and personality (Lee and Moss, 2012;Yasui et al, 2012;Seltmann et al, 2018). Identifying whether or not specific behavioral, physical, demographic or personality traits (collected through future ecological, ethological and experimental research on captive and wild elephants) correlate with an elephant's propensity to crop-raid or engage in conflict may have important implications for preventing or managing these conflicts across different landscapes.…”