# Body Mass Records of Zoo‐Managed Rhinoceros (Ceratotherium simum, Diceros bicornis, Rhinoceros unicornis) as Compared to Field Data of Free‐Ranging Specimens

## TL;DR

Zoo-managed rhinos, especially female white rhinos, are often heavier than their wild counterparts, possibly due to diet and environment differences.

## Contribution

This study compares zoo and wild rhino body mass data, revealing systematic differences in female white rhinos.

## Key findings

- Female white rhinos in zoos are heavier than free-ranging females.
- Zoo rhinos do not show seasonal body mass fluctuations due to consistent food supply.
- Obesity is not a population-level issue in black or greater one-horned rhinos.

## Abstract

The body mass of zoo animals may differ from those in wild populations due to the different environmental and dietary conditions being offered under human‐managed care. These differences in body mass may impact health at both individual and population levels. In the case of rhinoceroses, this is relevant because of the distinct feeding requirements of each species and their susceptibility to obesity when inappropriate diets are offered. Here we attempt a comparison between the adult body mass records of the global zoo populations of rhinoceroses (white Ceratotherium simum, black Diceros bicornis, and greater one‐horned Rhinoceros unicornis) and the available body mass records of free‐ranging specimens in the literature. Body mass data from free‐ranging specimens is surprisingly scarce for white and greater one‐horned rhinos. Most adult zoo rhinoceroses are within the body mass range described for wild populations except female white rhinoceroses, which are, on average, heavier than free‐ranging females. Also, contrary to what has been described for natural habitats, zoo rhinoceroses do not show evidence for seasonal fluctuations in body mass, most likely due to the consistent nutrient supply in zoos. While obesity might be present across female white rhinos, and exacerbate other underlying health issues at the individual level in other taxa, this particular data set does not provide evidence that obesity is a population‐level phenomenon in black or greater one‐horned rhinos. Our findings should not weaken the efforts towards improving zoo rhinoceros nutrition and body condition monitoring.

Female white rhinos in zoos systematically exceed the body mass range for free‐ranging specimens; this is not the case in black rhinos.

Original body mass data for free‐ranging white and greater one‐horned rhinos is scarce.Compared to free‐ranging conspecifics, female white rhinos in zoos are possibly overweight.For male white rhinos, black rhinos of both sexes, and female greater one‐horned rhinos, zoo weights do not differ systematically from free‐range data.

Original body mass data for free‐ranging white and greater one‐horned rhinos is scarce.

Compared to free‐ranging conspecifics, female white rhinos in zoos are possibly overweight.

For male white rhinos, black rhinos of both sexes, and female greater one‐horned rhinos, zoo weights do not differ systematically from free‐range data.