The present study aimed to conduct a comparative assessment of the external morphology, relative tail length and colour variation (RGB additive colour model) of Macaca munzala, Tawang and Macaca assamensis, Goalpara (southern Brahmaputra population), using a non-invasive photogrammetry method. The study revealed that the relative tail length of M. munzala (0.43 ± 0.03) is similar to that of M. assamensis assamensis, a subspecies of M. assamensis. On the other hand, the relative tail length of M. assamensis, Goalpara (0.61 ± 0.04) is similar to M. assamensis pelops, the other subspecies of M. assamensis. A total of 12 external morphological traits were observed and similarities found between the two studied populations. The study also found that the species-specific traits of M. munzala such as "dark patch of the crown whorl", "dark patch of hair at the temporal side", "spectacle appearance around eyes" and "whip-like tail appearance" in the infant and "stocky tail" are present in M. assamensis, Goalpara as well. Likewise, the "chin and cheek whiskers" are found in adult female individuals of both species. The comparative assessment of the dorsal coat colour (RGB value) revealed a darker brown dorsal coat in M. munzala (R 123.14 ± 11.62; G 107.71 ± 10.37, B 89.43 ± 9.21) than in M. assamensis, Goalpara (R 136 ± 23.57, G 112 ± 15.63, B 97.83 ± 13.04). The comparative assessment of facial skin colour among the adult individuals showed that the male M. munzala has darker brown facial skin than that of M. assamensis, whereas the female M. munzala shows darker reddish facial skin compared to M. assamensis, Goalpara. The species-specific traits of M. leucogenys were also compared, and the traits "chin and cheek whiskers", "darker dorsal coat" and "round penile" appearance have a striking resemblance to those of the M. munzala population of Tawang. Thus, the external morphological traits that are being used to distinguish these macaque species are highly variable even within the same species, and there is an urgent need to identify more precise species-specific morphological traits.

中文翻译：

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印度东北部Goalpara种群的Macaca munzala、Tawang和Macaca assamensis外部形态特征的比较评估

本研究旨在使用非侵入性摄影测量方法对 Goalpara（雅鲁藏布江南部种群）的 Macaca munzala、Tawang 和 Macaca assamensis 的外部形态、相对尾长和颜色变化（RGB 加色模型）进行比较评估。研究表明，M. munzala 的相对尾长 (0.43 ± 0.03) 与 M. assamensis assamensis 的尾长相似，M. assamensis assamensis 是 M. assamensis 的一个亚种。另一方面，M. assamensis Goalpara (0.61 ± 0.04) 的相对尾长与 M. assamensis pelops（M. assamensis 的其他亚种）相似。总共观察到 12 个外部形态特征，并在两个研究群体之间发现了相似之处。该研究还发现，M. munzala 的物种特异性特征，如“冠轮暗斑”、“ 还比较了 M. leucogenys 的物种特异性特征，“下巴和脸颊胡须”、“背毛颜色较深”和“阴茎圆形”外观与达旺的 M. munzala 种群的特征非常相似。因此，用于区分这些猕猴物种的外部形态特征即使在同一物种内也是高度可变的，因此迫切需要识别更精确的物种特异性形态特征。