Forensic Identification of Confiscated Helmeted Hornbill (Rhinoplax vigil) Casques and Implications for Individual Quantification in Wildlife Crimes

Abstract

In wildlife forensic practice, species identification and estimation of the Minimum Number of Individuals (MNI) for highly processed specimens have long relied on weight-based conversion methods, which may result in underestimation of the number of individuals involved in a case. Focusing on 41 confiscated casque products of the helmeted hornbill (Rhinoplax vigil), including 32 newly added Tianjin samples, this study combines macroscopic morphological examination with mitochondrial DNA barcoding (16S rRNA, COI, and Cytb) to explore a more robust approach for individual quantification. The results demonstrate that the conventional "weight-based" approach overlooks critical biological information contained in anatomical structures and cannot accurately reflect the actual number of individuals involved. Based on this, we propose an anatomy-based criterion centered on the principle of structural uniqueness: specimens retaining biologically unique beak or casque structures should be directly assigned to a single individual, whereas weight-based estimation should only be applied when original anatomical features are entirely absent. In addition, based on morphometric calibration using a larger sample size (n = 40), we propose updating the reference benchmark for estimating the number of individuals in heavily processed solid casque products from 86 g to 65 g. This approach improves the scientific rigor and accuracy of forensic identification and provides reliable technical support for the conviction, sentencing, and law enforcement of wildlife trafficking cases involving helmeted hornbill and other endangered species.