Ageing, Sexing, and Geographic Provenance of Specimens

Ectotherms (animals whose body temperature follows the environment) grow rapidly in warm, food-rich seasons and slow or stop in cold or dry seasons. That rhythm is inscribed in bone as alternating zones of dense and less dense cortical tissue. A cross-section cut from the femur or tibia of a tortoise, stained with haematoxylin and eosin and examined under a light microscope, shows these rings as dark and light bands. Counting the dark bands gives the number of slow-growth seasons the animal lived through, which translates to a biological age estimate.

The technique is most widely applied to traded tortoise species (Testudo, Geochelone) and to sea turtles, where it helps establish whether a traded specimen is a juvenile harvested from the wild or an adult bred in captivity. In fish, otoliths (ear stones) are the preferred skeletochronological structure: daily and annual rings in otoliths can be counted to give age in years and, at fine resolution, in days.

Grazing and browsing mammals wear their teeth against abrasive plant material throughout their lives. This wear follows a predictable trajectory within a species, which allows an experienced examiner to assign an age class from the degree of molar occlusal surface wear. The method has been refined for African ungulates (buffalo, kudu, impala, elephant, zebra) through large datasets of known-age animals.

In practice, courts accept dental age estimates as expert opinion evidence in classes (juvenile/sub-adult/adult/aged) rather than as precise years. The value in a CITES case is often binary: was this animal a juvenile, suggesting it was recently taken from the wild, or an adult consistent with pre-ban stock? A juvenile designation defeats a claim of legal antique status and supports a recent wild-take conclusion.

Elephant tusks (upper second incisors) grow continuously through the animal's life. Bull elephants grow larger tusks than cows, and growth rate varies between African populations. Long-term studies at Amboseli National Park in Kenya and at Kruger National Park in South Africa have accumulated data on tusk mass and length in marked, known-age animals, producing sex-specific weight-age regression curves.

Given a tusk's weight and length and the sex of the animal (determined from DNA if the skull is absent), an investigator can estimate the probable age of the animal at death within a range of roughly plus or minus five years. A pair of tusks with a combined mass of 60 kg, from a bull, suggests an animal aged 45-55 years. Such a large, old bull is implausible as a captive-bred animal, which supports a wild-caught conclusion. The method's limitations include population-level variation in tusk growth and the absence of weight-age curves for Central and West African forest elephant (Loxodonta cyclotis) populations.

Raptors and many other birds moult their flight feathers in a predictable sequence over two to four years, replacing juvenile feathers with adult plumage in stages. For species with distinct juvenile and adult feather morphologies (e.g. many eagle species), the mix of old and new feathers on a seized live bird, or on a bird skin, indicates which moult cycle the bird is in, narrowing its age to a range within two to three years.

In species where captive breeding is claimed (African grey parrots, hyacinth macaws, many raptors), feather moult analysis helps distinguish wild-caught from captive-bred birds. Captive birds often show aberrant moult sequences, stress lines (fault bars) in feather vanes from nutritional or health stresses during feather growth, and plumage characteristics inconsistent with the claimed hatch date. A wildlife ornithologist examining feathers alongside DNA and isotope evidence can build a combined age-and-origin profile that is difficult to defeat in court.

Sex determination matters in CITES cases because some quota systems apply sex-specifically (a bull elephant quota is separate from a cow quota), and because morphological sex characteristics used by traffickers to document specimens can be faked. Genetic sex determination from tissue, blood, or feathers provides an objective result that is independent of morphology.

• Mammals: PCR amplification of the SRY gene (Y chromosome-specific) confirms male sex when present. A negative SRY result in adequate-quality DNA is consistent with female sex but requires a positive female sex marker for confirmation. Amelogenin locus (AMELX/AMELY) provides a size-difference assay that is informative in many mammal species.
• Birds: birds use ZW (female) / ZZ (male) sex determination. The CHD (chromo-helicase-DNA-binding) gene on the W and Z chromosomes produces amplicons of different sizes in a PCR assay; females (ZW) give two bands, males (ZZ) give one. The assay works from blood, feather pulp, and dried museum specimens.
• Reptiles: sex determination in reptiles is more complex because many species have temperature-dependent sex determination and lack sex chromosomes. Genetic sexing is possible in species with sex chromosomes (some geckos, pythons). In species without, histological gonadal examination from preserved tissue remains the most reliable method.

Geographic provenance is the most technically complex dimension of wildlife specimen analysis, and also the most legally significant: it narrows the legal origin claim and, in ivory cases, directly addresses the pre-/post-ban legal threshold. Three independent methods are available, and their combination is stronger than any single one.

• Population genetic assignment: microsatellite or SNP profiles from ivory, horn, or tissue are compared to reference databases (e.g. the Elephant Genomics Project's >2000 African elephant reference samples). Assignment algorithms estimate the probability that the specimen's genotype comes from each sampled population, narrowing its origin to a region. Research using reference databases of African elephant genotypes has placed ivory consignments within specific savanna regions with high accuracy.
• Stable isotope analysis: strontium-87/86 ratios in bone and ivory reflect local bedrock geology; oxygen-18/16 ratios reflect local precipitation chemistry. Animals living on old Precambrian shield geology (central and eastern Africa) have different strontium signatures from animals on younger volcanic geology (East African Rift). Carbon-13/12 ratios in tusk collagen distinguish C3 (forest) and C4 (savanna) diets, with forest elephants occupying a distinct isotope space from savanna elephants.
• Radiocarbon dating: the atmospheric nuclear testing of 1955-1963 produced a distinctive spike in atmospheric C-14 that has been declining at a known rate since. The Suess bomb-curve calibration allows ivory or tissue formed after 1955 to be dated to within one to two years using accelerator mass spectrometry. A tusk dated to a formation period of 2008 cannot be pre-ban stock regardless of any document that claims otherwise.