Determining the age classes of free-ranging female nilgai (Boselaphus tragocamelus) in southern Texas, USA

Age classification methods have not been evaluated for free-ranging nilgai antelope (Boselaphus tragocamelus) either on their native or introduced ranges of southern Texas, USA. Our objectives were to 1) determine if cementum annuli aging was a feasible method for aging nilgai, 2) measure the crown-lingual crest heights of nilgai molariform teeth to assess if these measurements were correlated to the cementum-annuli age of nilgai, and 3) develop nilgai age classes based on visual observations of tooth eruption and wear patterns. Six commercial nilgai meat harvests were conducted via helicopter from May–September 2018–2021 across 3 properties. We collected data from 225 harvested nilgai (n = 213 females and n = 12 juvenile males). We found significant relationships between cementum annuli ages and the crown-lingual crest heights of nilgai teeth (n = 63). However, the relationship was weak given the low R-squared values (0.23–0.46), suggesting that the age of female nilgai does not explain a large amount of variation among tooth heights (i.e., wear). From nilgai teeth samples, we documented 13 tooth eruption stages and 6 age classes. Female nilgai age classes presented provide land managers with the basic tools needed to assess population age structures. On the Indian subcontinent, our method could be used to evaluate age-biased predation on free-ranging nilgai.