Criteria for Gender and Age

Accurate classification of an animal’s gender and age is fundamental to wildlife research and management (Leopold 1933). Gender and age information is often used to establish harvest regulations and strategies, monitor a population’s demographic structure, health, and viability, and provide an understanding of behavioral ecology.

In many situations identifying an animal’s gender and age is relatively simple, especially for sexually dimorphic species and those with distinct age-specific patterns of appearance. However, accurate classification of an individual’s gender and/or age may be more complicated for species that are monomorphic. Additionally, for many species, young-of-the-year are identifiable, but differentiation among older age classes is difficult. Moreover, in many situations only partial information and/or material, such as a wing, jaw, or tooth, is available for evaluating an individual’s gender and/or age. This limitation can be exacerbated by the relatively short and/or sub-optimal time during which many samples are collected, such as during a hunting season.

One objective of this review is to describe basic techniques used to classify gender and age of birds and mammals that occur in North America. Techniques that have reduced subjectivity, improved accuracy, a wide range of applicability among numerous species, and a long history of standardized use are emphasized. The second objective is to identify techniques and resources used to examine particular species or groups of species. An exhaustive description of techniques used for evaluating gender and age for all species of interest cannot be achieved in this brief chapter. Consequently, we introduce some of the current techniques used and provide appropriate references for initiating detailed work.