Abstract
Individual age is an important element in models of population demographics, but the limitations of the methods used for age determination are not always clear. We used known-age data from moose (Alces alces), red deer (Cervus elaphus), semi-domestic reindeer (Rangifer tarandus tarandus) and Svalbard reindeer (Rangifer tarandus platyrhynchus) to evaluate the accuracy and repeatability of age estimated by cementum annuli analysis of longitudinally sectioned permanent incisors. Four observers with varying experience performed blind duplicate age estimation of 37 specimens from each cervid. The relationship between known age and estimated age was linear, except for Svalbard reindeer where a quadratic model gave a slightly better fit. After correcting for observer ID and animal ID, there was a slightly declining probability to assess the correct age with increasing age for moose, red deer and Svalbard reindeer. Across cervids and observers, estimated age equalled known age in 69% of all readings, while 95% age ± 1 year. Predicted probability of correct age assessment for experienced observers was 93% for red deer, 89% for Svalbard reindeer, 84% for moose and 73% for semi-domestic reindeer. Regardless of observer experience and cervid, there was a high agreement between repeated assessments of a given animal’s tooth sections. The accuracy varied between cervids but was generally higher for observers with former ageing experience with a given cervid. We conclude that the accuracy of estimated age using longitudinally sectioned incisors is generally high, and even more so if performed by observers with former ageing experience of a given species. To ensure consistency over time, a reference material from known-age individuals for each species analysed should be available for calibration and training of observers.
Highlights
In long-lived species, individual age is often a crucial component in analyses of population dynamics, phenotypic trait distribution, evolutionary ecology, and population management and conservation (Coulson et al 2006; Festa-Bianchet et al 2003; Gordon et al 2004; Pelletier et al 2012; Sæther et al 2013)
We explored to what extent accuracy was related to species, individual age and observer experience
Moose, red deer and Svalbard reindeer were marked as part of research projects, whereas the semidomestic reindeer were marked as part of reindeer husbandry management practices
Summary
In long-lived species, individual age is often a crucial component in analyses of population dynamics, phenotypic trait distribution, evolutionary ecology, and population management and conservation (Coulson et al 2006; Festa-Bianchet et al 2003; Gordon et al 2004; Pelletier et al 2012; Sæther et al 2013). Reliable methods for ageing of live and dead individuals are essential in many aspects of wildlife research and management. Teeth contain the most durable of all biological tissues (Lucas 2004), and due to their ability to conserve information related to key happenings in animals’ life histories The tooth root cementum is a mineralized tissue covering the root dentine surface and provides tooth attachment and maintenance of occlusal relationships as teeth wear (Bosshardt and Selvig 1997).
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