The post hoc measurement as a safe and reliable method to age and size plethodontid salamanders

The worldwide biodiversity crisis with the resulting need to increase species protection has led researchers to pursue and select survey methods that guarantee the best quality of data and produce the least negative effects on wild animals. Plethodontids are the most diverse family of salamanders; all species are very sensitive to human handling and noninvasive, but accurate, measurement methods are needed to reduce researchers' impact. Here, we tested the reliability of a noninvasive post hoc method in estimating the snout-vent length (SVL) from photographs showing salamanders' dorsal view. The correlation between the estimated snout-vent length (SVL_e) and the conventional SVL was high (R ²  = .81), and no significant difference occurred between operators with different experience. Finally, we list the numerous advantages for the use of SVL_e in terms of data quality and in reducing the stress caused to wild animals.