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<p>Eurasian otters <i>Lutra lutra</i> are protected in Europe and vulnerable due to low reproductive rates. The ability to age cubs may be important to identify and protect breeding places and target seasonal surveys, yet little data exists. We developed a novel method to measure cubs relative to their mother using on-screen pixels on camera trap footage. We tested this on domestic ferrets <i>Mustela furo</i> of known length, then applied it to footage from an otter natal den to estimate relative growth curves of three litters from emergence (c. 2 months old) to beyond 7 months old. We tested inter-observer consistency, then developed some rule-of-thumb age-stage characteristics for cubs (&lt; 3 months, 3–6 months and 6–9 months). Absolute error relative to known tail to body length ratios of domestic ferrets was typically &lt; 10%, and better with good quality images. Linear sections of otter cub growth curves fitted the data reasonably (r<sup>2</sup> up to 0.36, <i>P</i> &lt; 0.001), particularly with good images, and coefficient of variation between observers averaged 5% for total length (body plus tail). Analyses of c. 3,000 otters killed on roads in Great Britain indicated that across the period from birth to adult, relative tail length remains relatively constant and cannot be used for ageing. Our study demonstrates that relative measurements using pixels are possible with a degree of accuracy sufficient to estimate otters cubs’ birth season. This opens the potential to study regionally specific breeding seasonality of otters from crowd-sourced video and photographs of families, potentially informing timing of surveys and reducing risk of disturbance.</p>

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Approximating the age of Eurasian otter (Lutra lutra) cubs from camera trap footage using proportional body measurements

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年7月21日

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  • Elizabeth M. Danes,
  • Elizabeth A. Chadwick,
  • Kirsten J. Oliver,
  • Melanie A. Findlay,
  • Patrick J. C. White

摘要

Eurasian otters Lutra lutra are protected in Europe and vulnerable due to low reproductive rates. The ability to age cubs may be important to identify and protect breeding places and target seasonal surveys, yet little data exists. We developed a novel method to measure cubs relative to their mother using on-screen pixels on camera trap footage. We tested this on domestic ferrets Mustela furo of known length, then applied it to footage from an otter natal den to estimate relative growth curves of three litters from emergence (c. 2 months old) to beyond 7 months old. We tested inter-observer consistency, then developed some rule-of-thumb age-stage characteristics for cubs (< 3 months, 3–6 months and 6–9 months). Absolute error relative to known tail to body length ratios of domestic ferrets was typically < 10%, and better with good quality images. Linear sections of otter cub growth curves fitted the data reasonably (r2 up to 0.36, P < 0.001), particularly with good images, and coefficient of variation between observers averaged 5% for total length (body plus tail). Analyses of c. 3,000 otters killed on roads in Great Britain indicated that across the period from birth to adult, relative tail length remains relatively constant and cannot be used for ageing. Our study demonstrates that relative measurements using pixels are possible with a degree of accuracy sufficient to estimate otters cubs’ birth season. This opens the potential to study regionally specific breeding seasonality of otters from crowd-sourced video and photographs of families, potentially informing timing of surveys and reducing risk of disturbance.