Visually estimating body mass of wild pigs

Area of Science:

• Wildlife Ecology and Management
• Invasive Species Biology
• Animal Physiology and Biometrics

Background:

• Wild pig (Sus scrofa) body mass is crucial for assessing population health, reproductive capacity, and resilience of this invasive species.
• Accurate body mass data is vital for effective management, but traditional weighing methods are often impractical in the field.
• Visual estimation of wild pig body mass is a potential alternative, but its accuracy and influencing factors require investigation.

Purpose of the Study:

• To evaluate the accuracy of visual body mass estimation in wild pigs.
• To identify demographic and morphometric factors influencing the accuracy of visual mass estimates.
• To provide recommendations for improving visual body mass estimation in wild pigs for management purposes.

Main Methods:

• Visual body mass estimates were collected for 1,210 wild pigs across five regions (Alabama, Texas, Hawaii, Guam, Queensland).
• Actual weights were recorded, alongside morphometric measurements and age data for each animal.
• Statistical analysis was performed to determine the correlation between estimated and actual weights, and the influence of age and morphometrics.

Main Results:

• Overall, visual estimates were highly accurate, with an average underestimation of only -0.14 kg.
• Estimates were significantly underestimated for younger wild pigs (<1-3 years) that were heavier (>30 kg), with errors up to -20 kg.
• Wild pigs continued to grow in length, height, and girth with age, impacting visual estimation accuracy, particularly for stout, younger individuals.

Conclusions:

• Visual body mass estimation can be a reliable tool for wild pigs, but age-related morphological differences must be considered.
• Underestimation of younger, heavier wild pigs can misinform crucial population management decisions regarding reproductive capacity.
• Regular observer calibration and incorporating age indicators (e.g., morphological proportions) are recommended for accurate visual mass estimation.