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<p>Accurate bird density estimates are essential for conservation planning and understanding ecological dynamics within forest ecosystems. South Africa’s forest avifauna, though limited in range, comprises species of high conservation concern, yet recent, robust population estimates are lacking. We addressed this gap by conducting surveys across key forest biomes in South Africa using both Distance Sampling (DS) and Fixed Radius Counts (FRC), supplemented with a trait-based predictive model. Initial DS surveys in the dense Afrotemperate forests of the Western Cape frequently yielded inflated density estimates because of the challenges of applying DS assumptions in visually obstructed habitats. By incorporating temporal truncation and ecological judgment, we refined these estimates to align with expected species behaviours and ecological plausibility, using the results to create a predictive model. The trait-based model, informed by species’ functional traits and environmental variables, provided a valuable validation method and was extended to assess density estimates for broader forest avifauna, including species of conservation concern. Comparisons between DS, FRC, and model-predicted densities revealed the limitations and strengths of each method, with recommendations for their application in diverse forest environments. This integrated approach offers a pathway to more reliable bird population estimates, essential for effective conservation management in South Africa’s threatened forest biomes. It further allows the estimation of population densities from non-DS surveys. Species density estimates ranged from &lt; 1 to &gt; 100 individuals/km<sup>2</sup>, with FRC and trait-based predictions generally producing more ecologically plausible values than uncorrected DS, particularly in complex forest habitats.</p>

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Comparative density estimates of South Africa’s forest birds: integrating distance sampling, fixed radius counts, and trait-based predictive models

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年12月29日

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  • Alan T. K. Lee,
  • David A. Ehlers Smith,
  • Jessica Leaver,
  • Nasiphi Bitani,
  • Jake Mulvaney,
  • Colleen T. Downs

摘要

Accurate bird density estimates are essential for conservation planning and understanding ecological dynamics within forest ecosystems. South Africa’s forest avifauna, though limited in range, comprises species of high conservation concern, yet recent, robust population estimates are lacking. We addressed this gap by conducting surveys across key forest biomes in South Africa using both Distance Sampling (DS) and Fixed Radius Counts (FRC), supplemented with a trait-based predictive model. Initial DS surveys in the dense Afrotemperate forests of the Western Cape frequently yielded inflated density estimates because of the challenges of applying DS assumptions in visually obstructed habitats. By incorporating temporal truncation and ecological judgment, we refined these estimates to align with expected species behaviours and ecological plausibility, using the results to create a predictive model. The trait-based model, informed by species’ functional traits and environmental variables, provided a valuable validation method and was extended to assess density estimates for broader forest avifauna, including species of conservation concern. Comparisons between DS, FRC, and model-predicted densities revealed the limitations and strengths of each method, with recommendations for their application in diverse forest environments. This integrated approach offers a pathway to more reliable bird population estimates, essential for effective conservation management in South Africa’s threatened forest biomes. It further allows the estimation of population densities from non-DS surveys. Species density estimates ranged from < 1 to > 100 individuals/km2, with FRC and trait-based predictions generally producing more ecologically plausible values than uncorrected DS, particularly in complex forest habitats.