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Home / Equine Research Bank / PLoS One / Practical Bias Correction in Aerial Surveys of Large Mammals...
PloS one2016; 11(5); e0154902; doi: 10.1371/journal.pone.0154902

Practical Bias Correction in Aerial Surveys of Large Mammals: Validation of Hybrid Double-Observer with Sightability Method against Known Abundance of Feral Horse (Equus caballus) Populations.

Abstract: Reliably estimating wildlife abundance is fundamental to effective management. Aerial surveys are one of the only spatially robust tools for estimating large mammal populations, but statistical sampling methods are required to address detection biases that affect accuracy and precision of the estimates. Although various methods for correcting aerial survey bias are employed on large mammal species around the world, these have rarely been rigorously validated. Several populations of feral horses (Equus caballus) in the western United States have been intensively studied, resulting in identification of all unique individuals. This provided a rare opportunity to test aerial survey bias correction on populations of known abundance. We hypothesized that a hybrid method combining simultaneous double-observer and sightability bias correction techniques would accurately estimate abundance. We validated this integrated technique on populations of known size and also on a pair of surveys before and after a known number was removed. Our analysis identified several covariates across the surveys that explained and corrected biases in the estimates. All six tests on known populations produced estimates with deviations from the known value ranging from -8.5% to +13.7% and <0.7 standard errors. Precision varied widely, from 6.1% CV to 25.0% CV. In contrast, the pair of surveys conducted around a known management removal produced an estimated change in population between the surveys that was significantly larger than the known reduction. Although the deviation between was only 9.1%, the precision estimate (CV = 1.6%) may have been artificially low. It was apparent that use of a helicopter in those surveys perturbed the horses, introducing detection error and heterogeneity in a manner that could not be corrected by our statistical models. Our results validate the hybrid method, highlight its potentially broad applicability, identify some limitations, and provide insight and guidance for improving survey designs.
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Publication Date: 2016-05-03 PubMed ID: 27139732PubMed Central: PMC4854450DOI: 10.1371/journal.pone.0154902Google Scholar: Lookup
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  • Journal Article
  • Validation Study

Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

The article presents research on a novel method of estimating wildlife abundance through aerial surveying of large mammals, specifically feral horses. The researchers validate a hybrid technique combining two existing methods to address bias and improve accuracy in population size estimation.

Research Context

  • The research revolves around the crucial task of estimating wildlife abundance for effective management. Aerial surveys provide one of the only viable tools for acquiring such estimates for large mammal populations. However, these surveys are prone to detection biases that need to be addressed for the accuracy and precision of the estimates.
  • Until now, various methods for correcting aerial survey bias have been employed on large mammal species worldwide, but rarely have these techniques been validated rigorously.
  • Certain populations of feral horses in the western United States have been studied intensely, facilitating a rare opportunity to test aerial survey bias correction on populations with known abundance.

Hybrid Methodology for Bias Correction

  • The researchers hypothesized that a hybrid method, simultaneously employing double-observer and sightability bias correction techniques, would provide accurate estimations of population abundance. These techniques were validated on populations of known size and also on surveys conducted before and after a certain number of horses were removed.
  • It’s important to note that the double-observer technique involves independent observations from two observers, while sightability correction relies on the consideration of factors affecting the visibility of animals during aerial surveys.

Results and Findings

  • The analysis managed to identify various factors through the surveys that explained and corrected biases in the estimates. The resultant estimates deviated by -8.5% to +13.7% from the known number of horses, which were all well within <0.7 standard errors, indicating a high rate of accuracy.
  • However, the precision of the estimates varied widely, indicating a high level of variability in the results.
  • When surveys were conducted before and after known horse removals, the resultant change in population estimate was significantly larger than the known reduction, suggesting the introduction of more error.
  • The researchers suspect that the use of a helicopter for these surveys might have disturbed the horses, leading to detection error and non-uniform distribution which their statistical models couldn’t correct.

Conclusions and Insights

  • A key conclusion from this research is that the hybrid method of bias correction is validated and has potentially broad applicability, but does have certain limitations.
  • The study also provides valuable insights into factors that can affect accuracy and bias in aerial surveys, helping future researchers to optimize survey designs and methodologies for better precision and accuracy.

Cite This Article

APA
Lubow BC, Ransom JI. (2016). Practical Bias Correction in Aerial Surveys of Large Mammals: Validation of Hybrid Double-Observer with Sightability Method against Known Abundance of Feral Horse (Equus caballus) Populations. PLoS One, 11(5), e0154902. https://doi.org/10.1371/journal.pone.0154902

Publication

PloS one
ISSN: 1932-6203
NlmUniqueID: 101285081
Country: United States
Language: English
Volume: 11
Issue: 5
Pages: e0154902
PII: e0154902

Researcher Affiliations

Lubow, Bruce C
  • Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, Colorado, 80523, United States of America.
Ransom, Jason I
  • U.S. Geological Survey, Fort Collins Science Center, Fort Collins, Colorado, 80526, United States of America.

MeSH Terms

  • Air
  • Animals
  • Bias
  • Ecosystem
  • Horses
  • Population Density
  • Statistics as Topic / methods
  • Surveys and Questionnaires

Conflict of Interest Statement

The authors have declared that no competing interests exist.

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Citations

This article has been cited 1 times.
  1. Hennig JD, Schoenecker KA, Terwilliger MLN, Holm GW, Laake JL. Comparison of Aerial Thermal Infrared Imagery and Helicopter Surveys of Bison (Bison bison) in Grand Canyon National Park, USA.. Sensors (Basel) 2021 Jul 27;21(15).
    doi: 10.3390/s21155087pubmed: 34372324google scholar: lookup
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