Sampling strategies for species with high breeding-site fidelity: A case study in burrow-nesting seabirds

Woodworth

Fuller

et al. 2021

Ecol Sol and Evidence

1. Population estimates are commonly generated and used in conservation science.All estimates carry inherent uncertainty, but little attention has been given to when and how this uncertainty limits their use. This requires an understanding of the specific purposes for which population estimates are intended, an assessment of the level of uncertainty each purpose can tolerate, and information on current uncertainty.2. We conducted a review and meta-analysis for a widespread group of seabirds, the petrels, to better understand how and why population estimates are being used.Globally petrels are highly threatened, and aspects of their ecology make them difficult to survey, introducing high levels of uncertainty into population estimates.3. We found that by far the most common intended use of population estimates was to inform status and trend assessments, while less common uses were trialling methods to improve estimates and assessing threat impacts and conservation outcomes.4. The mean coefficient of variation for published estimates was 0.17 (SD = 0.14), with no evidence that uncertainty has been reduced through time. As a consequence of this high uncertainty, when we simulated declines equivalent to thresholds commonly used to trigger management, only 5% of studies could detect significant differences between population estimates collected 10 years apart for populations declining at a rate of 30% over three generations. Reporting of uncertainty was variable with no dispersion statistics reported with38% of population estimates and most not reporting key underlying parameters: nest numbers/density and nest occupancy. We also found no correlation between uncertainty in petrel population estimates and either island size, body size or species threat status -potential predictors of uncertainty. 6. Key recommendations for managers are to be mindful of uncertainty in past population estimates if aiming to collect contemporary estimates for comparison, to report uncertainty clearly for new estimates, and to give careful consideration to whether a proposed estimate is likely to achieve the requisite level of certainty for the This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Section: Discussionsupporting

confidence: 84%

Section: Introductionmentioning

confidence: 99%

Uncertainty in population estimates: A meta‐analysis for petrels

Woodworth

Fuller

et al. 2021

Ecol Sol and Evidence

“…Our findings support the conclusions of focussed single-species or regional studies that current approaches to repeat surveys are likely failing to detect changes and that only very large changes in population size can be detected reliably (Arneill et al, 2019;Hatch, 2003;D. R. Sutherland & Dann, 2012).…”

Section: Discussionsupporting

confidence: 83%

“…By clearly articulating their objectives for generating a population estimate, studies can determine the level of acceptable uncertainty (Possingham et al, 2012;Runge et al, 2011). For petrels, survey design will typically be constrained (Arneill et al, 2019), often by resources but also by logistics owing to other variables such as safety requirements or terrain limitations (Oppel et al, 2014). Given these constraints we caution that achievable levels of certainty around population estimates may inevitably be low.…”

Section: Are Population Estimates Always Warranted?mentioning

confidence: 99%

Uncertainty in population estimates: a meta-analysis for petrels

Woodworth²,

Fuller³

et al. 2021

Preprint

Population estimates are commonly generated and used in conservation science. All estimates carry inherent uncertainty, but little attention has been given to when and how this uncertainty limits their use. This requires an understanding of the specific purposes for which population estimates are intended, an assessment of the level of uncertainty each purpose can tolerate, and information on current uncertainty. We conducted a review and meta-analysis for a widespread group of seabirds, the petrels, to better understand how and why population estimates are being used. Globally petrels are highly threatened, and aspects of their ecology make them difficult to survey, introducing high levels of uncertainty into population estimates. We found that by far the most common intended use of population estimates was to inform status and trend assessments, while less common uses were trialling methods to improve estimates, and assessing threat impacts and conservation outcomes. The mean coefficient of variation for published estimates was 0.17 (SD = 0.14), with no evidence that uncertainty has been reduced through time. As a consequence of this high uncertainty, when we simulated declines equivalent to thresholds commonly used to trigger management, only 5% of studies could detect significant differences between population estimates collected 10 years apart for populations declining at a rate of 30% over three generations. Reporting of uncertainty was variable with no dispersion statistics reported with 38% of population estimates and most not reporting key underlying parameters: nest numbers/density and nest occupancy. We also found no correlation between population estimates and either island size, body size or species threat status - potential predictors of uncertainty. Synthesis and applications: Key recommendations for managers are to be mindful of uncertainty in past population estimates if aiming to collect contemporary estimates for comparison, to report uncertainty clearly for new estimates, and to give careful consideration to whether a proposed estimate is likely to achieve the requisite level of certainty for the investment in its generation to be warranted. We recommend a practitioner-based Value of Information assessment to confirm where there is value in reducing uncertainty.

“…However, for rare or highly localised species that can easily be missed within the landscape, they may result in low precision (Thompson 2013, Pacifici et al 2016). In such cases using prior knowledge such as historical records, pilot ground surveys and nocturnal surveys of aerial activity can improve results (Rayner et al 2007, Arneill et al 2019).…”

Section: Introductionmentioning

confidence: 99%

Detecting seabird responses to invasive species eradication

Ra²,

Terauds³

et al. 2021

Preprint

Maximising survey efficiency can help reduce the trade-off between spending limited conservation resources on evaluating performance of past interventions and directing those resources towards future interventions. Seabird responses to island eradications are often poorly evaluated owing to financial, logistical and methodological challenges associated with remote field work and species ecology. We surveyed an assemblage of threatened seabirds following the world's largest island eradication of multiple invasive species, testing multiple survey designs and outputs. We compared the outcomes of two important choices made during survey design: 1) whether to use unbiased or targeted surveys; and 2) implementing design-based or model-based analyses. An unbiased whole-island stratified randomised survey design performed well in terms of confidence in the final population estimates for widespread species, but poorly for localised recolonising species. For widespread species, model-based analyses resulted in slightly lower population estimates with narrower confidence intervals than traditional design-based approaches but failed to capture the realised niches of recolonising species, resulting in population estimates three orders of magnitude higher than current best estimates. We conclude that a multi-method approach to survey design best captures the size and distribution of recovering populations when the study system is ecologically diverse - importantly our results suggest there is no single strategy for efficient surveys of diverse seabird communities following large island invasive species eradications.