Estimating the proportion of uncatchable animals in a population by double-sampling

Area of Science:

• Ecology
• Wildlife Biology
• Population Dynamics

Background:

• Capture-recapture methods are standard for estimating animal population sizes.
• These methods typically only account for the catchable segment of a population, potentially leading to underestimation.
• The presence of uncatchable individuals is a known limitation in ecological surveys.

Purpose of the Study:

• To develop and present novel statistical estimators for the proportion of uncatchable animals within a population.
• To provide a method for correcting population size estimates derived from capture-recapture data to account for uncatchability.
• To demonstrate the practical application of these estimators using real-world ecological data.

Main Methods:

• The study proposes two closed-form maximum likelihood estimators.
• These estimators rely on dual sampling of the proportion of marked animals.
• Sampling involves distinct draws from catchable-only and mixed (catchable and uncatchable) animal groups, with specific conditions on sample availability and subpopulation size.

Main Results:

• The presented estimators provide a quantitative measure of the uncatchable proportion of a population.
• Successful correction of population size estimates for uncatchability is demonstrated.
• The methodology is validated using data from a study on eider ducks.

Conclusions:

• The developed estimators offer a significant advancement in accurately assessing total population sizes.
• Ecological studies using capture-recapture can be enhanced by incorporating corrections for uncatchable individuals.
• This approach improves the reliability of wildlife population estimates in ecological research.