Monitoring Whooping Crane Abundance Using Aerial Surveys: Influences on Detectability

Area of Science:

• Wildlife Biology
• Conservation Science
• Ornithology

Background:

• Traditional aerial surveys for endangered whooping cranes (Grus americana) since 1950 have known limitations.
• Existing methods raise questions about efficacy, defensibility, repeatability, and future utility for conservation.
• Improved and standardized monitoring techniques are crucial for effective population management.

Purpose of the Study:

• To assess the efficacy of line transect-based distance sampling for aerial surveys of whooping cranes.
• To evaluate factors influencing detectability, including observer experience, sun position, distance, and group size.
• To inform the design and implementation of future whooping crane monitoring efforts.

Main Methods:

• Conducted a preliminary distance sampling test during the 2010-2011 winter survey.
• Utilized an experimental decoy survey to systematically assess detectability variables.
• Analyzed impacts of observer experience, sun angle, distance from transect, and group size on detection rates.

Main Results:

• Preliminary distance sampling indicated a detectability of 0.558 within 500m of transects.
• Decoy detectability increased with group size and showed a quadratic relationship with distance.
• Detectability was significantly higher with sun overhead (2.7x) or at observer's back (3.9x) compared to in eyes; inexperienced observers misclassified targets more often.

Conclusions:

• Line transect distance sampling shows promise for improving whooping crane aerial surveys.
• Observer experience and environmental conditions like sun position critically affect detection accuracy.
• Understanding these factors is essential for refining survey protocols and ensuring reliable population estimates.