How do I run a searcher efficiency trial at a wind farm?

A Searcher Efficiency (SE) trial measures the probability that an observer detects a carcass that is actually on the ground. You plant marked carcasses without the searchers knowing, then compare detections to plantings during the next scheduled search. The result is the searcher efficiency rate (p) that goes directly into the GenEst SE input file and into the final fatality estimate. Without it, every PCFM program is vulnerable to a regulator asking the obvious question: how many carcasses did you actually miss?

Thus, every PCFM study will need to conduct searcher efficiency trials to measure the proportion of carcasses missed by searchers and then apply the resulting searcher efficiency correction factor in the statistical estimates of total facility-generated fatality rates.

— IFC PCFM Handbook, §3.3.7.2

How an SE trial runs

  1. Plant blind. Place trial carcasses early in the morning before searchers arrive, so they do not see the placement. Searchers must be unaware of timing and location for the result to be valid.
  2. Mark each carcass discreetly so it is distinguishable from real fatalities (a short piece of electrical tape or clipped flight feathers is standard).
  3. Drop from waist height rather than placing on the ground, then record GPS location.
  4. Let the scheduled search run normally. Observers detect or miss each trial carcass.
  5. Check non-detections for availability. The trial administrator visits each undetected location to confirm the carcass was still present. Anything removed by scavengers is marked unavailable and excluded from the SE analysis.
  6. Record results on the SE Trial form (IFC PCFM Handbook Appendix G).

Sample size and where to run

The IFC PCFM Handbook is explicit that the SE rate has to be representative across the whole site and the whole season, not estimated from one corner of the project on one good day:

Searcher efficiency should be measured throughout the study period and over the entire spatial extent of the WEF to capture possible variation over time and space, for example, as a result of seasonal vegetation growth.

— IFC PCFM Handbook, §3.3.7.2

A minimum of 15 trial carcasses per season is the floor (20 or more recommended for scanning-style searches), with no more than two trial carcasses at a single turbine at any one time to avoid attracting scavengers and biasing CP results. In practice, this is where SE programs come apart: trials concentrated in one season, observers who notice disturbed vegetation, no visibility class on the form, and availability checks that never happen because the schedule lived in someone’s head.