How often should carcass searches be conducted around wind turbines?

Q: How often should carcass searches be conducted around wind turbines?

The IFC PCFM Handbook recommends a 7-day search interval as the First Year default for all carcass size classes, then tuning the interval in subsequent years against site-specific carcass persistence results. Smaller and faster-decomposing carcasses require shorter intervals; longer intervals systematically undercount fatalities.

Search interval is the single biggest lever a wind farm operator has on detection probability. Every extra day between visits is another day for carcasses to decompose, get scavenged, or be removed by farm operations before they can be counted, which biases the final fatality estimate downward. The IFC PCFM Handbook is direct about the relationship:

Shorter search intervals result in fewer opportunities for carcasses to decompose or be removed by scavengers before searchers can find them, increasing detection probability and fatality estimate precision.

— IFC PCFM Handbook, §3.3.6.1

First Year vs. Subsequent Years

Phase	Interval	Rationale
First Year design	7 days for all size classes	Persistence is unknown in advance; 7 days is a defensible generalized starting point
Subsequent Years	Tightened or relaxed against Year 1 CP data	Tighten where small-carcass persistence is short; relax where large-carcass persistence is long

Why interval depends on carcass size

Persistence times differ dramatically between size classes. Bat carcasses can disappear in days; large birds may persist much longer. A search interval set for raptor monitoring will systematically miss bats:

Smaller carcasses tend to be removed more quickly than larger carcasses and therefore require a shorter (more frequent) search interval.

— IFC PCFM Handbook, §3.3.6.2