How many are there?
Density proxy
Density goes a step further: how many animals are there? When recorders are synchronised in time, one call reaches each of them a fraction of a second apart, and those differences show where the caller was.
How it works
Locating calls lets us tell individuals apart instead of counting calls, which one loud bird can inflate. The result is a minimum count of calling individuals and how they are spread across the area, which can be compared over time.
What you get
- Minimum number of distinct calling individuals
- Where they are, as a density map
- Trends when the survey is repeated
Good for
- Territorial species that call regularly
- Measuring how a population responds to management
- Long-term monitoring of key species
Study design
Needs clusters of time-synchronised recorders spaced closely enough that several hear the same call.