Compare two survey counts with explicit observation effort.
Compare species counts across two visits and normalise each visit to observations per hour. Enter zero only when that species was checked and not recorded.
Rate = count × 60 ÷ visit effort in minutes. Rate difference = B − A; percent change = (B rate − A rate) ÷ A rate × 100 and is undefined when A is zero. Elapsed survey time is used, not observer-hours. Counts can reflect detectability, weather, method and repeat sightings. Effort correction alone cannot establish abundance or population change. Record comparable methods and list only species you checked in both visits. See eBird’s explanation of survey protocols and effort.
Entered observation and deployment dates support 1900–2100. These tools use the local dates you enter; they do not infer time zones or submit records to a monitoring programme.
Instructions
- Fill Visit effort and context for visits A and B, then select Apply visit details.
- Enter Species or description with Count in visit A and Count in visit B.
- Select Add record for each species checked in both visits.
- Compare the rates, then use Export CSV, Download text or Print results.
Understanding your results
Six observations in 30 minutes and twelve in 60 minutes both give 12 per hour. This corrects for elapsed time only. It does not account for weather, visibility, observer skill or repeat sightings, so a rate change cannot establish a population change.
What to do if percentage change is undefined
The percentage needs a nonzero rate in visit A. A zero baseline cannot support a percentage increase; read the count and rate difference instead. Check that zero means the species was checked and not recorded, rather than missing survey information.
Using this tool in your browser
These entries are handled in your browser. Saving is off by default; enable the storage checkbox to retain this tool’s records on this device. Other people using the same browser may see them. Clearing site data removes the saved copy. Export a separate backup before changing devices or resetting entries.
Summary
Compare like methods and retain the effort and conditions alongside the counts.