Currently, 3 Coefficient of Variation tools are available:

• Amphibian Count CV Tool. A total of 47 studies has yielded 212 separate count series for 54 amphibian species.
• Breeding Bird Density CV Tool. Included are data from a total of 105 study plots, yielding 3663 separate count series for 335 bird species.
• Bird Point Count CV Tool. Included are data from a total of 4974 routes, yielding 301342 count series for 646 bird species.

These tools are designed to help land managers and others set sample size for monitoring programs. Seeing how variable a particular taxonomic group is (along with other variables such as geographic area, sex/age class, etc.) can help determine the sample size you should set when monitoring that taxonomic group.

Sample size has a lot to do with whether or not a monitoring program will detect population trends (should they exist) over time. Variance in counts of animals over space and time is the major determinant of how many samples are needed for a program to be effective. Obtaining a good estimate of variability for a particular species at a given place under a given sampling regime requires several years of pilot study data. Short of that, you might cast around for estimates from other studies for a rough place to start (with plans to refine your protocol once your data is in). That's the idea behind these searchable databases: to organize existing data.

A coefficient of variation (CV) is calculated by dividing the standard deviation by the mean. See how the CV is calculated, step by step. To account for the effects of trend over time, which elevates variation in counts, we used the standard deviation of the residuals from a regression of the counts run against time. Associated with this method are inherent assumptions which you may find disagreeable due to sticky statistical issues like model misspecification, autocorrelation, and effect of survey length on variance. For this reason, we provide the raw counts so you can analyze the data using your preferred method.