Power to Detect Trends in Waterbird Abundance With Call-Response Surveys
Gibbs JP and Melvin SM. 1997. Power to Detect Trends in Waterbird Abundance With Call-Response Surveys. The Journal of Wildlife Management. 61(4):1262-1267
We broadcast calls of grebes, rails, and bitterns, and passively counted other species, along 36 survey routes in Maine wetlands during 1989-92. Our objectives were to determine the magnitude and temporal variation in waterbird call-response rates, and to estimate, through computer simulation, the statistical power of variously configured monitoring programs. Average call-response rates on survey mini-routes ranged from 2.8 to 6.0 responses per 10-station mini-route, and temporal variation in counts was relatively high (CV in all species >80%). A power analysis, performed by coupling Monte Carlo methods with linear regression, indicated that changes in call-response rates of 10% would be difficult to detect over a 10-year monitoring period in any species. Changes of 25%, however, could be detected reliably (P > 0.90) by surveying 40-80 mini-routes on 2-3 occasions annually. Passive counts at call-response stations yielded useful abundance information on many wetland species currently undersampled by existing avian monitoring schemes. We conclude that call-response surveys for selected species, coupled with passive counts of other species, are a logistically feasible and statistically defensible means of monitoring trends in regional populations of wetland birds.
- Type
- Journal Article
- Authors
- Gibbs, James; Melvin, Scott
- Units
- SODN
- Keywords
- American Bittern, Botaurus Lentiginosus, Maine, Pied-Billed Grebe, Podilymbus Podiceps, population surveys, Porzana Carolina, power analysis, Rallus Limicola, sora, Statistical Power, Virginia Rail, Waterbirds, Wetland Birds