Title: Fixed-Radius Point Counts in Forests: Factors Influencing Effectiveness and Efficiency
Author: Petit, Daniel R.; Petit, Lisa J.; Saab, Victoria A.; Martin, Thomas E.;
Source: In: Ralph, C. John; Sauer, John R.; Droege, Sam, technical editors. 1995. Monitoring bird populations by point counts. Gen. Tech. Rep. PSW-GTR-149. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: p. 49-56
Publication Series: General Technical Report (GTR)
Description: The effectiveness of fixed-radius point counts in quantifying abundance and richness of bird species in oak-hickory, pine-hardwoods, mixed-mesophytic, beech-maple, and riparian cottonwood forests was evaluated in Arkansas, Ohio, Kentucky, and Idaho. Effects of count duration and numbers of stations and visits per stand were evaluated in May to July 1991 by conducting approximately 1000 50-m (or 40-m) fixed-radius point counts. Most (>60 percent) species and individuals were detected in the first 4 minutes of the 8-minute counts, although accumulation did not cease even after extended 10-and 20-minute counts. Because of the tradeoff between count duration and number of stations that can be visited in a given period of time, counts of 6 minutes may be most appropriate for monitoring programs where maximizing number of individuals detected is important. Six stations within stands of eastern deciduous forest and 15 stations in riparian cottonwood fragments did not appear to completely document the bird community within those tracts. A single visit detected approximately 70 percent, and two visits 90 percent, of the species recorded after three repeated visits to a stand. Thus, two visits to a tract (or a single 20-minute count) may be necessary to ensure a relatively complete species list. Estimates of relative abundance from a single visit to a stand were highly correlated with cumulative estimates obtained after three visits for relatively common migratory, but not resident, species. In general, shorter count durations, fewer stations, and fewer visits were required to effectively sample migrants, as compared to residents. A greater number of stations are probably necessary when using fixed-radius compared with unlimited-distance counts because fewer individuals are detected in small, fixed-radius plots. Conversely, fixed-radius point counts provide a number of important advantages over unlimited-distance point counts in comparisons of relative abundances among habitats and sites. Moreover, fixed-radius plots may allow for greater flexibility in study design and also for better resolution of bird-habitat relationships because of the physical proximity between bird and habitat measurements.
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Petit, Daniel R.; Petit, Lisa J.; Saab,Victoria A.; Martin, Thomas E. 1995. Fixed-Radius Point Counts in Forests: Factors Influencing Effectiveness and Efficiency. In: Ralph, C. John; Sauer, John R.; Droege, Sam, technical editors. 1995. Monitoring bird populations by point counts. Gen. Tech. Rep. PSW-GTR-149. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station: p. 49-56
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