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    Author(s): J. Edwards Gates
    Date: 1995
    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. 135-144
    Publication Series: General Technical Report (GTR)
    Station: Pacific Southwest Research Station
    PDF: View PDF  (1.6 MB)

    Description

    The effects of point count duration and radius on detection of breeding birds were compared by recording all birds seen or heard within two consecutive 5-minute intervals and for fixed-radius (within 30 m) or unlimited radius counts. Counts were conducted on Green Ridge State Forest (GRSF) and Savage River State Forest (SRSF) in western Maryland. More than 70 percent of all detections during fixed- and unlimited-radius counts occurred within the first 5 minutes. There was little overall gain in species richness from counting an additional 5 minutes. With fixed-radius counts, eight species at GRSF and two at SRSF showed significant differences in detections between the first and second 5 minutes. Using unlimited-radius counts, the resultant larger sample had a higher number of bird species showing significant differences between the first and second 5 minutes, 23 at GRSF and 12 at SRSF. Still, minimal changes in overall rank of species abundance resulted from counting an additional 5 minutes. About 80 percent of all bird detections and several new species were recorded >30 m from the counting point. Twenty-seven species at each of the two State Forests had significantly different detections within the two distance intervals. Compared with fixed-radius counts, detections >30-m distance often brought the rank order of species abundance up or down depending on whether the species had proportionally higher detections in the first or second distance interval. A time-distance interaction occurred with unlimited-radius counts, with more bird species >30-m distance tallied more often in the second 5-minute interval, indicating a possible increase in detection error with increasing distance and time. Observers may be recording more audible, nearby individuals first and only later noting less audible, more distant individuals. Fixed-radius counts done for 5 minutes should provide reasonable indices to species richness and abundance in a particular habitat, whereas unlimited-radius counts would provide a more complete list of species present in a local region.

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    Citation

    Gates, J. Edwards 1995. Point Counts Modifications and Breeding Bird Abundances in Central Appalachian Forests. 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. 135-144

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