Modification of Point Counts for Surveying Cropland Birds

Abstract

As part of a comparative study of agricultural impacts on wildlife, modifications to the point count method were evaluated for surveying birds in, and adjacent to, cropland during the breeding season (May to early July) in Ontario. Location in the field, observation direction and distance, number of visits, and number of study sites per farm were examined using point counts of 5-minute duration in 1989 and 10-minute duration in 1990. Bird species number and abundance were not significantly different between point counts conducted from field-edge and field-interior (100 m or less from the edge) locations at the same study site (median field size = 6 ha). At each field-edge location, semicircular counts detected significantly fewer, but still about 85 percent of species and 80 percent of individuals detected in circular counts. We attributed the poor performance of circular counts to poor visibility through wooded field-edges, poor habitat quality, and an edge-effect on bird activity. Limited-distance (within 100 m of observer) point counts detected significantly fewer, and only 59 percent and 69 percent of species and individuals detected with unlimited-distance (but still on farm) point counts per study site in 1989 and 1990. Species number of each study site was still increasing significantly for all point count methods after three visits in 1989 and four visits in 1990. Bird abundance at each site was not significantly different among visits in 1989 or among the last three of four visits in 1990. We argue these results reflect spatial dynamics in the distribution of birds and species in cropland throughout the breeding season. Our study farms appeared to be well-sampled by field-edge, semicircular, unlimited-distance point counts at a sampling intensity of one study site per 26 ha based on comparisons with point counts from a larger number of study sites, search (walk-about) surveys of study sites, and noncrop areas on farms. Relevance of our results to recommended point count standards is discussed.

Parent Publication

• Monitoring bird populations by point counts

Citation

Freemark, Kathryn; Rogers, Catherine. 1995. Modification of Point Counts for Surveying Cropland Birds. 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. 69-74