VARIABILITY IN GRASSLAND BIRD COUNTS RELATED TO OBSERVER DIFFERENCES AND SPECIES DETECTION RATES

摘要: Abstract Differences among observers in ability to detect and identify birds has been long recognized as a potential source of error when surveying terrestrial birds. However, few published studies address that issue their methods or study design. We used distance sampling with line transects investigate differences detection probabilities three species grassland songbirds: Henslow's Sparrow (Ammodramus henslowii), Grasshopper (A. savannarum), Savannah (Passerculus sandwichensis). Our review 75 papers 1985–2001 found the most commonly were fixed-width (31%, 23 papers) fixed-radius point counts (20%, 15 papers). The median half-width strip by researchers was 50 m, but our results indicated 25 m for species. Beyond from transect line, we many 60% missed an...