Field trials of line-transect surveys of bird carcasses in agro-ecosystems of Argentina’s Pampas region

Abstract

Abstract Pesticides caused high mortality of birds in agro-ecosystems of Argentina’s Pampas region during 1995–2003. As part of a program to monitor mortality events, we trained observers in distance sampling methods, conducted field trials under simulated conditions to assess the degree to which the critical assumptions of line-transect surveys were met, and estimated the density and number of chicken carcasses randomly placed along fixed transects in corn stubble, corn, alfalfa, wheat, pasture, and forest. The assumption of 100% detection probability of carcasses at 0 distance was met. We measured cluster size (1–5 carcasses) exactly and measured perpendicular distance from a cluster to transect centerline (0–40 m) with little error (absolute difference between actual and measured distances: x=0.14 m, SE=0.01, n= 121). Cluster detection was not size-biased in corn stubble but was size-biased in corn, alfalfa, wheat, pasture, forest, and all strata combined. Thirteen 3-observer teams performed equally w...