No abstract

BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses.

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: x̄=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 well in field trials regardless of having or not having observers with previous experience conducting transect surveys of bird carcasses in agro‐ecosystems. Teams with experienced and inexperienced observers missed clusters near the centerline (defined here as 1.5–5 m for wheat and 5–15 m for other strata) but detected all clusters on the centerline (defined here as 0–1.5 m for wheat and 0–5 m for other strata). Percent relative bias was 0.36% for corn stubble (n=39); 5.63% for the combined data of corn, alfalfa, wheat, pasture, and forest (n=73); and 0.51% for all strata (n=121). Bias estimates were small in relation to standard errors of density estimates, and the density estimator produced 95% confidence intervals that always included true densities. Predators and scavengers started removing carcasses during the first day of exposure (cumulative survival: x̄=0.69, SE=0.04, n=36) and stopped removing them after day 5 (cumulative survival: x̄=0.04, SE=0.02, n=5). Carcass removal rate averaged −0.38/day (SE=0.03). Although line‐transect sampling represents a viable method to estimate the density and number of dead birds in agro‐ecosystems, scavenging data should be collected to adjust these estimates, even when surveys are conducted the day following pesticide application. An effective communication network between collaborators and the general public and observer readiness are needed as part of research and monitoring efforts to guide decision‐making on agricultural practices, promote law enforcement, and manage wildlife in agro‐ecosystems.

No abstract

No abstract

Once abundant and widely distributed, the Bahama parrot (Amazona leucocephala bahamensis) currently inhabits only the Great Abaco and Great Inagua Islands of the Bahamas. In January 2003 and May 2002–2004, we conducted point‐transect surveys (a type of distance sampling) to estimate density and population size and make recommendations for monitoring trends. Density ranged from 0.061 (SE = 0.013) to 0.085 (SE = 0.018) parrots/ha and population size ranged from 1,600 (SE = 354) to 2,386 (SE = 508) parrots when extrapolated to the 26,154 ha and 28,162 ha covered by surveys on Abaco in May 2002 and 2003, respectively. Density was 0.183 (SE = 0.049) and 0.153 (SE = 0.042) parrots/ha and population size was 5,344 (SE = 1,431) and 4,450 (SE = 1,435) parrots when extrapolated to the 29,174 ha covered by surveys on Inagua in May 2003 and 2004, respectively. Because parrot distribution was clumped, we would need to survey 213–882 points on Abaco and 258‐1,659 points on Inagua to obtain a CV of 10–20% for estimated density. Cluster size and its variability and clumping increased in wintertime, making surveys imprecise and cost‐ineffective. Surveys were reasonably precise and cost‐effective in springtime, and we recommend conducting them when parrots are pairing and selecting nesting sites. Survey data should be collected yearly as part of an integrated monitoring strategy to estimate density and other key demographic parameters and improve our understanding of the ecological dynamics of these geographically isolated parrot populations at risk of extinction.

The green iguana (Iguana iguana) was most likely introduced as a pet and became overabundant during the last 20 years on Grand Cayman. Because negative impacts were unmanageable (e.g., damage to buildings and other infrastructure), a harvest management strategy was developed and implemented, and over 874,252 green iguanas were

I conducted transect surveys of pigeon and dove (Columbidae) nests on Puerto Rico, Vieques, and Culebra islands. Nest detection probability and density differed between study areas in January–August 1991 and 1992. Nest detection probability and density did not differ between years or among species, so I used transect data from a larger study (1986–1999) to assess the relationships between nest density and rainfall, food abundance, food diversity, and predator abundance along transects. Food abundance was the most important predictor of annual changes in nest density on the surveyed transects in mesic and xeric habitats during May–June 1986–1999. Positive correlations of annual nest density estimates suggested parallel responses among columbid species to similar or covarying resources in mesic and xeric habitats.