Documenting changes in distribution is necessary for understanding species' response to environmental changes, but data on species distributions are heterogeneous in accuracy and resolution. Combining different data sources and methodological approaches can fill gaps in knowledge about the dynamic processes driving changes in species-rich, but data-poor regions. We combined recent bird survey data from the Neotropical Biodiversity Mapping Initiative (NeoMaps) with historical distribution records to estimate potential changes in the distribution of eight species of Amazon parrots in Venezuela. Using environmental covariates and presence-only data from museum collections and the literature, we first used maximum likelihood to fit a species distribution model (SDM) estimating a historical maximum probability of occurrence for each species. We then used recent, NeoMaps survey data to build single-season occupancy models (OM) with the same environmental covariates, as well as with time- and effort-dependent detectability, resulting in estimates of the current probability of occurrence. We finally calculated the disagreement between predictions as a matrix of probability of change in the state of occurrence. Our results suggested negative changes for the only restricted, threatened species, Amazona barbadensis, which has been independently confirmed with field studies. Two of the three remaining widespread species that were detected, Amazona amazonica, Amazona ochrocephala, also had a high probability of negative changes in northern Venezuela, but results were not conclusive for Amazona farinosa. The four remaining species were undetected in recent field surveys; three of these were most probably absent from the survey locations (Amazona autumnalis, Amazona mercenaria and Amazona festiva), while a fourth (Amazona dufresniana) requires more intensive targeted sampling to estimate its current status. Our approach is unique in taking full advantage of available, but limited data, and in detecting a high probability of change even for rare and patchily-distributed species. However, it is presently limited to species meeting the strong assumptions required for maximum-likelihood estimation with presence-only data, including very high detectability and representative sampling of its historical distribution.

The Neotropical Biodiversity Mapping Initiative (NeoMaps; http://neomapas.org/) proposes a strategy for surveying biodiversity in developing countries, and has been recently implemented in Venezuela. NeoMaps sampling universe is based on 170 cells in the Venezuelan Biodiversity Grid (VBG), with at least 30% terrestrial coverage accessible by road. We applied a stratified sampling design to select a set of 27 cells spanning environmental and biogeographical variation and implemented standardized field sampling protocols for birds, along 40 km long roadside transects of maximum environmental change within each cell (gradsects). Between March to April 2010 two surveys were performed on consecutive days along each transect: on the first day, three-minute point counts were performed at 50 stops, 800 m from each other. On the second day, cumulative species lists were recorded at a selection of 10 stops sampled for 9 min each. Total fieldwork time was ~243 person-days (3 days/gradsects x 27 gradsects x 3 persons). Bird surveys effort was ~729 person/hrs (mean = 4.5 hrs/day x 2 days/location x 27 gradsects x 3 persons). This dataset contains the detection histories (1: detected, 0: not detected) for eight species in the genus Amazona (Psittacidae): Amazona amazonica, Amazona ochrocephala, Amazona farinosa, Amazona barbadensis, Amazona dufresniana, Amazona festiva, Amazona mercenaria and Amazona autumnalis.

Supplement to: Ferrer-Paris, José R; Sánchez-Mercado, Ada; Rodríguez-Clark, Kathryn M; Rodríguez, Jon Paul; Rodríguez, Gustavo A (2013): Using limited data to detect changes in species distributions: Insights from Amazon parrots in Venezuela. Biological Conservation, 173, 133-143