Making inferences about non-detection observations to improve occurrence predictions in Venezuelan Psittacidae

Abstract

The global decline in psittacid populations highlights the need for monitoring programmes that allow us to estimate the level of confidence that can be placed in a non-detection observation in order to assess changes in range status. We used the detection/non-detection records for 26 psittacid species detected during the first national bird monitoring programme in Venezuela carried out in 2010 by the Neotropical Biodiversity Mapping Initiative. We fitted occupancy models and evaluate the suitability of the data to explain the lack of detections given the current sampling effort, and the expected occurrence probabilities due to environmental conditions (conditional probability of occurrence; ΨCONDL). We were able to fit reliable models for 13 of the 26 species detected. For Green-rumped Parrotlet Forpus passerinus, Blue-headed Parrot Pionus menstrus, and Orange-winged Amazon Amazona amazonica, the probability of detection (p) under the current sampling effort was too low (> 0.2) in areas where environmental conditions would imply high ΨCONDL ( 0.2), suggesting that the species are reliably detected and better models could be obtained by including other predictive variables related to temporal use of resources and habitat heterogeneity. To improve the effectiveness of parrot monitoring programme in Neotropical countries, we suggest increasing the sampling effort, developing several surveys per year, and including variables related with temporal use of resources and habitat heterogeneity