Conservation of Neotropical Parrots: Population Responses to Forest Cover Change and Trade Pressure and a Tool to Predict Sensitivity to Deforestation

Abstract

The avian order Psittaciformes (parrots) is one the most at-risk group of birds in the world because of the combination of deforestation and overexploitation for wildlife trade. Studies to better understand and quantify the relative threats of deforestation and overexploitation are needed for conservation and management. The Central American country of Nicaragua provides an opportunistic study system towards that end. Deforestation and trade pressure have occurred consistently over multiple decades, including 1995 to 2013, a two-decade period from which population monitoring data is available. We used species-specific population data from a nation-wide parrot monitoring program to test the effects of deforestation and trade pressure and used a predictive tool to identify correlates to parrot sensitivity to deforestation.

To understand the effects of deforestation on parrot populations, we used Normalized Difference Vegetation Index (NDVI) to determine the extent deforestation affects population trends, described by occupancy. We ran multiple profile analyses to compare distribution-specific NDVI and species-specific occupancy. Population trends explained by NDVI demonstrated a regional pattern between the Pacific and Caribbean and showed two primary connections to forest cover change. While some parrots were negatively affected by forest loss and declined, others appeared to take advantage of the resulting open habitats.

Because of its smaller human population densities surrounded by more intact forest, we focused on the Caribbean region to better understand the dynamics of trade pressure on parrot populations. We evaluated the effect of geographic accessibility, a surrogate variable to estimate trade pressure from poacher activity, on parrot occupancy in the year 2013. We produced an accessibility metric adjusted for population density and used them as site covariates in occupancy models to explain occupancy. Geographic accessibility depressed parrot populations for some species, but not all. Accessibility was of greater relevance for species with apparent high market demand and less for species with apparent lower market demand.

Finally, as a tool to predict parrot sensitivity to deforestation and understand characteristics associated with high levels of sensitivity, we generated species-specific sensitivity to deforestation values, objectively represented by the coefficient of conservatism (CoC). The CoC is empirically generated by NDVI values and parrot presence or absence. Using Bayesian statistics, we tested the sensitivity values to determine their relationship to eight biogeographic, biological, and ecological variables. Results showed that parrots are predisposed to varied responses to deforestation related to the biogeographic regions of their distributions, adaptations to habitat types, and their dispersive nature. Additionally, the results implied that species with higher CoC values ought to be given careful conservation assessment to determine if they are at increased risk because of their sensitivity to deforestation.