The Yellow-Shouldered Amazon - Perspectives
There are 330 parrot species worldwide, of which a third is threatened with extinction. The Yellow-shouldered Amazon (Amazona Barbadensis) is a parrot species found in northern Venezuela and on the Caribbean islands Margarita, La Blanquilla and Bonaire. The total population size is estimated at 3.000-10.000 parrots, which has led the IUCN to classify its global condition as vulnerable. The population size on Bonaire is estimated at 800 parrots.
The goal of this study was to examine both the threats A. Barbadensis is facing on Bonaire and the opportunities to resolve them. Three methods were used during this process. First a literature study was conducted regarding the population dynamics of A. Barbadensis on Bonaire, resulting in a quantification of the different population parameters and environmental factors, affecting the parrot population. Secondly, a population dynamics simulation model was used to determine the sensitivity to changes in these environmental factors and population parameters. The model was finally used to analyze the impact of several scenarios on the population size over a period of 200 years.
The most important factor constraining the growth of the parrot population on Bonaire, is the limited number of nest sites in both trees and cliffs. Nest site limitation is inferred from the fact that only 21.5% of the population breeds annually. The low supply of tree cavities is caused by the exotic and invasive goats and donkeys who are responsible for the degraded state of the vegetation since their introduction in the 16th century. An eradication program would allow the ecosystem to restore to its natural balance. A. Barbadensis would benefit by increased survival in all life stages due to a substantial increase in food resources, which will prevent the parrots from having to visit the hazardous urban areas, and by an increase in the number of nest sites. The scenario exploring the effects of this drastic measure reveals a population growth to several thousands of parrots.
It must be noted however that this scenario does not include any density dependant factors that would eventually limit the growth rate.
The population is most sensitive to changes in juvenile and adult survival, which corresponds with the r/K selection theory and another theoretical viability study regarding A. Barbadensis. Conservation initiatives should therefore focus on increasing their survival as it will be more beneficial to the persistence of the species than improving upon chick survival and female reproductivity.
The exact effects of climatic stochasticity on parrots are not well known. This study assumed the climate affected both survival in all life stages as well as reproduction. Changes in the impact of the climatic stochasticity showed a high sensitivity, which emphasizes the need for a better understanding of the impact the climate has on the survival and reproductive parameters of A. Barbadensis. The parrot population on Bonaire can be considered as viable as the current conditions will not lead to extinction, nor will any of the other scenarios examined in this study. However, the reality might consist of a combination of these scenarios, affecting the parrot population more severely. It is therefore recommended, as a bare minimum conservational approach, to maintain the annual count of the population size in order to readily notice a decline in population size, enabling counter measures to be taken accordingly.