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Conservation and Population Ecology of The Bahama Amazon Parrot Amazona leucocephala bahamensis
If you were to travel the world from country to country, the flora and fauna that inhabited each place of visit would change dramatically. The level of speciation that has occurred across the world has given us millions of different types of organisms that have evolved adaptive qualities that make themselves most fit for survival in the area they inhabit. Each habitat differs in organic composition, nutrient levels, food sources, altitudes, and geological landscape. These factors can all change even over a relatively short distance, which explains why the world exhibits such a diversity of species (Nosil and Sandoval 2008).
Unfortunately, not all of these species are thriving in the way they should be. Many organisms are struggling to stay in existence. Changes in climate and habitat, ecological niche competition, as well as human interference can be put to blame for these endangered species. Without human aid in these situations, many unique species will vanish from Earth forever. One such example of an endangered species is the Bahama Parrot, a subspecies of the Cuban Amazon Parrot. This species once inhabited the islands of Abaco, New Providence, San Salvador, Long Island, Crooked Island, Acklins and Great Inagua. Today it only inhabits the islands of Abaco, the northernmost island, and Inagua, the southernmost island, of the Bahamas.
The Bahama Parrot (also referred to as the Bahama Amazon) has a morphology that one would expect from a tropical species. Their body is covered in bright green feathers, while their head contrasts with a bright pink throat and sold white crown. They hide vibrant blue flight feathers while perching in trees, but expose them on takeoff, making them very hard to miss while on the move (Gnam 1991). It is their aesthetically pleasing color combination that makes them targets for poaching or capture for domestication. Such a capture results in a $1,000 fine from the Government of the Bahamas under the Bahamian Wild Bird Protection Act (Gnam and Burchsted 1991). Their feet have two toes facing forward and two toes facing backward, a configuration known as zygodactylism that is common in arboreal species such as parrots, woodpeckers, and owls (Lockley et al 2007).
Simply looking at the morphology of the Bahama Parrot, even an ornithologist would have trouble distinguishing between birds from the Abaco population and from the Inagua population. The phenotypes of the different populations are identical. Where they differ is in their nesting behaviors, which has a very large impact on their reproductive success. Inagua Bahama Parrots (or Inagua Parrots) place roosts high in tree cavities, similar to many species of avia. The Abaco Bahama Parrot (or Abaco Parrot) is very unique in that it is the only New World Parrot that nests in subterranean limestone cavities (Stahala 2008). This subjects Abaco Parrots to nest predation by feral cats, flooding, and other ground predators (Gnam 1991). Both populations of Bahama Parrot feed on a variety of fruits, such as wild guava, poisonwood berries, pigeon berries, and fruit from the gumbo-limbo palm. During breeding season, Abaco Parrots feed on unripe pine nuts from Bahama Pines, which determine their breeding ground location. These pine nuts are vital for their increased need of nutrients for breeding (Snyder, King, and Kepler 1981). Bahama Parrots are monogamous for life, choosing one female as their mate for the remainder of their days.
Many of the qualities of the Abaco Parrot have made it a well-studied species in dealing with endangerment. The Bahama Parrot was placed on the Endangered Species Registry in 1976 (Stahala 2005). The most accepted hypothesis for their decline states that their drop in numbers had been due to poaching, capture for domestication, unprotected habitat, and nest predation due to subterranean nesting. The population was surveyed in 1976 and estimated at about 450-650 individuals on Abaco Island (Gnam and Burchsted 1991).
Many attempts have been made to aid this uncommon species in survival, some met with measurable success. Since efforts began in 1976, the Abaco ParrotŐs numbers have shown an upward trend, with 830-1080 individuals estimated living in 1989 (Gnam and Burchsted). An attempt at captive breeding and release, however, was met with failure, which left only a few options. Trapping of feral cats has aided in the reduction of nest predation on the island of Abaco, and with effort put forth by the people of the Bahamas, the first major national park in 20 years, Abaco National Park, was created in 1994. The park, located on the southernmost tip of the island, contains the majority of the Bahama Pines that are the only breeding grounds for the Abaco Parrot. Most recent population estimates from 2004 put the Abaco Parrot population at almost 4,000, almost ten times the numbers they had in 1976.
Many consequences arise from being an isolated small population. The divide between the two Bahama Parrot populations reduces gene flow, new genes transported to a population where they do not currently exist, which results in less diversity in both of the groups (Freeman and Herron 2007). Such events could lead to allopatric speciation, the evolution of traits that results in two different species when two areas of a population are genetically isolated from each other (Nosil and Sandoval 2008). With smaller isolated populations also comes the greater chance of an inbreeding depression, the reduced fitness of a population as a result of breeding between related individuals (Freeman and Herron 2007).
Small isolated populations face many ecological and evolutionary downfalls. When gene flow is reduced or nonexistent, no new genes enter a population, which reduces the chance of new adaptive genes to aid in a speciesŐ survival of an ever-changing habitat. Effects such as genetic drift begin to have a large effect when a population drops to dangerously low values. Genetic drift is the random changes in frequencies of alleles in a population (Freeman and Herron 2007). For every locus of a gene, two alleles exist. When working with a small population, the chance that an allele will increase or decrease in frequency is great, eventually leading to the domination of one allele and the extinction of the other allele at a locus (Taylor 2008). It is this danger that leads to a decline in heterozygosity in a population, which can protect an individual from deleterious alleles or genetic diseases. An equation exists that measures heterozygosity decline: Hg + 1 = Hg [1-(1/2N)], with N = population size. The smaller the population, the greater the rate of heterozygosity decline (Nagylaki 1983). This decrease in heterozygosity results in less fit individuals in the population, and makes the parrots more susceptible to extinction as a result of slight changes in the environment. At this point in the progression of a population, increasing habitat that was once destroyed will not aid in the success of the species. Only increasing genetic diversity by bringing in new individuals from the same species can increase the genetic diversity and save the species that is in danger of extinction. Unfortunately in many extreme cases, this situation occurs to the only population remaining of the species, which leaves the species in a serious scenario, termed bottlenecking. In this situation, so few individuals remain in a population that all remaining individuals of a population are in some way related to each other (Dunn and Byers 2008). It is at this step in the progression of the species that it is only a matter of time, even with the help of humans, before they become too unfit to live on their own, and face the option of extinction.
As the Bahama Parrot faces these dire consequences, it is the duty of humans to aid in keeping this grim future from occurring. Once a species reaches a certain point in this dark road to extinction, it seems very difficult to reverse the trend. Thanks to the hard work and effort put forth by many around the world and in the Bahamas, the extraordinary Bahama Parrot has been given a chance to fight the odds against it. Children one hundred years from now may get a chance to see one of the first birds viewed by Christopher Columbus when he discovered the New World (Gnam 1991). Studies following the fall and rise of the Abaco Bahama Parrot population can now be applied to other species walking the thin line of extinction and survival. Increasing the effort put into the fight to save the Bahama Parrot and other endangered species can ensure future generations full of unique, extraordinary organisms such as the Bahama Amazon Parrot.
Works Cited:
Dunn SJ, Byers JA. 2008. Determinants of survival and fecundity through a population bottleneck in Pronghorn (Antilocapra americana). Journal of Mammalogy 89(5): 1124-1129.
Freeman S, Herron JC. 2007. Evolutionary Analysis. Pearson Publishing Co. 4th Edition: 470-485.
Gnam R, Burchsted A. 1991. Population estimates for the Bahama Parrot on Abaco Island Bahamas West Indes. Journal of Field Ornithology 62(1): 139-146.
Lockley MG, Li R, Harris JD, Matsukawa M, Liu M. 2007. Earliest zygodactyls bird feet: evidence from Early Cretaceous roadrunner-like tracks. Naturwissenschaften 94(8): 657-665.
Nagylaki T. 1983. Evolution of a large population under gene conversion. Proceedings of the National Academy of Sciences of the United States of America 80(19): 5941-5945.
Nosil P, Sandoval CP. 2008. Ecological Niche Dimensionality and the Evolutionary Diversification of Stick Insects. PLoS One 3(4): e1907
Rivera-Milan FF, Collazo JA, Stahala C, Moore WJ, Davis A, Herring G, Steinkamp M, Pagliaro R, Thompson JL, Bracey W. 2005. Estimation of density and population size and recommendations for monitoring trends of Bahama parrots on Great Abaco and Great Inagua. Wildlife Society Bulletin 33(3): 823-834.
Snyder NFR, King WB, Kepler CB. 1981. Biology and Conservation of the Bahama Parrot Amazona leucocephala bahamensis. Living Bird 19: 91-114.
Stahala C. 2005. The Demography and Conservation of the Bahama Parrot on Great Abaco Island, Bahamas. North Carolina State University
Stahala C. 2008. Seasonal movements of the Bahama Parrot (Amazona leucocephala bahamensis) between pine and hardwood forests: Implications for habitat conservation. Ornitologia Neotropical 19(Suppl. S): 165-171.
Taylor JE. 2008. Environmental variation, fluctuating selection and genetic drift in subdivided populations. Theoretical Population Biology 74(3): 233-250.
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