The Demography and Conservation of the Bahama Parrot on Great Abaco Island, Bahamas

Abstract

The status of the Bahama Parrot throughout the Bahamas Archipelago has been of concern since 1976, when the species was listed as endangered. To recover the species, two recommendations were put forth in the 1980s. First, to minimize the impact of mammalian predation on the Abaco population, secondly, reintroduce the species to historical portions of its range. Lack of sound biological information has precluded determining the status of the populations and potential of either parrot population to serve as a source for a translocation program. The goal of this study was to ascertain the current status of the population in Abaco and assess its viability. To meet this goal, I estimated population size and juvenile survival rates. I augmented information regarding reproductive ecology of the population by estimating nest density, nest success using the Mayfield method, estimating effects of mammalian predation upon nest survival and breeding adult survival rates. I used these data to determine if nest survival differed as a function of nest density, habitat condition (e.g., burned-unburned), and location (e.g., in or outside the Park). I used period survival of adults to assess the costs of reproduction on adult breeder survival rates. I also collected data on food availability and distribution of parrots to qualitatively assess seasonal habitat use and food availability. Finally, I used program VORTEX to determine the status of the species and address the following questions: 1) what is the viability of the Abaco population?; 2) by how much do predators and hurricanes undermine the persistence of the Abaco population?; 3) to which parameters is the Abaco population most sensitive to, and 4) what is the combination of lowest values for selected vital parameters that would lead to a persistent population?.

Population numbers of the Bahama Parrot estimated in May 2002 to 2004 ranged from 1578 to 2600. In 2005, only 1/3 of parrot detections were made as compared to previous years. I believe passage of hurricanes Frances and Jeanne in September 2004 contributed to this drop. Breeding productivity in 2003 was 1.23 fledglings per nest attempt. In 2004, breeding productivity was 0.8. Nest success was 0.5. Daily survival probability did not differ between high density areas (0.025 nests/ha) when compared to nests in lower density areas (0.008 nests/ha). On 10 July 2004 a lightning ignited fire burned over 1,850 m2 of the study area. None of the nests in the path of the fire were lost to its immediate impact. Nest success of these nests did not differ significantly from unburned nests 0.47 vs 0.51 respectively. The total estimated number of nests in the study area was 289 (SE = 85). In 2004, 578 (95% CI = 238-918) birds were breeding, or 22% of the estimated population. Survival of breeding adults during the nesting cycle was estimated to be 0.87 for females and 0.92 for males. Thirty-one nestlings where instrumented in 2003, of which 3 died after climbing out of the nest. The estimated first-year survival probability for the remaining 28 juveniles was 0.76 (95% CI = 0.53 - 0.99).

Birds concentrated in two areas to the north and southwest—Crossing Rock and Sandy Point. Distribution patterns corresponded closely with patterns of food availability. Food availability was lowest during the winter, the period with the highest mortality of juveniles.

Population simulations yielded a persistence probability for the Abaco population of 0.997 over 100 years. However, the stochastic-r was -0.012, resulting in a decline of population size over this period. The only scenarios that yielded a positive stochastic-r was one with no predation by introduced mammals, or one with a breeding productivity of 1.4 chicks/nest attempt.

I view the Abaco population vulnerable to extinction. An 'endangered' designation is not justified at this moment because both populations enjoy relatively large population sizes, and with the exception of mammalian predation, no imminent threats to their continued existence. In order to prevent an 'endangered' designation, my results strongly suggest that Abaco non-breeding habitat be protected and that an effective predator control program needs to be implemented. Translocations continue to be central to the conservation of the species. Currently, the Inagua population is the preferred source of birds for translocations due to its tree-nesting habit, which offers a mechanism to deal with threats of mammalian predation at reintroduction sites. Translocations should be supported by sound demographic data and a genetic assessment that would identify ways to maintain maximum genetic diversity of the species and its multiple populations.