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An age-structured population model of the Puerto Rican Parrot (Amazona vittata)

Authors:
  • CONACYT-Guyra Paraguay

Abstract

I wrote the computer simulation model PARPOP to investigate the population dynamic of the Puerto Rican Parrot (Amazona vittata), a species with < 50 individuals in the wild. The matrix model is age-class based and incorporates the effects of hurricanes on mortality and recruitment. Under the present intensive management, the probability of extinction for the population over a one hundred year period is 4.7%, with an average population of 206 birds after 100 years. Using actual fledging data for 1985-2000, the model adequately predicted the overall trends in the population but over-predicted population size through the 1990's. Population estimates, however, are presented without error values, making an evaluation of the accuracy of the model difficult. The modeled population was most sensitive to changes in mortality of older breeding individuals followed, closely by the proportion of females that attempt to nest. The model highlights the importance of maintaining, and increasing if possible, the intensive management of this species for its survival. Moreover, the modeling highlights the necessity for greater quantitative rigor in population estimation and in the estimates of survival for different age classes. To accomplish this, it is suggested that radio tagging be used since the techniques for capturing and radio-tagging parrots are well researched, have been successfully applied to the Puerto Rican Parrot and other species of Amazona, and the value of the data out-weigh the minimal risk associated with the technique.
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... Despite the potential importance of changes in annual survival to Puerto Rican Parrot population dynamics (Thompson 2004), there is little evidence that low levels of survival kept the parrot in a bottleneck except through the catastrophic impacts of hurricanes (Figs. 7 and 8). Elasticity analysis of a matrix population model for this species (Thompson 2004) similar to the one used in this paper (Appendix B) indicate that adult survival is the most sensitive (elastic) element. ...
... Despite the potential importance of changes in annual survival to Puerto Rican Parrot population dynamics (Thompson 2004), there is little evidence that low levels of survival kept the parrot in a bottleneck except through the catastrophic impacts of hurricanes (Figs. 7 and 8). Elasticity analysis of a matrix population model for this species (Thompson 2004) similar to the one used in this paper (Appendix B) indicate that adult survival is the most sensitive (elastic) element. Nevertheless, adult survivorship was relatively high during non-hurricane years (88%) from 1973 to 2000, although it may be lower in recent years (T. ...
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The relative importance of genetic, demographic, environmental, and cata- strophic processes that maintain population bottlenecks has received little consideration. We evaluate the role of these factors in maintaining the Puerto Rican Parrot (Amazona vittata )i n a prolonged bottleneck from 1973 through 2000 despite intensive conservation efforts. We first conduct a risk analysis, then examine evidence for the importance of specific processes maintaining the bottleneck using the multiple competing hypotheses approach, and finally integrate these results through a sensitivity analysis of a demographic model using life-stage simulation analysis (LSA) to determine the relative importance of genetic, demographic, environmental, and catastrophic processes on population growth. Annual population growth has been slow and variable (1.0 6 5.2 parrots per year, or an average k ¼ 1.05 6 0.19) from 16 parrots (1973) to a high of 40-42 birds (1997-1998). A risk analysis based on population prediction intervals (PPI) indicates great risk and large uncertainty, with a range of 22-83 birds in the 90% PPI only five years into the future. Four primary factors (reduced hatching success due to inbreeding, failure of adults to nest, nest failure due to nongenetic causes, and reduced survival of adults and juveniles) were responsible for maintaining the bottleneck. Egg- hatchability rates were low (70.6% per egg and 76.8% per pair), and hatchability increased after mate changes, suggesting inbreeding effects. Only an average of 34% of the population nested annually, which was well below the percentage of adults that should have reached an age of first breeding (41-56%). This chronic failure to nest appears to have been caused primarily by environmental and/or behavioral factors, and not by nest-site scarcity or a skewed sex ratio. Nest failure rates from nongenetic causes (i.e., predation, parasitism, and wet cavities) were low (29%) due to active management (protecting nests and fostering captive young into wild nests), diminishing the importance of nest failure as a limiting factor. Annual survival has been periodically reduced by catastrophes (hurricanes), which have greatly constrained population growth, but survival rates were high under non-catastrophic conditions. Although the importance of factors maintaining the Puerto Rican Parrot bottleneck varied throughout the 30-year period of study, we determined their long-term influence using LSA simulations to correlate variation in demographic rates with variation in population growth (k). The bottleneck appears to have been maintained primarily by periodic catastrophes (hurricanes) that reduced adult survival, and secondarily by environmental and/or behavioral factors that resulted in a failure of many adults to nest. The influence of inbreeding through reduced hatching success played a much less significant role, even when additional effects of inbreeding on the production and mortality of young were incorporated into the LSA. Management actions needed to speed recovery include (1) continued nest guarding to minimize the effects of nest failure due to nongenetic causes; (2) creating a second population at another location on the island—a process that was recently initiated—to reduce the chance that hurricane strikes will cause extinction; and (3) determining the causes of the low percentage of breeders in the population and ameliorating them, which would have a large impact on population growth.
... The newly establishing population at Rio Abajo is located around the site of the Rio Abajo aviary and it is thought that the presence of the captive birds has encouraged the released birds to establish their population nearby (White et al. 2012). Forty individuals were released at El Yunque between and 2004, eight in 2008and six birds in 2010(Vélez-Valentín 2011. In 2013 plans were made to establish a third population on the island in the Maricao State Forest (western Puerto Rico) . ...
... Maintain the integrated conservation management programme. Improve synchronisation of breeding of wild and captive birds to increase the number of captive-bred chicks that can be fostered by wild parents (Thompson 2004). Integrate exotic mammalian predator trapping (black rats, small Indian mongooses, feral cats) into the existing conservation management programme, and monitor predator populations to study the efficacy of these measures (R. M. Engeman in litt. ...
... Maintain the integrated conservation management programme. Improve synchronisation of breeding of wild and captive birds to increase the number of captive-bred chicks that can be fostered by wild parents (Thompson 2004). Integrate exotic mammalian predator trapping (black rats, small Indian mongooses, feral cats) into the existing conservation management programme, and monitor predator populations to study the efficacy of these measures (R. M. Engeman in litt. ...
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Once numbering only 13 birds in the wild, this parrot has been saved from extinction. Conservation action has increased the population since 1975, but it remains Critically Endangered because the number of mature individuals remains tiny. If more released birds successfully breed in the wild and numbers remain stable or increasing, the species may warrant downlisting in the future.
... Although several factors are believed to contribute to the maintenance of the parrot's population bottleneck in the LEF, only recently has the relative importance of these factors been quantitatively assessed. For example, an age-structured population model indicated that the estimated parrot population of 48 birds in 2000 had a 4.7% chance of extinction in 100 years under present management (Thompson Baranello, 2000;Thompson, 2004). Sensitivity analyses of Thompson's model indicated that the modeled population was most sensitive to mortality of breeding-aged parrots followed by fledging success. ...
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a b s t r a c t The Luquillo Experimental Forest (LEF) located on the Caribbean island of Puerto Rico has a rich history of ecological research, including a variety of avian studies, and is one of the most active ecological research sites in the Neotropics. The LEF spans an elevational range from 100 to 1075 m over which five life zones and four forest types are found in a warm, humid subtropical climate. A total of 23 bird species breeds here and another 76 species, mostly migrants, are known to occur. The food web of the forest in the lower elevations is especially well studied, which allows an assessment of the role of birds in the food web. The LEF is noted for its high densities of Eleutherodactylus frogs and Anolis lizards, which may depress insect densities thereby contributing to the low species richness and densities of most insectivorous birds. The signature species of the forest is the endangered Puerto Rican Parrot (Amazona vittata) that has been the focus of intensive long-term research and recovery efforts, which have spawned research on associated species, including long-term studies on the Pearly-eyed Thrasher (Margarops fuscatus) and botfly (Philornis spp.) ectoparasitism. Given the frequency of hurricane disturbance to the LEF and studies providing baseline for comparisons, research has made major contributions to an understanding of the effects of hurricanes on forest ecosystems including bird populations and their resources. We summarize these and other studies from the LEF to characterize the avifauna and its environment while noting studies with management implications and identify opportunities for future ornithological studies. Published by Elsevier B.V.
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This publication summarizes the histories of all known Puerto Rican parrot nests in the Caribbean National Forest/Luquillo Experimental Forest from 1973 through 2000. Included for each nest, when known, are the identities of the pair, clutch size, known fertile and infertile eggs, number of eggs that hatched, number of chicks that survived, sources of mortality, fostering (source, destination, or both), number of young fledged from the pair and from the nest, and percentage of days the nest was guarded. This information is useful for detecting and assessing potential changes in reproductive output and nest threats and is fundamental for understanding some of the demographic and genetic factors influencing the wild parrot population.
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I contrast 2 views of modeling: the model as a representation of 'truth' and the model as a problem-solving tool. Examples are given of how, in the latter case, the objective drives the design of small, simple models that focus relentlessly on the problem to be solved. A number of applications for small, focused models are offered. I stress the need for wildlife professionals to develop the skills for constructing and using such models on a regular basis; I end with ideas about how to create a modeling culture in conservation and resource management organizations.
Improved capture techniques for psittacines
  • J M Meyers
Meyers, J. M. 1994. Improved capture techniques for psittacines. Wildl. Soc. Bull. 22: 511-516.