Graduate Thesis Or Dissertation
 

Seasonal movement, home range, and abundance of the Mariana Common Moorhen (Gallinula chloropus guami) on Guam and the northern Mariana Islands

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  • The endemic avifauna of Guam and the Mariana Islands represent a unique assemblage of bird species found nowhere else in the world and thus, are of considerable biological and conservation importance. Unfortunately, most of these species are understudied and exist in precariously low populations. The endangered Mariana Common Moorhen (Gallinula chloropus guami), one of the last remaining native waterbirds, is a prime example of this since information is lacking for development of an effective recovery plan. Thus, this thesis attempts to provide much needed information regarding moorhen space use, seasonal movement, distribution, and abundance. In Chapter 2, the dynamic use of space and movement among moorhens within and across landscapes on multiple islands is explored throughout the annual cycle. Adult Mariana Common Moorhens were radio-marked on Guam (N=25) and Saipan (N=18) to determine home range and inter- and intra-seasonal movement patterns in 2000 and 2001. Birds were tracked throughout the dry and wet season. During the dry season, 48 and 11.1% of radio-marked adults on Guam and Saipan, respectively, dispersed from their capture site to another wetland site. During the wet season, 71.4 and 70% of radio-marked birds on Guam and Saipan, respectively, dispersed from their capture site to another wetland site. In 2001, Saipan moorhen surveys indicated juveniles dispersed during the onset of the rainy season. Thus, intra-island movement increased during the wet season. Similarly, inter-island movement occurred from Saipan to Tinian during the onset of the wet season. On Guam, moorhens were more likely to move greater average distances in the wet season than the dry season. Among Guam moorhens captured on Fena Reservoir (N=9), Guam and that dispersed during the 2000 wet season, 66.6% returned to Fena Reservoir during the 2001 dry season. During the wet season, the frequency of movement among sites was inversely proportional to the average distance between each site. Home-range estimates on Guam averaged 3.1 ha ± 4.8 SD and did not differ significantly between sexes or seasons. However, during the dry season, females exhibited significantly smaller mean core areas than males. To our knowledge, this is the first radio telemetry study that has taken a multi-island approach to understanding a mobile islands species throughout its annual cycle. In Chapter 3, population estimates for the Mariana Common Moorhen were determined on Guam, Saipan, Tinian, and Rota from island-wide surveys conducted from May through September 2001. We estimate the total adult moorhen population to be 287, including 90, 154, 41, and 2 adult moorhens on Guam, Saipan, Tinian, and Rota, respectively. Surveys also revealed changing moorhen distribution throughout the annual cycle and suggested inter-island movement from Saipan to Tinian occurred during the onset of the wet season. Surveys conducted on Fena Reservoir from March through August 2000 indicated adult moorhen numbers were significantly less than those from a similar survey in 1988. In addition, nest surveys of six territories revealed 58.8 % egg loss and 71.4% chick loss. Conservation efforts for this subspecies have mainly focused on protection of remaining wetlands. Efforts need to be expanded to include more active monitoring of populations, vegetation management, and predator control on wetlands throughout the Marianas and Guam.
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