Abstract:
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.
