Takano, L. L. , Unpublished Material, Mariana common moorhen - wetland summary data.
| Range of values | |
|---|---|
| Minimum: | 0 |
| Maximum: | 33 |
Concatenated UTM pair consisting of a leading N or E (northing or easting) and a 6 (E) or 7 (N) digit number representing meters.
List of wetland names or identifiers.
| Value | Definition |
|---|---|
| permanent | |
| seasonal |
This study was funded by the U.S. Navy
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The Mariana Common Moorhen is federally listed as an endangered species and among the recovery goals for this subspecies is to attain more information on moorhen movement pattern and home range during the dry and wet season. In addition, an updated moorhen estimate is needed.
Moorhen adults, juveniles, and chicks were surveyed on Guam, Saipan, Tinian, and Rota. We reviewed literature on past moorhen surveys and descriptions of wetlands in the Marianas to determine locations of wetlands throughout the archipelago. Survey efforts covered all permanent and seasonal wetlands on Saipan and Tinian during the dry and wet season. On Rota, wetlands were located on the golf course. On Guam, all permanent wetlands were surveyed where access was possible (approximately 90% of all wetlands on Guam) during the dry season. Depending on the size of the wetland, fifteen minutes to three hours was spent at each site.
Most surveys consisted of visual observations by two persons using binoculars during crepuscular hours when moorhens were most active. We also used audio playbacks in wetlands that were more enclosed and heavily vegetated. During these surveys, observers were stationed in different areas of the wetland and hidden from view within the vegetation. We found that staying hidden was crucial in order for moorhens to respond to audio playbacks. This audio survey method did not work on more open wetlands such as Fena Reservoir on Guam. During audio surveys, adult moorhen calls were played three to five times at approximately 30-second bursts. Playback calls have been used successfully by Brackney and Brookout (1982) to census the Common Moorhen (Gallinula chloropus). They found isolated moorhen pairs responded to the tape-recorded calls as readily as pairs in high density areas. Common Moorhens also responded equally well throughout the breeding season; however, males responded (93%) to tape calls a greater percentage of the time than females (21%). Therefore, we believe our survey method of using audio playbacks to enhance visual observations are unlikely to produce overestimations, but underestimations may occur. Moorhen calls and visual observations were recorded on a map and compared by each observer at the end of 15 minutes.
A complete census of all individuals was possible in many man-made wetlands, although it was difficult in natural wetlands. For example, on Saipan, a World War II abandoned concrete oil tank (approximately 0.5 ha), inundated by rainwater, was used by moorhens. In this tank, a complete view of all inhabitants could be seen from one vantage point through a spotting scope during daylight hours. Similarly, complete censuses were possible on small man-made drainage basins, golf-course ponds, and fish ponds, when the perimeter of the wetland was walked and moorhens flushed out of narrow bands of vegetation.
Multiple island-wide surveys on Saipan (N = 8) and Tinian (N = 7) took place from 16 May through 6 September 2001. On Guam, two island-wide surveys were conducted in May and June 2001. With the exception of Rota, each island-wide survey was carried out over a two-week period. On Rota, a survey was conducted on 13 August 2001 at a wastewater treatment system and wetlands on an 18-hole golf resort. Since creation of the golf course in 1994, its water treatment polishing ponds have attracted a variety of migratory birds, including one breeding pair of Mariana Common Moorhens (Worthington 1998).
When possible, moorhens were classified by age: adult, juvenile, and chick. Since subadults and adults were difficult to distinguish during surveys, we included subadults with the adult counts. The total count of moorhen adults, juveniles, and chicks for each two-week period was summed by age class across all wetlands visited to determine population estimates for each island and the subspecies.
Saipan and Tinian surveys encompassed both the dry and wet seasons. Therefore, I further examined whether there were any patterns to moorhen distribution and abundance among permanent, semipermanent, and seasonal wetlands on Saipan and at Lake Hagoi on Tinian.
Reference:
Takano, L. L. , Unpublished Material, Mariana common moorhen telemetry data - 2001.
Takano, L. L. , Unpublished Material, Mariana common moorhen home range data.
No tests for attribute accuracy were conducted
Refer to Methodology section
Not applicable
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