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«Collared Kingfisher. Photograph by Dan Clark Pacific Reef Heron. Photograph by Dan Clark Table of Contents Executive Summary Introduction Methods ...»

-- [ Page 1 ] --

STATUS OF THE LAND AND WETLAND AVIFAUNA OF

PAGAN, MARIANA ISLANDS

Ann P. Marshall and Fred A. Amidon

U.S. Fish and Wildlife Service, Pacific Islands Fish and Wildlife Office

300 Ala Moana Boulevard, Honolulu, Hawaii

December 2010

Collared Kingfisher. Photograph by Dan Clark

Pacific Reef Heron. Photograph by Dan Clark

Table of Contents

Executive Summary

Introduction

Methods

Results

Discussion

Acknowledgements

References

List of Figures Figure 1. Forest bird survey Transects on the island of Pagan………………………………………………………………… 5 Figure 2. Mariana common moorhen survey stations around the lower and upper lake…………………........ 7 Figure 3. Nightingale reed-warbler survey stations around the lower and upper lake…………………………….. 8 Figure 4. Forest bird density estimates…………………………………………………………………………………………………..11 Figure 5. Collared kingfisher density estimates on Pagan and other islands…………………………………………...13 Figure 6. Micronesian honeyeater density estimates on Pagan and other islands…………………………………..13 Figure 7. Micronesian starling density estimates on Pagan and other islands…………………………………………14 Figure 8. White-throated ground-dove density estimates on Pagan and other islands……………………………14 List of Tables Table 1. Birds detected on Pagan during forest bird surveys……………………………………………………………………10 Table 2. Detections per station by region of Pagan………………………………………………………………………………….11 Table 3. Detection probability (DP) for nightingale reed-warbler on Pagan……………………………………………..12

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Appendix 3. Pagan landcover mapping…………………………………………………………………………………….26 Executive Summary Avian surveys were conducted on the island of Pagan in June 2010 by the U.S. Fish and Wildlife Service to provide density and abundance estimates for the native forest birds. In addition, focused surveys were conducted to determine if the endangered Mariana common moorhen and nightingale reedwarbler were present on the island. Both species were thought to have been extirpated by the 1970s.

Sufficient detections of white terns, white-throated ground-doves, collared kingfishers, Micronesian starlings, and Micronesian honeyeaters were recorded to estimate densities. Based on available forested habitat, we estimate there are 2,920 (+ 916 SE) white terns, 602 (+ 173 SE) white-throated ground-doves, 725 (+ 127 SE) collared kingfishers, 11,158 (+ 2,768 SE) Micronesian starlings, and 5,468 (+ 1,964 SE) Micronesian honeyeaters on Pagan. Nightingale reed-warblers and Mariana common moorhens were not detected during surveys. Additional searches are needed to infer extirpation of the nightingale reed-warbler and Mariana common moorhen on Pagan. We recommend removing feral ungulates and restoring the wetlands and native forests on the island to promote long-term native bird conservation in the region.

3 Introduction Pagan is the largest of the islands of the Commonwealth of the Northern Mariana Islands (CNMI) north of Saipan (Ohba 1994). It is around 48 sq. km and consists of distinctive northern and southern sections connected by a narrow isthmus (Figure 1). The larger northern section of the island is dominated by an active volcano, Mt. Pagan, which was smoking throughout the survey period. Because of the last major eruption in 1981, there are large areas of lava fields with volcanic ash and little vegetation. The vegetation in the northern part of the island is predominantly ironwood (Casuarina equisetifolia) forest (Ohba 1994). There is a large flat area at the southern foot of Mt. Pagan still retains the runway built during World War II (Ohba 1994). The runway is still used for landing small planes and helicopters and for sling loading equipment, and the neighboring shoreline area is used for housing by temporary residents. The isthmus is dominated by swordgrass (Miscanthus floridulus), typical of areas where native forest has been degenerated by grazing pressure from feral goats (Capra hircus) (Ohba 1994).

The southern section of Pagan contains three old volcanoes and still includes large areas of native forest.

However, grazing pressure is having adverse impacts on the native vegetation here as well (Ohba 1994).

Chamorros (the indigenous people of the Mariana Islands) are believed to have developed long-term settlements on the northern islands around 1,000 years ago (Russell 1998). Radiocarbon analysis at a latte village site on Pagan indicated that the site was probably occupied by A.D. 1300 (Egami and Saito 1973). Pagan was inhabited in historical times but people were evacuated due to the 1981 eruption, and since then, the island been only sporadically inhabited for short periods of time.

There are two lakes located on the island, Lake Sanhiyong, an approximately 16-ha saltwater lake on the western shore (locally known as Lower Lake) and Lake Sanhalom, an 11-ha, somewhat brackish/freshwater lake farther north (called Upper Lake or Inner Lake) at the foot of Mt. Pagan (Figures 2 and 3). Two endangered species, which are now apparently extirpated from the island, once occurred on Pagan in association with these lakes: the Mariana common moorhen (Gallinula chloropus guami) and the nightingale reed-warbler (Acrocephalus luscinia yamashinae). The wetland habitat was drastically altered and reduced in the last century due to development by the Japanese, as well as the presence of feral goats, pigs (Sus scrofa) and cows (Bos taurus), and volcanic eruptions (Corwin et al.





1957, Marche 1889, Reichel et al. 1992, Tenorio and Associates 1979). The vegetation around the upper lake was virtually eliminated during the 1981 and subsequent eruptions and in 1992, Reichel et al.

(1992) estimated that there was less than a one percent vegetative ground cover bordering both lakes and no emergent vegetation in either.

The Mariana common moorhen was first recorded on Pagan in 1932 (Stinson et al. 1991). Both lakes apparently supported populations of the Mariana common moorhen, though it was less numerous at the Lower Lake (20+ compared to over 50 at the upper lake recorded in the 1960s) due to less emergent vegetation, higher salinity, and being subject to more human impacts (Corwin et al. 1957, Stinson et al.

1991). The last observation of a Mariana common moorhen on Pagan was one bird in 1979, subsequent trips to the island resulting in no sightings (Stinson et al. 1991, Tenorio and Associates 1979).

The Pagan subspecies of the nightingale reed-warbler is primarily known from specimens collected in 1887 and 1931 that indicate it may have been locally common in wetlands (Reichel et al. 1992).

Residents of the island indicate the species was present until at least the 1960s but occurred only in 4 Figure 1. Island of Pagan showing the location of forest bird survey transects sampled in 2010.

5 wetlands near the Upper, or possibly both, of the island’s lakes. Nightingale reed-warblers have not been observed on Pagan since the 1960s despite surveys made in the late 1970s, six trips (including intensive surveys in the vicinity of both lakes) made to the island between 1983 and 1989, and surveys in 1999 and 2000 (Division of Fish and Wildlife (DFW) 2000, Reichel et al. 1992, Tenorio and Associates 1979).

Native forest birds that occur on Pagan include the endangered Micronesian megapode (Megapodius laperouse laperouse), the Micronesian starling (Aplonis opaca), Micronesian honeyeater (Myzomela rubratra), collared kingfisher (Todiramphus chloris), and white-throated ground-dove (Gallicolumbra xanthonura) (DFW 2000). Early surveys primarily focused on the presence or absence of species from the island. However, in 1999 and 2000, the DFW conducted point-transect surveys on the island to estimate native bird populations. Unfortunately, due to poor weather they were only able to conduct surveys on the northern and southern half of the island in separate years (DFW 2000).

In June 2010, the U.S. Fish and Wildlife Service (USFWS) coordinated forest bird and wetland bird surveys on the island of Pagan as part of the “Marianas Expedition Wildlife Survey 2010” (MEWS 2010), funded through a contract with the Department of Defense -U.S. Marines through the Naval Facilities Engineering Command Pacific, Pearl Harbor, Hawaii. The local DFW and staff from the Northern Islands Mayor’s Office assisted with the project. The goals of these surveys were to estimate populations of native forest birds on the island by habitat type and determine whether Mariana common moorhen and nightingale reed-warblers were present on the island. Micronesian megapode surveys were also undertaken as part of this survey effort. The methods and results of the latter surveys are presented in a separate report.

Methods Point-Transect Surveys - To estimate forest bird population size we conducted island-wide point-transect surveys on Pagan from June 19 to 25, 2010. We sampled a total of 144 stations on 13 transects (Figure 1; there are no transects 12 or 13). All transects were placed in accessible forested areas across the island. We did not sample open field and coastal habitats because the object of the survey was to estimate forest bird populations. In addition, the narrow isthmus connecting the northern and southern sections of the island and the southern half of the south part of the island were not sampled due to the steep terrain and limited access. The starting point for each transect was determined by randomly selecting a points on a 150-m grid placed over the island using Geographic Information Systems (GIS). A transect composed of stations spaced 150 m apart was then established to maximize coverage of forested areas.

All surveys were conducted by one observer and followed standard point-transect methods, consisting of 8-minute counts and estimation of horizontal distances to all birds heard and/or seen (see Engbring et al. 1986 or Reynolds et al. 1980 for details). Rangefinders were used during the surveys to assist with distance estimation. The direction, based on compass reading, and time of detection were also recorded. Sampling conditions recorded included cloud cover, rain, wind, understory openness, habitat type, canopy height, and canopy cover. These parameters were later used as covariates in density calculations. Counts commenced at sunrise and continued until completed (typically prior to 1100 hours) and were conducted only under favorable weather conditions.

The point-transect technique requires 75-100 detections to model the detection function for each species effectively (Buckland et al. 2001). To achieve the minimum number of detections for collared 6 kingfishers and white-throated ground-doves we pooled all observations from the 1999 and 2000 DFW surveys, and included observations from a 2010 USFWS secondary counter (survey effort on stations counted twice was adjusted appropriately). Therefore, we used 434 collared kingfisher and 120 whitethroated ground-dove detections to model the detection function (Appendix 1). Densities were calculated using the program DISTANCE version 6.0 release 2 (Thomas et al. 2010) following procedures detailed in Camp et al. (2009a, b).

Lake Surveys- Surveys at the two lakes were conducted over 2 days, June 20 and June 21, 2010. On June 20, observers first established stations and conducted counts at Lower Lake. For Mariana common moorhen counts, three observers were stationed at 3 points along the west side of the lake (Stations 1, 2, 3; Figure 2). Counts were 30 minutes long and were divided into six 5-minute periods. During each 5minute period, observers scanned and listened for Mariana common moorhens. Any birds located during each 5-minute period were to be transcribed on a map of the lake as per procedures previously established for Mariana common moorhen counts (USFWS 1996). Also, a species list all birds seen or heard was recorded at each Mariana common moorhen station. Mariana common moorhen surveys began around 0630 hours (hrs) and ended around 0725 hrs for stations 1, 2, 3.

Figure 2. Island of Pagan showing the Mariana common moorhen survey stations around lower and upper lakes.

At Lower Lake, once the Station 1 observer was finished with his or her 30-minute Mariana common moorhen survey count, he or she began a playback survey for nightingale reed-warblers. Station 1 for the Mariana common moorhen was also station 1 for nightingale reed-warblers. Playback surveys consisted of digitally recorded nightingale reed-warblers from the Cornell Lab of Ornithology obtained 7 by Doug Pratt from Saipan. The call was played on an electronic game caller (Foxpro NX3™) for 30 seconds at each station. The observer listened for nightingale reed-warblers during the three minute survey period (30 seconds of playbacks and 2 minutes and 30 seconds of observation) and were to record the horizontal distances of any nightingale reed-warblers heard and/or seen. Rangefinders were to be used to assist with distance estimation and direction, based on compass bearing, and time of detection were to be recorded. All counts were conducted under favorable weather conditions. The observer then walked 150 m (using a GPS) for the next nightingale reed-warbler station (2), conducted the next playback and continued around the rest of the lake to the east side (picking up and dropping off (at Mariana common moorhen stations 4 and 5) the other 2 observers along the way) to finish at station 10 (station 6 for the Mariana common moorhen) (Figures 2 and 3). Nightingale reed-warbler counts started at 0705 hrs (station 1) and ended at 0819 hrs (station 10). The 3 observers began their 30minute counts for Mariana common moorhens on the west side (stations 4, 5, 6) between 0800 hrs and 0820 hrs and ended by 0850 hrs.

Figure 3. Island of Pagan showing the nightingale reed-warbler survey stations around lower and upper lakes.



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