2000 Technical Report #3 Wildlife and Vegetation Surveys GUGUAN 2000 Conducted By CNMI Division of Fish and Wildlife Wildlife Section With Assistance From The Northern Island Mayor's Office 4-10 JUNE 2000 Please cite as: Cruz, J. L. Arriola, N. Johnson, and G. Beauprez. 2000. Wildlife and Vegetation Surveys Guguan 2000. Technical Report #3 CNMI-DFW, unpubl. SUMMARY OF WILDLIFE SURVEYS GUGUAN ISLAND 4-10 JUNE 2000 Conducted by: CNMI Division of Fish and Wildlife Wildlife and Enforcement Sections P.O. Box 10007 Lower Base, Saipan 96950 and Northern Islands Mayor's Office P.O. 502859 Garapan, Saipan 96950 2 Executive Summary This trip was a combined effort of the Brown Tree Snake, Enforcement, and Wildlife programs of the Division of Fish and Wildlife and the staff from the Northern Islands Mayor's Office. The objectives were to assess the status of populations of seabirds, forest birds, bats, lizards, plants, and small mammals on Guguan. We focused particularly on populations of endangered species, especially on the endangered Micronesian megapode. Micronesian starlings were the most abundant forest bird detected. Micronesian honeyeaters were also quite common, and the endangered Micronesian megapode was more abundant on Guguan than on any other northern island. Forest birds appeared to be using open habitats extensively-perhaps because of the lack of Monitor lizards, feral animals, or large predators--therefore, bird populations are quite large despite the limited extent of forest on the island. Seabird colonies were surveyed and population sizes estimated. Populations of most species of seabird, including Brown and Black noddies, Brown and Red­ footed boobies, White and Red-tailed tropicbirds appear to be quite stable on Guguan. However, Sooty terns were significantly less abundant this year than during previous counts performed at the same time of year. In 2000, there appear to have been fewer active Sooty tern colonies than during previous surveys. Guguan is distinguished from the other islands surveyed with it's relatively high abundance and density of native tree species. The understory and smaller size classes on Guguan are expected, with a large number of individuals. It is clear that this ecosystem is much healthier than the other islands even thought it is recovering from the devastation of volcanic activity. Guguan could be one of the last refuges for native wildlife in the Marianas. It is imperative to keep feral animals away from Guguan as it has sensitive young forests. Introduction Guguan is unique in that it supports relatively large numbers of a variety of wildlife species including large colonies of seabirds, land birds, fruit bats, and coconut crabs. The island is constitutionally designated as a wildlife sanctuary and is managed by the Division of Fish and Wildlife. It is uninhabited, and has no feral ungulates. Habitats on the island are diverse. In the northern, central, and western parts of the island the terrain and vegetation are dominated by relatively recent volcanic activity. Large cinder fields, cinder cones, and lava flows are predominant. This is the most geologically active end of the island and appears to have undergone 3 many changes over the last 100 years. Visitors in 1876 described a rift in the western rim of a high (2000 foot) caldera that was large enough for boats to enter a brackish water lagoon (Cortes in Ludwig 1978). In the early 1900's, visitors described craters on the western side that had partially slipped into the sea (Fritz in Ludwig 1978). There are no lagoons or evidence of such craters currently, and we did not encounter any active steam vents or sulfur deposits. The large volcanic cone and surrounding cinder fields were in the process of being vegetated by grasses, vines and trees. The lava field in the picture is composed of barren lava as well as areas largely grassed over with islands of shrubs and small trees. The recent lava flow on Guguan with initial vegetation growth, June 2000. 4 Area of Sooty Tern colony with grasses and relatively new shrub growth, Guguan June 2000 The southern portion of the island is bounded by high cliffs, and is heavily vegetated. Rugged hills and valleys are densely forested with Pandanus sp., Terminalia, Hibiscus ti/iaceus, and other native forest trees. The southern plateau is dominated by sword grass, and a valley that runs diagonally across the center of the island separates the northern and southern sections. There were 4 coconut palms that survived from attempted plantings dotting this valley. Heavily vegetated sections of Guguan in the South, Guguan June 2000 Relatively few surveys of the island's wildlife have been conducted over the last 25 years: the island was circled on 15-16 July 1978 by fisheries biologists and volcanologists, but they were unable to land due to heavy seas and so estimated numbers of birds on the wing (Ludwig 1978). Four days were spent on the island in 1979 (Clapp and Hatch 1986) and again in 1983 (Lemke 1984). One day in March was spent off-shore during the Townsend Cromwell Raioma surveys of 1984, and seabird surveys were conducted for a short period oftime in May 1992 (Rice 1993). More thorough surveys of seabirds were conducted by Phil Glass and Stan Villagomez from 8 to 20 September 1986 (Glass 1986; Glass and Villagomez 1986), and again by Phil Glass and David Aldan from 28 May to 4 June in 1987 (Glass and Aldan 1987). During the more extended stays on Guguan, researchers focused their attentions on the nesting and foraging behavior of Micronesian megapodes and Mariana fruit bats. Other forest birds were observed but apparently have not been systematically surveyed prior to the present trip. Small mammals and reptiles were also observed during prior visits, but this is the first survey to systematically document their species and numbers. For this survey, Alvin Fitial (Enforcement), Tina de Cruz and Nathan Johnson (Wildlife) conducted bird, bat, and vegetation surveys. Richard Lazaro (BTS) and Larry Stoll (Northern Islands) conducted small mammal, and lizard surveys. Transportation to Guguan was provided by the Marlin II. Departure from Saipan was on June 4 and arrival on Guguan was on June 5 in the evening. On June 6­ 9 forest bird surveys, seabird surveys, skink and gecko surveys, rat trapping, and bat countsboth at the roost and on the foraging grounds were conducted. On June 10, Americopters provided transportation of gear and personnel to Alamagan. Forest Bird Surveys Forest birds were surveyed using Variable Circular Plot (VCP) methodology on 6 and 7 June 2000. The surveys were conducted from 6:00 to 10:30 a.m. by teams of one or two people. One person from each team counted birds both visually and by song for 5 minutes at each station, estimating the distance to each detection. Most birds were counted by their song or call notes, but in the open areas, they could easily be counted by sight as well. Point counts were performed at stations spaced every 150 m along four transects. The transects were set systematically to sample different habitats and were composed of between 5 and 12 count stations for a total of 36 stations (Figure 1). U.S. DEPARTMENT OF AGRICULTURE SOIL CONSERVATION SERVICE ! GUGUAN ISLAND NORTHERN MARIANA ISLANDS I 17" 18'54"N X 145°50'52"E a '/] ! I APPROXIMA TE SCALE - MILES a I U.~.PEFENSE SOURCE: MAPPING AGENCY AND SCS APPROXIMATE SCALE - KILOMETERS FIELD PERSONNEL; PROJECTION UNKNOWN ELEVATIONS ARE IN METERS. -- SCALE 1: 15.000 ./UNE 19/11) RASE 4-11-39792 Forest Bird VCP Transect 1, Guguan June 2000 Transect 1 ran through an area of grasses, vines and scattered trees colonizing a vast cinder field. This transect terminated on the open lava flow. Transect 2 began in an open cinder field, moved into a savanna, and then into a mixed native forest. Transect 3 began in mixed field and forest and ended in dense native forest. Transect 4 ran through savanna. Point count stations were not permanently marked but can be relocated using the GPS coordinates in Appendix 1. Perhaps the most interesting result of the landbird survey was that no Collared kingfishers (Halcyon chloris, sihek) were found on Guguan. The most numerous birds were Micronesian starlings (Aplonis opaca, sali) followed by Micronesian honeyeaters (Myzomela rubratra, egigi). The endangered Micronesian megapode (Megapodius laperouse, sasangat) was plentiful, while White-throated ground-doves (Gallicolumba xanthonura, paluman apaka) and Intermediate egrets (Egretta intermedia) were rare (Table 1). Anecdotally, 15 White-throated ground-doves were observed foraging on the ground in an AglaialTerrninalia forest on 6 June. Most of the doves were males, but several females were also present. Similar sized groups have also been observed previously on Saipan, Aguiguan, and Rota (Villagomez, 1987). Transect 4, Guguan June 2000 Table 1 . Detections of land birds on Guguan, 6-7 June 2000. Detections Approximate Bird Species Number per Station numbers expected Detected (SE) in a 40 ha area Micronesian honeyeater 79 2.17 (0.266) 49.8 Micronesian megapode 34 0.94 (0.214) 21.5 Micronesian starlinQ 137 3.81 (0.481) 86.5 White-throated Qround-dove 5 0.14 (0.081) 3.2 Intermediate egret 1 0.03 0.6 TOTAL 256 7.11 164.1 The large disparity between habitat types on Guguan could easily be an influence on the distribution of land birds on the island. Therefore, point count stations were classified into two vegetation types: (1) open habitats including lava flows, cinder fields, open grassy areas, and savanna; and (2) forested habitats including mixed successional forest and more mature native forest. With this break down Micronesian megapodes and White-throated ground-doves were most frequently found in forested as opposed to open habitats.